Geotechnical Aspects of N(H)bSs for Enhancing Sub-Alpine Mountain Climate Resilience

Abstract

Mountain resilience is the ability of mountain regions to endure, adapt to, and recover from environmental, climatic, and anthropogenic stressors. Due to their steep topography, extreme weather conditions, and unique biodiversity, these areas are particularly vulnerable to climate change, natural hazards, and human activities. This paper examines how nature-based solutions (NbSs) can strengthen slope stability and geotechnical resilience, with a specific focus on Slovenia’s sub-Alpine regions as a case study representative of the Alps and similar mountain landscapes worldwide. The proposed Climate-Adaptive Resilience Evaluation (CARE) concept integrates geomechanical analysis with geotechnical planning, addressing the impacts of climate change through a systematic causal chain that connects climate hazards, their effects, and resulting consequences. Key factors such as water infiltration, soil permeability, and groundwater dynamics are identified as critical elements in designing timely and effective NbSs. In scenarios where natural solutions alone may be insufficient, hybrid solutions (HbSs) that combine nature-based and conventional engineering methods are highlighted as essential for managing unstable slopes and restoring collapsed geostructures. The paper provides practical examples, including slope stability analyses and reforestation initiatives, to illustrate how to use the CARE concept and how NbSs can mitigate geotechnical risks and promote sustainability. By aligning these approaches with regulatory frameworks and climate adaptation objectives, it underscores the potential for integrating NbSs and HbSs into comprehensive, long-term geotechnical strategies for enhancing mountain resilience.

1. Introduction

Land refers to the Earth’s surface and its diverse natural resources, including soil, minerals, water, rock, and vegetation. It is examined through various disciplines, which can be categorized according to physical, legal, economic, environmental, cultural, and geopolitical dimensions. Each of these perspectives provides valuable insights, positioning land as a critical subject in multiple applied fields.

Land management involves the sustainable use and administration of land resources to meet both present and future human needs while preserving ecological balance. This process includes the planning, development, conservation, and maintenance of land for purposes such as urban development, agriculture, forestry, and nature conservation. Effective land management addresses key issues like soil health, water resources, biodiversity, climate change, and land degradation, striving to balance environmental, social, and economic factors to promote long-term sustainability [1,2,3].

Land resilience is the ability of land and ecosystems to endure, recover, and adapt to disruptions and is crucial for managing natural and human-induced pressures [4]. This paper evaluates resilience from a geotechnical perspective, considering factors like topography, climate, and biodiversity. Mountain regions face heightened risks due to steep slopes, erosion, and extreme weather, requiring tailored strategies. The Climate-Adaptive Resilience Evaluation (CARE) concept assesses threats, impacts, and risk-reduction measures, emphasizing geotechnical challenges and climate-adaptive design. A case study of a Slovenian landslide illustrates practical applications. The paper concludes with recommendations for integrating climate considerations into geotechnical planning for mountain resilience.

Vulnerabilities associated with climate change in mountain regions are significant. Rubel et al. [5] present Köppen–Geiger climate classification maps for the Alpine region, detailing temperature and precipitation patterns from 1976 to 2000 and projected changes for 2076–2100 under different scenarios. Rising temperatures enhance glacier melt, disrupt hydrological cycles, and affect water availability downstream. Furthermore, shifting precipitation patterns can lead to increased flooding and prolonged droughts, necessitating adaptation by both ecological and social systems [6].

To strengthen the resilience of mountains, nature-based solutions (NbSs) are crucial [7]. These solutions use natural processes that can be used to sustainably address societal challenges, including reforestation, soil stabilization, and restoration of natural water systems [8,9,10]. NbSs can help manage environmental risks while enhancing biodiversity and ecosystem services [11].

Numerous studies have investigated the resilience of mountain communities in response to various drivers of change, including climate impacts, environmental degradation, and modernization [12,13,14,15,16]. Wyss et al. [17] and Burgos [18] provide a comprehensive overview, emphasizing livelihoods, disaster prevention, and climate change.

The proposed concept for climate-adaptive resilience evaluation aims to identify adaptation strategies for geostructures in the context of climate change by integrating the complexities of climate hazards and their implications into geomechanical analysis. Although this specific concept is not the focus of the current paper, it can be illustrated through typical slope stability analyses in Slovenia’s sub-Alpine region, highlighting critical factors that influence slope stability [19,20].

Current engineering practices in geotechnical design often overlook climatic influences, resulting in several significant challenges. First, there is a lack of climate considerations in existing regulations, leaving a gap in addressing emerging environmental conditions. Second, applying tailored geomechanical approaches for different structures proves difficult, as each structure requires specific adaptations to account for varying conditions. Third, translating climate projections into actionable geomechanical data remains a challenge due to the complexity and variability of climate models. Fourth, uncertainties surrounding the effects of climate change on ground mechanical properties hinder precise planning and decision-making. Finally, conventional methodologies often fail to adequately address the multifaceted nature of these challenges, underscoring the need for innovative approaches to integrate climate considerations into geotechnical design.

2. Land Resilience Evaluation

Land is a finite resource, and its allocation must be strategic and thoughtful to ensure that it can withstand the growing pressure of increasing demand for housing, industry, and infrastructure. Land use planning and land management are therefore essential to maintain the resilience of land in the face of population growth, urbanization, and infrastructure expansion [21].

Urban sprawl and the expansion of the built environment place significant pressure on agricultural land, natural habitats, and water resources. Without proper planning and management, land can degrade, leading to soil erosion, flooding, loss of biodiversity, and uncontrolled urban growth. Effective spatial planning must incorporate solutions that maintain the natural functionality of the land, including geotechnical measures to mitigate flooding, landslides, and soil degradation, as well as ecosystem protection strategies that support climate adaptation and resilience to extreme weather events.

Urbanization requires development that minimizes urban sprawl and optimizes land use while preserving green spaces. These green spaces serve as natural water retention zones, reduce the urban heat island effect, and increase the well-being of residents. Well-planned and -managed land must accommodate increasing population densities, transportation infrastructure, and utilities without compromising sustainability or ecological balance.

Key components of land resilience include ecosystem functions, such as nutrient cycling and photosynthesis, which are vital for maintaining ecosystem health and stability; structural stability, which involves preserving soil fertility and habitat integrity to support diverse life forms; and adaptability and mitigation, which refer to the land’s ability to respond to environmental changes and mitigate impacts like soil erosion and biodiversity loss.

Indicators of land resilience encompass soil quality, biodiversity levels, recovery capacity after disturbances, and long-term productivity. However, evaluating land resilience requires a geotechnical perspective that incorporates factors such as topography, geological properties, hydrology, and climate. This complexity is further influenced by variables like population density, land use, and climate, which necessitate classifications into categories such as urban, suburban, rural, industrial, and transportation areas.

Given the diverse nature of threats and interactions in geotechnical contexts, a variety of analytical approaches is necessary to address the resilience needs of different landscapes and structures effectively.

Threats to land resilience stem from diverse sources, including climate-related challenges, pollution, unsustainable land use, biodiversity loss, water management issues, and economic pressures, each with severe consequences. These threats degrade soil, disrupt ecosystems, reduce biodiversity, and compromise critical services like water filtration, carbon storage, and food production. Industrial activities, climate impacts, and resource competition exacerbate these issues, leading to agricultural decline, population displacement, and socio-economic instability. The cascading effects of ecosystem collapse, habitat fragmentation, and arable land loss further amplify food insecurity and environmental crises. Addressing these interconnected challenges requires integrated strategies that combine environmental, economic, and social dimensions to safeguard land resilience, restore ecosystems, and ensure sustainable management for long-term socio-economic and environmental stability [22,23].

3. Resilience of Mountain Environments

Building on the evaluation of land resilience, it is essential to examine the specific concept of mountain resilience, which presents unique challenges. The term “mountain resilience” has evolved within resilience studies and gained prominence in mountain research since the 1980s, alongside efforts in sustainable development and disaster risk reduction in these regions [17]. A comprehensive framework for mountain resilience requires an integrated approach that considers community stability, ecosystem protection, and disaster preparedness. Mountains are characterized not only by their elevation and steep slopes but also by the complex interactions of ecological, climatic, and human factors. Understanding mountain resilience necessitates examining these dynamic relationships, where geological features significantly influence biodiversity and human activities. Distinguishing between “mountain areas” (defined by terrain) and “mountain environments” (which encompass the interactions within these systems) is crucial for effective resilience strategies. Due to their challenging ecological conditions, mountain areas require adaptation, innovation, and the maintenance of fundamental capacities that enable mountain communities to cope with multiple stresses, such as droughts, floods, and earthquakes [24,25].

Key features of mountains vary depending on the specifics of individual regions or countries. For instance, in Slovenia, mountains are defined by criteria including elevation, steepness, formation, and climate [26,27]. Typically, mountains rise to at least 600 m above the surrounding landscape and are characterized by steep slopes and either sharp or rounded peaks. Most mountains arise from tectonic plate movements (such as folding and faulting), volcanic activity, or the erosion of adjacent land. Higher elevations often experience colder temperatures, which create distinct vegetation and climate zones, including snow-capped peaks. In contrast, hills are natural landforms that rise above the surrounding terrain but are smaller and less steep than mountains. While there is no universally accepted height that differentiates a hill from a mountain, hills typically have heights below 600 m and more gradual slopes.

Section 2 provides a thorough overview of the threats, their impacts, and the consequences for land resilience, which are equally important for mountain resilience. Climate-related threats, including extreme weather events, rising temperatures, and changing precipitation patterns, contribute to glacier retreat, altered water availability, and more frequent and intense weather phenomena. These changes result in infrastructure damage, reduced water resources, and challenges to agriculture and hydropower systems. Environmental threats such as soil erosion, landslides, and deforestation degrade the land, disrupt ecosystems, and reduce biodiversity, leading to lower agricultural productivity, habitat loss, and a decline in critical ecosystem services. Human activities like overgrazing, unsustainable tourism, and resource extraction worsen these problems by intensifying soil degradation, pollution, and habitat disturbance, causing long-term environmental harm. These interconnected challenges underscore the urgent need for integrated strategies to enhance mountain resilience. This requires a focus on sustainable practices and active community participation to ensure the stability of these vital ecosystems. Mountain resilience refers to the capacity of these regions to absorb, adapt to, and recover from both natural and human-induced disturbances. Strengthening resilience demands a comprehensive approach that integrates conservation, sustainable land management, climate adaptation, and infrastructure development. The resilience of mountain ecosystems relies on the complex interaction of environmental, social, economic, and climatic factors, highlighting the need for strategies that maintain their ecological balance and cultural heritage [28].

A detailed assessment of threats, their impacts, and the resulting consequences for land resilience is applied to Slovenia, a country characterized by its diverse geography and ecosystems. Situated in the sub-Alpine region, Slovenia spans three distinct climatic zones—Alpine, Continental, and Mediterranean—which contribute to its varied landscapes and rich biodiversity. Agricultural land covers approximately 33% of the country, equivalent to about 673,000 hectares, while urban areas occupy 7% of the territory [29]. Notably, 37% of Slovenia’s land is part of the EU’s Natura 2000 network [30], a biodiversity protection initiative. This percentage is more than double the EU average of 18% and directly impacts around 7% of Slovenia’s population. Slovenia’s predominantly mountainous and hilly terrain further distinguishes its geography, with mountains covering nearly half the country and hilly regions contributing to almost two-thirds of the total area. Forests, which are integral to Slovenia’s ecological and economic health, blanket approximately 55% of the nation, underscoring its commitment to preserving natural resources and sustaining ecological balance.

3.1. Geotechnical Aspects of Mountain Resilience

Climate change resilience emphasizes the susceptibility of mountainous areas to rising temperatures, altered precipitation patterns, and glacial melt. In this context, resilience is defined by the capacity of ecosystems to adapt to these changes while continuing to provide essential services, including water supply, carbon storage, and wildlife habitats. In recent years, the resilience of mountain communities to various factors of change has been studied, with a particular focus on climate change. Average warming rates at higher elevations are above the global average [31], while shifts in precipitation patterns further exacerbate risks to livelihoods and ecosystems in mountain regions [32].

Biodiversity resilience highlights the ability of mountain ecosystems to support a diverse array of endemic species, ensuring genetic variability and adaptability in the face of threats such as habitat loss and climate variability. In addition to climatic factors, globalization [33] and the mismanagement of biodiversity [34] also play an important role in shaping living conditions in mountain regions. Concurrently, socio-economic resilience addresses the challenges faced by mountain communities, which often depend on limited resources and vulnerable industries. This dimension encompasses the capacity of these communities to recover from economic shocks and natural disasters while preserving their cultural heritage and fostering social cohesion.

Mountainous regions are particularly susceptible to natural hazards like landslides and earthquakes, which can disrupt ecosystems and displace communities, resulting in significant losses of life and livelihood. Mitigating these impacts requires a multifaceted approach that integrates sustainable land management, conservation initiatives, and climate adaptation strategies. Engaging local communities and implementing policies across local, national, and international levels are essential for upholding ecological integrity, cultural heritage, and socio-economic stability within mountainous environments.

A thorough understanding of the causal chain linking threats, effects, and consequences is critical for the effective management of mountain resilience. To facilitate this understanding, a conceptual framework is proposed, integrating characteristics specific to mountain resilience with identified threats, their effects, and the resultant consequences. This framework builds upon the general causal-chain model for land resilience while being tailored to the unique conditions presented by mountainous environments.

The framework is designed to promote flexibility, allowing for distinct approaches based on geotechnical, ecological, or social perspectives, while emphasizing the importance of examining the interactions between these aspects in relation to the area’s fundamental characteristics. The diversity of threats to mountain resilience leads to varying effects and consequences depending on the analytical lens used. From a geotechnical standpoint, the complexity of these issues is significant, and relying on a single method is insufficient. A comprehensive analysis must address the multiple threats, effects, and consequences tied to different geostructures, underscoring the need for multidisciplinary approaches to fully understand and manage the factors that influence mountain resilience.

Table 1. Geotechnical threats, effects, and consequences for mountain resilience.

Threats	Effects	Consequences
Climate Change	Modifies groundwater, soil, and rock characteristics; enhances weathering processes.	Increased erosion, slope instability, permafrost degradation, altered groundwater, higher sediment loads.
Land Use Changes	Soil compaction, habitat loss, altered runoff and sediment transport.	Slope destabilization, landslides, drainage disruptions, long-term erosion.
Natural Resource Over-Exploitation	Weakening of rock masses and soil stability.	Landslides, subsidence, soil degradation, and slope destabilization.
Pollution	Degradation of soil and rock quality from agricultural runoff, industrial waste, and chemical leaching.	Contaminated aquifers, increased erosion, and weakening of geotechnical structures.
Waste	Soil contamination, reduced shear strength, altered permeability.	Risk of slope failure, groundwater contamination, and long-term impacts on soil stability and ecosystem health.
Invasive Species	Disrupts soil cohesion and hydrology through non-native plant roots.	Increased erosion, slope destabilization, landslides and soil degradation.
Infrastructure and Traffic	Habitat fragmentation, pollution, stress changes in subsurface layers.	Landslides, subsidence, disruption of natural processes.
Energy Development	Slope modifications from hydropower dams, wind farms, and mining impacts.	Seismicity, slope failures, hydrological disruption, soil and rock deformation.
Ecosystem Shifts	Changes in vegetation patterns and species distributions.	Increased soil erosion, reduced slope stability, and cascading effects on sedimentation and ecosystem health.
Loss of Ecosystem Services	Decline in stabilizing vegetation and critical soil processes.	Soil degradation, slope instability, vulnerability to natural disruption.
Economic Impacts	Environmental degradation and biodiversity loss harm tourism, agriculture, and forestry.	Reduced income for local communities, increased geotechnical management costs, and economic instability.

highlights key threats to mountain resilience, focusing on geotechnical impacts, effects, and consequences. Threats like climate change, land use changes, pollution, and resource depletion disrupt geotechnical stability through soil compaction, erosion, and altered hydrology. These lead to slope instability, soil degradation, and resource contamination, increasing risks of landslides, permafrost thawing, and weakened structural integrity. The cascading environmental and socio-economic impacts, including habitat loss, reduced ecosystem services, and heightened disaster vulnerability, underscore the need for sustainable geotechnical strategies to protect mountain stability.

3.2. Engineering Geostructures for Resilient Mountain Environments

Geostructures are engineered structures designed to interact with and adapt to the characteristics of the ground. Their design and performance are significantly influenced by a range of environmental factors, such as climate, geological features, and hydrological dynamics. In mountainous regions, effective geostructures play a key role in increasing resilience by stabilizing slopes, managing water flow, and protecting ecosystems [35]. The relationship between typical geostructures and their effects on mountain resilience is summarized in

Table 2. Typical geostructures and their impact on mountain resilience.

Type of Geostructures	Ecosystem and Climate Impacts
Natural/Engineered Slopes	Provide habitats and regulate water flow. They can disrupt ecosystems and drainage, while vegetation helps with stabilization.
Embankments	Alter hydrology, create wildlife barriers, and impact water flow.
Foundations	Compact soil, increase runoff, and reduce groundwater recharge.
Retaining Walls	Stabilize slopes but may disrupt water flow and habitats, increasing erosion if poorly managed.
Bridge Abutments	Modify river flow, sediment transport, and aquatic habitats.
Pipelines	Impact groundwater flow and soil moisture; pose pollution risks from leaks.
Dikes and Levees	Control flooding but alter ecosystems and floodplain dynamics, increasing downstream risks if not maintained.
Slope Stabilization Structures	Enhance stability but disrupt local ecosystems through land alterations.
Green Infrastructure	Boost resilience, improve water quality, provide habitats, mitigate urban heat, and reduce carbon emissions.

. We also include natural slopes as geostructures here. This overview shows how different geostructures can mitigate environmental impacts, increase stability, and promote sustainable practices in rugged terrain [17].

3.3. Geotechnical Factors Influencing Slope Stability and Landslide Classification

Effective slope stability management is crucial for ensuring the safety and durability of civil engineering projects, infrastructure, and natural landscapes. In geotechnics, a “slope” refers to an inclined surface composed of soil, rock, or other materials. Slope stability is a critical aspect of geotechnical engineering, which involves assessing the safety and integrity of slopes to prevent landslides, erosion, and other forms of failure.

This paper explores the key geotechnical factors influencing slope stability, including soil properties and conditions that affect the performance of slopes in mountainous regions. A thorough understanding of soil and rock physical properties, along with water flow dynamics, is essential for evaluating slope stability and developing effective intervention strategies [36]. Key factors include soil permeability, groundwater levels, and surface water infiltration, all of which significantly influence the stability of slopes and geostructures.

To address the challenges posed by potentially unstable geostructures, we propose a structured approach for identifying adaptation measures. This methodology incorporates rigorous geomechanical analysis that anticipates the impacts of climate change on slope stability and integrates these considerations into geotechnical planning.

Landslides are a major concern for slopes, and their classification is important for hazard assessment. The basic landslide velocity classification, established by Varnes [37] and expanded by Cruden and Varnes [38], provides a framework for understanding landslide behavior. The International Union of Geological Sciences (IUGS) Working Group on Landslides and subsequent contributions by Hungr et al. [39] have refined this system and provided a comprehensive understanding of landslide behavior. Highland et al. [40] have also compiled a practical guide to landslide types and rates of movement, which is widely used in educational and hazard-reduction contexts. Based on the above,

Table 3. Landslide classifications.

Classification	Types
Material Type	Rock: Bedrock or large fragments Soil: Fine-grained materials (clay, silt, sand, gravel) Debris: Mix of rock, soil, and organic matter
Movement Type	Falls: Sudden free fall of material (e.g., rockfall, debris fall) Topples: Forward rotation (e.g., rock topple, soil topple) Slides: Movement along a failure plane (rotational or translational) Flows: Viscous movement (e.g., debris flow, mudflow, earthflow, lahar) Creep: Slow, imperceptible movement Spreads: Lateral extension (e.g., lateral spreads, liquefaction)
Rate of Movement	Extremely Rapid: >5 m/s (e.g., rockfalls) Very Rapid: 0.05–5 m/s (e.g., debris flows) Rapid: 0.0005–0.05 m/s (e.g., fast earthflows) Moderate: 0.00002–0.0005 m/s (e.g., slow slides) Slow: 0.0000007–0.00002 m/s (e.g., creep) Very Slow: 0.00000005–0.0000007 m/s (e.g., deep-seated creep) Extremely Slow: <0.00000005 m/s (e.g., tectonic movement)
Depth	Superficial, affecting top layers Shallow: ≤2 m medium deep: 2–5 m Deep: 5–12 m Very deep: ≥12 m

presents landslides classified by material type, type of movement, velocity, and depth, as reported in the geotechnical literature and hazard guidelines.

4. Climate Vulnerability and Slope Stability in Mountain Regions

Mountain regions, characterized by steep topography, extreme weather conditions, and unique biodiversity, are particularly vulnerable to the adverse effects of climate change, natural disasters, and anthropogenic activities. This vulnerability stems from their sensitivity to environmental stressors, which can exacerbate impacts on both ecosystems and human settlements.

Several factors influence slope stability in mountainous regions, interacting with geological, climatic, and geomechanical properties to affect the behavior of slopes.

Slopes can be natural or engineered. Natural slopes are shaped by erosion, sediment deposition, and tectonic forces, while engineered slopes are created through excavation and construction activities. The geometry and curvature of a slope also play a crucial role in how stresses and water are distributed, impacting its vulnerability to erosion or collapse.

Geological factors, such as rock type, structure, faults, fractures, and soil composition, are fundamental to slope stability. Soft, weathered rocks are more prone to erosion, and fractures create weak zones that can lead to slope failures. Soil types, especially clay-rich soils, can become saturated and trigger instability.

Climatic conditions directly affect slope stability. High rainfall can saturate the soil, increasing the risk of landslides, mudslides, or rockfalls.

The material properties of a slope, including cohesion, friction angle, and density, determine its resistance to sliding. Water content is also significant, as it weakens soil cohesion and increases pore pressure. Fluctuating groundwater levels and erosion due to runoff can further destabilize slopes, particularly during heavy rain or snowmelt.

External loads, such as the weight of buildings, roads, or vehicle traffic, can impose additional stress on slopes, potentially leading to failure if not properly accounted for in design.

Vegetation helps stabilize slopes by binding the soil with roots, preventing erosion. However, removing vegetation through deforestation or wildfires can lead to increased erosion and instability.

Seismic activity, including earthquakes and tectonic movements, can destabilize slopes by shaking loose soil or rock, potentially triggering failures. Tectonic forces also cause long-term deformations in the landscape, creating fault zones and fractures that further weaken slope integrity.

4.1. Overview of Climate Threats

The European Large Geotechnical Institutes Platform [41] is a network of leading European geotechnical research institutes committed to advancing geotechnical science and tackling critical challenges such as sustainable land use and climate change adaptation. The Sustainability Working Group [42] promotes development that meets present needs without compromising future generations. In geotechnical engineering, this includes reusing waste materials and foundations, using eco-friendly materials, and minimizing the environmental and climate impact of geotechnical solutions. The Climate Change Adaptation Working Group [43] within the ELGIP focuses on addressing climate-related risks. It has developed an innovative causal-chain framework that connects climate change signals to their effects, structural responses, and potential mitigation strategies. This framework provides a systematic approach to identifying climate signals, assessing their impacts, analyzing correlations, and formulating effective solutions to these challenges.

Climate threats to mountain resilience are often described through measured climate parameters, which provide a broad overview of changes occurring in the climate system. Common climate change threats include altered precipitation patterns, reduced rainfall, extended dry periods, higher air temperatures, warmer winters, increased cycles of heavy rain and drought, more frequent freeze–thaw cycles, intensified storms, and stronger winds. However, these parameters are typically too generalized to directly address specific geotechnical challenges.

Climate parameters are derived from empirical data and projections based on selected climate scenarios, reflecting both current and anticipated trends [44]. These parameters are essential for the analysis, planning, and design of geostructures in mountainous regions. Climate scenarios are typically framed using Representative Concentration Pathways (RCPs), which outline potential greenhouse gas concentration trajectories. The four primary RCPs represent different emission scenarios: the low-emission mitigation scenario RCP2.6, the intermediate scenarios RCP4.5 and RCP6.0, and the high-emission scenario RCP8.5. Incorporating these scenarios into geotechnical analyses ensures that both present and future climate trends are considered, leading to more resilient designs and adaptive measures for mountain regions.

4.2. Effects of Climate Threats

Climate threats have diverse impacts on soils, bedrock, groundwater, surface waters, and vegetation, which subsequently influence the behavior and properties of soils and structures. These impacts, attributed to climate change, are analyzed by geological and geotechnical experts using climatological data.

Climate change impacts slope stability through a range of processes. One major effect is the decreased strength of soil and rock, where disruptions in the balance between shear strength and gravity lead to an increased risk of landslides or rockfalls. Increased weathering due to higher temperatures and drier conditions accelerates the breakdown of soils, weakening their cohesion and overall stability.

Furthermore, increased rainfall and water erosion result from more frequent and intense storms, which accelerate soil erosion and degradation. This, in turn, heightens the likelihood of slope failure. Along with this, increased surface runoff during heavy rain events exacerbates flooding and erosion of slopes, as the water cannot be absorbed quickly enough.

Changes in water dynamics are also noticeable in groundwater levels. Increased rainfall or snowmelt raises groundwater levels, affecting soil moisture and contributing to slope instability. On the other hand, prolonged droughts can lower groundwater levels, reducing moisture and further weakening the stability of slopes.

Additionally, increased wind erosion is a result of vegetation loss, often due to drought or land use changes, which exposes the soil to wind erosion. Freeze–thaw cycles also play a role in altering the properties of frozen soils, leading to instability as the freezing and thawing process weakens the soil’s structure. Lastly, increased runoff from snowmelt is caused by warmer temperatures, which speed up the melting of snow, contributing to both erosion and potential flooding in mountainous regions.

The described climate threats and effects are relevant to slope stability and resilience. Climate threats are indicators of broader climate trends, such as precipitation patterns, temperature shifts, and increased storm activity, while their effects describe the direct impacts of climate-related changes on slopes. Both sets of information are essential for understanding how climate change is influencing the geotechnical properties and stability of slopes.

4.3. Consequences of Climate Threats

Typical consequences of climate signals and their effects on mountain resilience are summarized in

Table 4. Consequences of climate threats and associated effects on land.

Consequences	Description
Slope Instability, Landslides	Climate change, deforestation, and road construction reduce soil cohesion, increasing landslides and rockfalls.
Soil Erosion	Improper waste disposal, deforestation, and overgrazing accelerate erosion, weakening slopes and vegetation support.
Riverbank Erosion and Flooding	Increased glacial melt and rainfall lead to riverbank erosion and flooding, threatening infrastructure and ecosystems.
Soil Weakening	Erosion, thawing of permafrost, or loss of vegetation reduces soil cohesion, making it prone to sliding or collapsing.
Debris Flows	Heavy rainfall and glacial melt create debris flows of mud, rock, and organic material, damaging infrastructure.
Permafrost Thaw	Thawing of permafrost weakens soil through loss of ice content, leading to ground subsidence and increased instability.
Rock Fracturing	Temperature fluctuations or glacial retreat alter pressure on rock, causing fractures and weakening rock mass, increasing landslides and rockfalls.
Snowpack Destabilization	Temperature rise or human activity destabilizes snowpacks, increasing avalanche risk.
Hydraulic Pressure Changes	Increased rainfall or snowmelt adds weight and water pressure, reducing friction in soil/rock layers, triggering slippage.
Avalanches	Warming temperatures and human activity destabilize snowpacks, triggering destructive avalanches.
Infrastructure Damage	Erosion, landslides, and permafrost thaw weaken foundations of buildings and roads, leading to safety risks and increased costs.

. Based on these identified consequences, the appropriate response must be determined in accordance with the European standards Eurocode 7 and 8 [45,46]. This response is typically expressed either as an increase in applied loads or as changes (often deterioration) in the material properties of geostructures. The response of structures to climate change and its consequences depends on a variety of factors. Given the significant variability among geostructures, there are multiple approaches to their design and construction. Even when focusing specifically on slopes, it is clear that the manifestations of instability are diverse, shaped by factors such as the geometry and stratigraphy of a slope, the properties of the unstable mass, and the influence of climate signals and their effects. The ELGIP WG CCA conducted a study using a survey primarily distributed to geotechnical societies within ELGIP member states. The study qualitatively assessed the significance of climate change signals and their impact on geostructures across various European countries [35]. The survey results indicated that, in most countries, the most critical climate change signals were increased precipitation and flooding.

This paper explores the geotechnical aspects of slope stability, soil properties, and overall geotechnical conditions, proposing a comprehensive approach to mitigating and adapting slopes through solutions primarily based on natural processes.

4.4. Measures for Slope Stability

A variety of strategies exist for preventing slope instability and remediating landslides. These strategies include nature-based solutions, hybrid methods, and conventional engineering approaches. Each option presents unique benefits and drawbacks, with the selection often influenced by factors such as the specific characteristics of the site, the level of landslide risk, and the intended ecological and social objectives. By integrating these diverse strategies, it becomes possible to develop more effective and sustainable solutions for managing landslide risks.

5. Climate-Adaptive Resilience Evaluation Concept

Approaches to addressing climate change are typically categorized into strategies aimed at achieving climate neutrality and those focused on mitigating the impacts of climate change. The approach presented here involves a comprehensive geomechanical analysis designed to anticipate the effects of climate change on slope stability and inform geotechnical planning. This analysis should encompass the entire causal chain of climate hazards, their subsequent effects, and the resulting consequences. Such an approach ensures that all potential risks are systematically identified and thoroughly addressed during the planning process. The CARE concept for slopes is presented in Figure 1.

This concept adopts a structured model that delineates the causal chain linking climate hazards, their effects, and the resulting consequences. It provides a systematic framework for analyzing slope stability challenges and making informed decisions. The causal chain is presented as a logical sequence: climate threats trigger specific effects, which in turn lead to measurable consequences. Grasping this interconnected process is crucial for effective risk management and the development of targeted interventions.

Key Steps in the Process:

• Input Data—Characterization: Collecting detailed information on slope properties and geotechnical conditions, including material composition, slope geometry, and vegetation cover.
• Climate Threats: Identifying climate-related hazards, such as increased rainfall intensity, temperature fluctuations, and shifting weather patterns.
• Climate Effects: Evaluating the direct impacts of these threats, including changes in soil moisture levels, erosion rates, and slope stability.
• Consequences: Analyzing the broader implications, such as habitat degradation, infrastructure damage, and heightened landslide risks.

The measures are an important intermediate step for the development and implementation of measures to mitigate the identified risks, with a focus on preventing instability and erosion.

At the core of this approach is the principle of causality. Identifying the root causes of observed consequences involves iterative analysis, where these causes are continuously refined and re-evaluated as input data in an analytical framework. This methodology enables a deeper understanding of the interdependencies between climate threats, their effects, and the resulting consequences, paving the way for proactive and effective risk management solutions.

By mapping these relationships, stakeholders can identify effective measures to mitigate risks and enhance slope stability in the face of a changing climate. Furthermore, this framework supports proactive decision-making, allowing for the integration of adaptive strategies that consider future climatic scenarios, thus ensuring long-term resilience in mountain regions.

5.1. Approaches for Achieving Climate Neutrality

Achieving climate neutrality involves implementing regulatory and management strategies that incorporate nature-based solutions (NbSs). These solutions are inspired by natural processes and supported by ecosystems, providing cost-effective measures that yield environmental, social, and economic benefits. By introducing greater biodiversity and natural elements into urban, rural, and marine areas, NbSs facilitate effective, locally adapted, and systemic interventions [7].

Key approaches for climate neutrality include greening initiatives, afforestation, soil restoration, the utilization of natural sediments, and low-impact environmental solutions. These measures can influence climate conditions and indirectly affect soil health and infrastructure by regulating temperature, managing extreme rainfall, and improving water infiltration. While individual actions may have limited short-term results, their cumulative impact can be significant. Therefore, a coordinated and systemic strategy, bolstered by robust regulatory frameworks, is critical for effective climate change mitigation.

This paper emphasizes the role of NbSs as cost-effective strategies for enhancing mountain resilience, providing numerous ancillary benefits. The analysis views mountain resilience through a geotechnical lens, evaluating typical geostructures via established methodologies. It introduces the concept of climate-adaptive geotechnical analysis and planning as an essential method for preserving or improving the resilience of both existing and new structures in mountainous regions. Nature-based solutions offer sustainable approaches to address environmental challenges while reinforcing mountain resilience. By harnessing natural processes and ecosystems, NbSs help mitigate climate-related risks, adapt to changing conditions, and restore degraded environments. When NbSs alone cannot fulfill all geotechnical requirements, combining them with hybrid solutions (NHbSs) presents significant advantages. These hybrid methods integrate natural techniques with traditional engineering practices to effectively manage complex geotechnical issues. The paper outlines the planning steps, criteria, and measures necessary for new and existing structures, elucidating the distinctions between conventional solutions, NbSs, and hybrid solutions (NHbSs).

5.2. Approaches to Climate Change Mitigation

Mitigating the impacts of climate change requires multifaceted geotechnical and engineering strategies that aim to enhance environmental resilience and reduce vulnerability to climate-induced stresses. Effective slope stabilization techniques, such as retaining walls, soil nailing, and vegetation reinforcement, are essential for preventing landslides and mitigating erosion exacerbated by extreme rainfall and temperature fluctuations. These techniques, particularly vegetation reinforcement, may be more sustainable compared to traditional methods. Vegetation helps restore natural ecosystems, improves water retention, and reduces soil erosion over the long term, making it an environmentally friendly and cost-effective solution for slope stabilization.

Ground improvement measures, such as compaction, soil grouting, and the use of geosynthetics, enhance soil strength and stability, enabling soils to better withstand climate-related stressors. Erosion control strategies, including riprap, terracing, and bioengineering, are implemented to combat soil degradation in areas increasingly affected by intensified precipitation or rising sea levels.

Advanced drainage systems are critical for managing excess water from heavy rainfall, thereby reducing the risk of slope failure and subsurface erosion. Flood and coastal defense structures, such as levees, seawalls, and dikes, provide vital protection against flooding and erosion caused by sea-level rise and storm surges. In colder regions, thermal stability solutions, including thermal insulation and active cooling methods, help counteract permafrost thaw and preserve ground stability.

Monitoring and early warning systems, utilizing geotechnical instruments such as inclinometers and piezometers, continuously assess slope movement, groundwater levels, and soil conditions, allowing for timely and proactive interventions.

Sustainable material use prioritizes low-carbon materials, recycled aggregates, and locally sourced resources, minimizing the environmental footprint of geotechnical projects. Nature-based engineering solutions integrate ecological processes, such as vegetation, bioengineering techniques, and natural buffers, to enhance slope stability, reduce surface runoff, and promote ecological balance, effectively mitigating the direct impacts of climate change and fostering long-term sustainability.

5.3. Planning Steps, Criteria, and Measures for Slopes

Effective planning for new structures requires conducting a comprehensive climate change analysis, followed by the development of an appropriate design. For existing slopes, the response strategy depends on the anticipated consequences of climate change. If soil degradation and reduced stability are observed, renovations will follow the same methodology as for new structures.

Climate change analysis is crucial to prevent worst-case scenarios, such as structural damage or failure, exemplified by triggered landslides. In these cases, emergency measures must be implemented promptly.

Table 5. Planning steps, criteria, and measures for new and existing geostructures.

Planning Steps: Safety and Usability Criteria, Considering Climate Change	New Geostructure: New Planning	Existing Geostructure: No Damage Found—Check Safety and Usability of Geostructure	Existing Geostructure: Damage Found—Take Emergency Measures and Redesign
Feasibility Study	✔	✔	✔
Initial Design	✔	-	✔
Detailed Design	✔	-	✔
Evaluation	✔	✔	✔
Implementation	✔	-	✔

logically organizes project steps, distinguishing between new and existing geostructures—whether damage has been identified or not. Each row corresponds to specific planning steps, aligned with international standards [45], and outlines the appropriate actions for each type of geostructure.

Feasibility Study and Emergency Measures: This step applies to both new and existing geostructures. It assesses the feasibility of the design and ensures the implementation of emergency measures if necessary.

Initial Design: Primarily focused on new geostructures, this step may also be relevant for existing structures undergoing modification or expansion.

Detailed Design: Similar to the initial design stage, this step applies to new geostructures and to existing ones if significant damage is identified.

Evaluation: This involves assessing the performance of the geostructure for both new and existing structures, ensuring compliance with safety and usability criteria.

Implementation: The execution of the design and associated plans, applicable to both new structures and repairs for existing ones.

Safety and Usability Criteria Considering Climate Change: New designs incorporate climate change considerations. For existing structures, checks and emergency measures are activated when damage is identified or when redesign is necessary.

Redesign (if necessary): If significant damage is found in existing geostructures, redesign or remedial measures will be undertaken.

5.4. The Role of the Interface in Geomechanical Analyses

Defining the interface between geological, climatic, and geomechanical data is a critical component of slope stability analysis. Key factors influencing stability include precipitation, water runoff, evaporation, net water infiltration, permeability, cohesion, and friction angle. These interrelated parameters play a central role in assessing and understanding slope stability.

Net water infiltration exemplifies how data are converted into usable parameters. For instance, water infiltration during rainfall depends on surface soil properties, vegetation cover, weather conditions, and drainage systems. This infiltration influences soil permeability, which changes over time, and increases soil moisture and water saturation. These changes reduce the internal friction angle and cohesion, thus lowering soil shear strength.

Water infiltration and evaporation at the soil surface are primarily influenced by climatic conditions and soil water content [47]. Precipitation that reaches the slope surface is partially intercepted by vegetation, where evaporation occurs—a process known as interception. After interception losses, the remaining water reaches the soil surface. If precipitation exceeds the soil’s infiltration capacity, the excess results in surface runoff. Factors like slope angle, vegetation cover, and surface roughness significantly affect runoff, while soil hydraulic conductivity primarily governs the infiltration process, which varies with changing soil suction levels.

The water infiltrating the soil affects pore pressure and, consequently, slope stability. Some of this water is lost through evaporation and plant transpiration, collectively termed actual evapotranspiration (ET). Potential evapotranspiration (PE) depends on climatic factors such as temperature, humidity, wind speed, and solar radiation, while actual ET is influenced by PET, soil moisture availability, and vegetation characteristics.

Net infiltration (NI), the water remaining after evapotranspiration and runoff, is crucial for soil water storage and slope stability. It can be calculated as follows:

NI = P − AE − AT − RO = P − ET − RO

(1)

where NI is net infiltration (mm/day), P is precipitation (mm/day), AE is actual evaporation (mm/day), AT is actual transpiration (mm/day), ET is evapotranspiration (mm/day), and RO is runoff (mm/day).

Potential evaporation (PE) represents the maximum evaporation rate under unlimited water availability and depends on thermal energy and atmospheric transport of water vapor [48]. Actual evaporation (AE) decreases as soil dries due to increasing soil suction, while transpiration (AT) refers to water loss through plant stomata. Together, AE and AT constitute actual evapotranspiration (ET).

Water runoff significantly influences net infiltration (NI), soil water storage, and slope stability. It refers to the portion of precipitation that flows across the surface instead of infiltrating the soil. Increased runoff reduces infiltration and soil water storage, directly affecting slope stability by decreasing water availability for resisting erosion and failure. Runoff is affected by factors such as precipitation intensity, soil permeability, vegetation, slope steepness, and urbanization. Heavy rainfall, impermeable soils, and impervious surfaces increase runoff, while vegetation slows it and improves infiltration. Saturated soils also contribute to higher runoff. While reduced infiltration can lower hydrostatic pressure and improve slope stability, excessive runoff may cause erosion, weakening soil and increasing the risk of failure. Effective runoff management is crucial to balance water storage and slope stability.

Cohesion in soils, particularly clays, arises from electrochemical bonds and capillary forces. These bonds weaken as the water content increases because matric suction is reduced, leading to a decrease in cohesion. When soil becomes fully saturated, water acts as a lubricant between particles, significantly lowering cohesion. Drying processes can temporarily increase cohesion through hardening, but long-term chemical interactions, such as mineral dissolution, may result in a permanent reduction in cohesion.

The internal friction angle, which depends on particle interlocking and friction, decreases with increasing water content. A higher water content leads to excess porewater pressure, reducing effective stress and shear strength. Over time, prolonged shear deformation may cause particle rearrangement, further lowering the friction angle.

Pratama et al. [49] conducted a study to evaluate the changes in unsaturated soil parameters, i.e., suction, cohesion, and internal friction angle, at different degrees of saturation. The results of this study, used to determine the relationship between saturation, cohesion, and soil suction, are crucial to understanding the mechanism of slope failure. The shear strength parameters of soil samples were examined using a direct shear test method. The results of shear tests indicate how increasing the degree of saturation reduces the soil suction and shear strength parameters.

Soil permeability changes with saturation levels and matric suction. Van Genuchten [50] introduced mathematical models to describe these variations, which depend on soil saturation and the suction pressure within the soil matrix. These models are essential for predicting how water moves through unsaturated soils, a critical factor in slope stability analyses.

As water infiltrates, soil suction decreases, causing a reduction in the effective hydraulic conductivity. This dynamic relationship governs the infiltration rate, water storage, and the distribution of pore pressure, all of which significantly impact the stability of slopes.

5.5. Conventional Measures, Nature-Based Solutions (NbSs), and Hybrid Solutions (NHbSs)

Slope instability prevention and landslide remediation can be effectively addressed using nature-based solutions, hybrid approaches, and traditional engineering techniques (see

Table 6. Typical NbS approaches and benefits.

NbS	Description	Benefits
Revegetation	Planting native vegetation to stabilize the soil.	Plant roots absorb water, improve soil structure, and reduce the risk of erosion and landslides.
Bioengineering Techniques	Using natural materials combined with vegetation (e.g., live stakes, coir mats, and brush layers) to stabilize slopes.	Enhance slope resistance to erosion, promote vegetation growth, and provide both immediate and long-term stabilization.
Terracing	Creating stepped levels on slopes to reduce runoff and soil erosion.	Slows water flow, improves water absorption, and decreases the likelihood of soil saturation and landslides.
Check Dams (Small Barriers)	Constructing small barriers made of natural materials across gullies or slopes to slow water runoff.	Retains sediment, reduces erosion, and promotes organic matter accumulation and vegetation growth.
Erosion Control Mats	Installing biodegradable mats made from natural fibers.	Mats allow vegetation to grow, enhance surface stabilization, and control erosion.
Natural Drainage	Implementing measures to improve drainage in landslide-prone areas.	Reduces water accumulation, soil saturation, and the likelihood of landslides.
Reforestation and Afforestation	Planting trees in deforested or degraded areas to restore ecosystems.	Tree roots improve soil stability, enhance water retention, and reduce landslide risks.
Riparian Buffers	Creating vegetated zones along waterways and slopes.	Reduce sediment runoff, prevent bank erosion, and protect water quality.
Slope Reshaping and Stabilization	Reshaping slopes to a more stable angle and reinforcing with vegetation and organic materials.	Minimizes the risk of landslides by reducing steepness, enhancing stability, and encouraging vegetation cover.
Slope Stabilization and Erosion Control	Techniques like revegetation and soil bioengineering to stabilize slopes.	Reduces erosion, promotes vegetation growth, and mitigates instability.
Disaster Risk Reduction	Forest barriers and river restoration to manage landslide and flood risks.	Provides natural defenses against disasters, reducing the impacts of floods and landslides.
Water Management	Wetland restoration and floodplain conservation for improved water retention.	Enhances water storage capacity, mitigates flooding, and maintains ecosystem functions.
Climate Adaptation	Agroforestry and ecosystem restoration to boost climate resilience.	Improves soil stability, enhances ecosystem services, and helps communities adapt to climate change.
Biodiversity Conservation	Protected areas, rewilding, and invasive species control to safeguard habitats.	Maintains biodiversity, protects ecosystems, and supports resilience.
Sustainable Livelihoods	Eco-tourism and sustainable farming to balance development with conservation.	Strengthens local economies, promotes community engagement, and ensures sustainable use of natural resources.

). Each of these sets of methods offers unique advantages and limitations, with the selection often influenced by site-specific factors, the severity of landslide risk, and the intended ecological and social objectives. A holistic approach that integrates these strategies can result in more robust and sustainable solutions for mitigating landslide hazards.

Conventional engineering approaches to slope stabilization and landslide mitigation predominantly focus on technical and structural methods. These rely on physical materials and established engineering practices to deliver immediate and reliable results. Such solutions are typically designed to ensure slope stability using well-tested techniques.

However, while these methods are effective in the short term, they often fail to address the root causes of instability and disregard ecological considerations. Conventional approaches tend to have a higher ecological impact and frequently require ongoing maintenance to sustain their effectiveness. Although they provide rapid stabilization, their alignment with long-term ecological sustainability goals is limited.

Nature-based solutions (NbSs) aim to enhance resilience and sustainability in mountain communities and ecosystems. They address challenges like landslides and floods, promote climate adaptation, conserve biodiversity, and support ecosystem services such as water purification and flood regulation. NbSs are cost-effective, require minimal maintenance, and offer co-benefits like carbon sequestration.

Hybrid solutions (NHbSs) combine the strengths of conventional engineering techniques and nature-based approaches, creating integrated systems that address the complexity of geotechnical challenges while promoting ecological sustainability. By blending engineering methods with natural processes, hybrid solutions leverage the immediate effectiveness of conventional methods alongside the long-term benefits of nature-based solutions (NbSs), ensuring more resilient outcomes for slope stabilization and landslide risk management. This multi-faceted approach, involving conventional engineering, NbSs, and hybrid strategies, offers a holistic framework for mitigating slope instability and landslides. By considering both ecological and engineering perspectives, stakeholders can develop comprehensive strategies that enhance the resilience of mountainous regions, promoting sustainable development and environmental stewardship.

Table 7. Geotechnical measures for slope stability and possible approaches.

Measures	NbS	NHbS	Gray	Comments
Hydroseeding, turfing, trees	✔			They are primarily NbSs. Can become NHbSs when combined with gray solutions, such as irrigation systems or infrastructure.
Fascines/brush	✔	✔		An NbS if made with natural materials. Becomes an NHbS when combined with artificial elements like meshes or other gray infrastructure.
Geosynthetics	✔	✔	✔	Geosynthetics are artificial materials.
Substitution/drainage blanket		✔	✔	If using only artificial materials, it is a gray solution. Can become an NHbS when combined with natural materials.
Riprap	✔	✔		An NbS if natural materials (e.g., sand) are used. Becomes an NHbS when combined with artificial elements (e.g., concrete structures).
Dentition			✔	It is a technical solution using concrete or other materials, so it is considered a gray solution.
Removal of (potentially) unstable slope mass		✔	✔	If the technical method does not involve natural processes, it is a gray solution. Combined with an NbS, it can be an NHbS.
Removal of loose, unstable rock blocks		✔	✔	A technical method without natural processes, thus a gray solution. Combined with an NbS, it can be an NHbS.
Removal of material from driving area			✔	Technical methods are gray when they do not use natural processes. Sometimes it is a temporary (urgent) solution.
Substitution of material in driving area			✔	Use of artificial materials for stabilizing the driving area, considered a gray solution.
Addition of material to the area maintaining stability		✔	✔	Artificial materials, like concrete or geosynthetics, are used for stabilizing the area, considered a gray solution.
Surface drainage works		✔	✔	Gray if artificial materials are used.
Local regrading to facilitate runoff			✔	Artificial method to reshape the terrain without integrating natural processes.
Sealing tension cracks			✔	Artificial materials used to seal cracks without natural elements.
Impermeabilization (geomembranes)			✔	Use of artificial materials to prevent water passage, without involving natural processes.
Vegetation–hydrological effect	✔			The use of vegetation to improve water balance and prevent erosion is an NbS.
Hydraulic control works		✔	✔	Artificial structures for controlling water flow are gray.
Shallow and deep trenches		✔	✔	Trenches filled with free-draining material are gray. Combined with an NbS, it can be an NHbS.
Sub-horizontal drains		✔	✔	Gray if artificial drainage is used.
Wells			✔	Use of artificial structures for water collection or control without involving natural processes.
Drainage tunnels, galleries			✔	Technical drainage systems without natural processes.
Vegetation	✔	✔		It is a natural solution.
Substitution		✔	✔	Substitution of material with artificial solutions can be an NHbS if it involves an NbS.
Surface or deep compaction			✔	Technical methods of surface compaction without natural elements.
Lime/cement mech. deep mixing			✔	Use of artificial materials like cement and lime to stabilize soil, considered a gray solution.
Grouting with cement or chemical binder			✔	Artificial binding materials used to stabilize the ground, considered a gray solution.
Jet grouting			✔	Use of artificial materials to improve soil stability without natural processes.
Modification of ground water		✔	✔	Artificial solutions to manage groundwater can be NHbSs if they incorporate NbSs.
Counterfort drains		✔	✔	Gray if artificial drainage systems are used.
Piles			✔	Use of concrete or steel piles for stabilizing soil considered a gray solution.

categorizes common geotechnical methods for slope stability and landslide remediation, distinguishing between NbSs, hybrid solutions, and traditional gray solutions, which rely on artificial materials such as concrete and metal.

6. Implementation of Climate-Adaptive Resilience Evaluation Concept

The CARE concept was applied to case studies of slopes that have experienced landslides. These case studies allowed for a rigorous evaluation of computational models by comparing simulations to real-world conditions. The locations were systematically selected to represent diverse types of slope instability and construction-related interventions, facilitating a comprehensive assessment of slope stability. This approach ensured that the models accurately reflected the observed conditions, improving their reliability.

The objectives of the analysis were (1) to evaluate the safety of slopes under climatic and anthropogenic stressors, (2) to identify preventive measures for mitigating landslides, (3) to propose rehabilitation strategies for areas where landslides have already occurred, and (4) to compare the effectiveness of nature-based solutions (NbSs), nature-based hybrid solutions (NHbSs), and gray solutions.

Characterizing potentially unstable slopes encompasses several key factors, including the location and affected area, slope type, and slope geometry. The area’s geology is fundamental, as geological properties such as rock type, structural features (faults and fractures), and soil composition critically influence stability. Weak, weathered rocks and clay-rich soils are especially susceptible to erosion and saturation, which heighten instability, while fractures and faults create weak zones that can precipitate slope failure. Climatic conditions are another crucial factor, with precipitation playing a central role.

Geomechanical properties, including cohesion, friction angle, and density, determine a slope’s resistance to sliding. Comprehensive geotechnical investigations are vital to assessing these properties accurately. External loads imposed by infrastructure such as buildings, roads, and traffic add significant stress to slopes, increasing the likelihood of failure if not adequately addressed during design and construction. Vegetation plays a stabilizing role by anchoring soil with its roots and mitigating erosion; however, deforestation or damage caused by wildfires can significantly diminish this stabilizing effect, leading to increased erosion and instability. Lastly, seismic activity, including earthquakes and tectonic movements, destabilizes slopes by loosening rock and soil, potentially triggering landslides, while tectonic processes over time create fault zones and fractures that further weaken slope integrity.

The case studies present integrated evaluations for slope resilience by applying the CARE concept. By analyzing diverse scenarios and interventions, the approach allows for the systematic evaluation of preventive, rehabilitative, and adaptive strategies. Comparisons of NbSs, NHbSs, and gray solutions enable the identification of optimal measures that balance ecological, economic, and engineering goals, thereby enhancing slope resilience against climatic and geological hazards.

Example of Landslides “Kebelj” in the Sub-Alpine Pohorje Mountains

This example illustrates the implementation of the CARE concept through a detailed step-by-step analysis, emphasizing the benefits associated with this methodology. Four scenarios—A, B, C, and D—were analyzed, with a more comprehensive discussion presented in Step 5 (Analysis of Slope Stability Under Rainfall Conditions).

Step (1) Slope Characterization

The presented example of the implementation of the CARE concept refers to a landslide in the Pohorje Mountains in Slovenia. Landslides occurred in early August 2023 after a period of intense and prolonged rainfall. This event affected a low-traffic local road characterized by a low-cost design tailored to its limited local use (see Figure 2). The affected infrastructure included both the road itself and utilities, such as a water supply line, electrical wiring, and telecommunication cables. The data for this case study came from the design project. This particular landslide was chosen as a case study as it represents a typical small landslide, which is one of the most common types, especially in suburban areas.

Resilience evaluation is an inherently multidisciplinary activity, engaging experts from diverse fields, such as geotechnical engineering, geology, seismology, hydrogeology, environmental engineering, engineering geology, and climatology. The integration of climate data is a significant aspect of this process.

Location and affected area—The study area is located in the Pohorje Mountains, Slovenia, with the geographical coordinates x = 46.40779, y = 15.44997. The investigated area is shown in Figure 3 and Figure 4. The landslide event affected an area of approximately 2000 m², damaging a local road and endangering a nearby residential house. The total area influenced by the landslide is estimated to be around 3000 m².

According to the landslide probability map, the site is situated within a region identified as having a high hazard for landslides. Initial field investigations were conducted to estimate the landslide’s depth, width, and length and to perform a visual assessment of its likely causes. The affected slope exhibits an average inclination of approximately 28°.

Geology of the area—The geological characterization of the area includes a comprehensive analysis of geological, geomorphological, seismological, and hydrogeological characteristics. An understanding of the geological conditions in this area was obtained from the geological map (Figure 4) and field geological surveys. The soil cover is composed of sandy clay of medium to heavy consistency. This 5 m thick layer lies on weathered marl, which becomes compact at a depth of 7 m. Seasonal variations and precipitation levels are known to influence soil saturation; however, information regarding the groundwater table remains unavailable.

Slope type and slope geometry—The slope was treated as a natural slope, including the excavation on the upper side of the road and a smaller embankment on the lower slope (Figure 5). The slope’s height, angle, and geometry were determined through geodetic measurements. It is a moderately steep slope located below the road, which itself exhibits a gentle ascent and generally follows the natural contours of the terrain.

Climatic characterization—The landslide site is situated at the boundary between the continental and Alpine climate zones. It was triggered by three consecutive days of intense rainfall in early August 2024.

Geomechanical description—The landslide is classified as a medium-depth landslide based on the Varnes classification system [37], with an estimated depth of approximately 6 m. It spans a width of 40 m and extends at least 50 m downslope. The break-off edge of the landslide runs along the road for a length of roughly 30 m.

Geotechnical investigation—Geotechnical investigations reveal that the soil profile at the site consists of distinct stratigraphic layers. The upper 3 m are sandy clay of light to medium density, transitioning to sandy clay of medium to heavy consistency, reaching a semi-solid state at 6 m. Below this, the substratum consists of marl.

The field investigation involved borehole drilling, soil sampling, groundwater level monitoring, and in situ tests such as standard penetration tests (SPTs). Laboratory tests, including soil classification, unit weight determination, direct shear tests, permeability tests, and oedometer tests, were performed to supplement field observations. Material properties critical to slope stability, such as cohesion, internal friction angle, density, and water content, were assessed. Increased water content was found to reduce shear strength and increase the slope material’s weight, contributing to instability. The geomechanical properties of the soil cover and bedrock are presented in

Table 8. Geomechanical parameters of the slope *.

Property, Symbols (Units)	Scenario *	Sandy Clay	Weathered Marl	Marl	Counterforts	Stone Ribs	Gravel Fill
Saturated unit weight γ (kN/m3)	A	18.5	19	23
	B	18.5	19	23
	C	18.5	19	23	22
	D	18.5	19	23		24	22
Effective cohesion c′ (kPa)	A	4	10	100
	B	4 (5)	10	100		0
	C	4	10	100	0
	D	0	0	100		100	1
Effective friction angle Φ′ (°)	A	24	28	45
	B	26	28	45
	C	24	28	45	35
	D	≤20	≤20	45		45	35
Saturated permeability ky = kx (m/s)	A, B, C, D	1·10−6	1·10−6	5·10−10	1·10−4	1·10−5	1·10−4
Volumetric water content VWC = Vw/Vs (-)	A, B, C, D	0.4	0.2	0.005
Compressibility mv (1/kPa)	A	5·10−4	5·10−4	1·10−7
	B	5·10−4	5·10−4	1·10−7
	C	5·10−4	5·10−4	1·10−7	1·10−5
	D	5·10−4	5·10−4	1·10−7		1·10−8	2·10−5

* A, B, C, and D represent different scenarios of analyses.

, with the soil model incorporating the peak friction angle and the zero dilation angle. The water retention curve for the sandy clay layer was determined using the Van-Genuchten [50] method, and permeability as a function of matric suction was obtained.

Step (2) Climate Threats

The impacts identified in step 1 and threats such as climate threats, land use changes, natural resource over-exploitation pollution, waste, invasive species, infrastructure and traffic, energy development, ecosystem shifts, loss of ecosystem services, and economic impacts must be considered so that the criteria for these threats will be met.

To integrate climate change considerations into the geomechanical model, projections of future climatic conditions at the site were included. Specifically, precipitation patterns were assessed based on the RCP4.5 climate change scenario, which assumes a substantial reduction in greenhouse gas emissions. Under this scenario, extreme precipitation events are projected to increase by 7% over the next 50 years [26,51], highlighting the need to account for intensified climatic stressors in slope stability analyses.

A preliminary climatic characterization of the landslide area, located in a continental climate zone, highlights that the key climate threat is rainfall. Figure 6 shows temperature and precipitation data recorded at the Ritoznoj Station (514780), from the beginning of July to the end of August 2023 [52]. This excessive rainfall likely contributed to the instability of the slope.

Step (3) Effects

Based on measured climate data, the corresponding climate effects can be identified as increased saturation, an increase in water infiltration, degradation of material strength due to increased saturation, increased seepage capacity and physical weathering, and increased surface and groundwater level and flow, including porewater pressure.

Step (4) Interface

The conversion of geological and climatic data into appropriate geomechanical parameters is a critical step for geomechanical analysis. In this case, water network infiltration (NI), i.e., the water remaining after evapotranspiration and runoff, was evaluated. Precipitation data were obtained from the Ritoznoj Station (514780), located near the landslide site. Figure 6 illustrates the multi-day average precipitation recorded during the landslide event in August 2023. A projected 12% increase in precipitation over the next 50 years, attributed to climate change, was incorporated into the analysis. It was assumed that processes such as water runoff, evaporation, and transpiration will occur on the slope. Based on these assumptions, the average net surface water infiltration was estimated at three levels: lower (optimistic), medium, and upper (pessimistic) values. These correspond to 0.5 mm/day, 13 mm/day, and 15 mm/day, respectively, or, equivalently, 0.579 × 10⁻⁷ m³/m²/s, 1.504 × 10⁻⁷ m³/m²/s, and 1.736 × 10⁻⁷ m³/m²/s. These infiltration values were subsequently used in geomechanical analysis.

Step (5) Analysis of Slope Stability Under Rainfall Conditions

The Eurocode standards, specifically Eurocode 7 [45], according to which the service life to be considered for ordinary performance levels is 50 years [46], and local technical specifications and the Manual for the Implementation of Geotechnical Investigations [53] were considered during the analysis.

The geotechnical model was developed by integrating the outcomes of climate change modeling into the analytical framework. A finite element method (FEM) seepage model was constructed, featuring a mesh of 0.5 m × 0.5 m elements to achieve high-resolution simulation accuracy. In the FEM, triangular elements adapt to complex geometries, while quadrilateral elements offer better accuracy and convergence. Their combination ensures efficient meshing, adaptive refinement, and stable simulations. The boundary conditions were carefully defined: the upper boundary simulates rainfall infiltration, the bottom boundary is treated as impermeable, and the right boundary is designed to allow water drainage. Figure 7 illustrates the model, presenting both the current conditions and projected scenarios under future climatic influences.

Using the Van Genuchten–Nielsen method [54], the soil–water characteristic curve (SWCC) of the slope was derived, followed by the determination of the permeability function curve. The results show that hydraulic conductivity decreases with increasing matric suction, while matric suction decreases with increasing volumetric water content (VWC). Consequently, VWC emerges as a critical parameter influencing both matric suction and hydraulic conductivity.

The variation in the slope’s safety factor during rainfall events was analyzed through finite element method (FEM) numerical modeling. Surface water content and porewater pressure changes during the infiltration process were evaluated using the SEEP/W module within the GeoStudio software v8.14 suite. SEEP/W models water flow in both saturated and unsaturated soils, offering robust simulations of seepage behavior. The SLOPE/W module, a two-dimensional limit equilibrium modeling tool, was employed for slope stability analysis. It provides extensive capabilities, including modeling porewater pressure and rapid drawdown, and supports a wide range of material behavior models. A notable advantage of SLOPE/W is its built-in unsaturated shear strength models, which enable effective modeling of unsaturated soils. However, SLOPE/W does not simulate progressive slope failure caused by successive shrink–swell cycles.

For this study, the upper surface was designated as a boundary for rainfall infiltration, assuming all rainwater infiltrates at the onset of the event. The bottom boundary was set as nearly impermeable, while the right boundary allowed for water drainage. Infiltration depth was influenced by the stratigraphic configuration, constrained by the impermeable rocky base. The simulation covered five days, beginning with the initial rainfall event. The groundwater level is shown by a blue dashed line, with water drainage facilitated through the right boundary.

Different scenarios of the slope stability analysis are considered: Scenario A, which represents slope stability without any intervention; Scenario B, which evaluates stability with the implementation of preventive measures using NbS measures; Scenario C, assessing stability with the implementation of preventive measures using NHbS measures; and Scenario D, which evaluates slope stability after remediation following a landslide event, using a gray solution or an NHbS solution when possible.

Scenario A—Slope stability without remediation

To evaluate the computational model, an analysis of the state before remediation was performed, when the slope actually collapsed, and the computational scenario should match the actual events. Based on the stability analysis, the following results were obtained for the safety development factor over time by LEM analyses for the current and future scenarios without remediation. Current and future scenarios were calculated for the case of increased precipitation over the next 50 years. This would be considered if the safety factor was satisfactory, i.e., SF ≥ 1.3.

The analysis was carried out for lower, medium, and upper values of net infiltration, which were chosen so that the values of net infiltration for the current and future climate scenarios lay between the lower and upper values.

Table 9. Safety factor over a time of rainfall, without remediation.

Time (Days)	Without Remediation, NI = 0.5794 × 10−7 m3/s/m2	Without Remediation, NI = 1.157 × 10−7 m3/s/m2	Without Remediation, NI = 1.736 × 10−7 m3/s/m2
0	1.119	1.119	1.119
1	1.112	1.091	1.060
2	1.058	1.004	0.964
3	1.011	0.956
4	0.984
5

shows the safety factor at the beginning of intense rain and the time changes in the safety factor with several days of intense rain. The results show that, according to the EN1997 standard [45], the safety factor is too low at the beginning of intense rain and that on the third or fourth day the slope collapses. This also corresponds to actual events.

Figure 7 shows the geometry and mesh of the numerical model of the slope, the model, the computed water flow within the slope, and the critical failure line with the safety factor at the beginning of rainfall and after 5 days of rainfall.

Scenario B—Slope stability with NbS preventive measures

Surface water runoff in road and counterfort drains serves as a drainage mechanism for both surface and groundwater on slopes. A perforated collector pipe, installed at the base, facilitates the collection of water and ensures its efficient removal from the slope. This helps mitigate the risk of increased pore pressures that could destabilize the slope. Counterfort drains are widely used as emergency remedial measures for landslides. In this analysis, the effectiveness of counterfort drains in enhancing slope stability was evaluated. Multiple stability analyses were conducted to isolate and assess the specific functions of the counterfort drain.

Water infiltration rates were modeled to represent future scenarios, and the impact of collector pipes was investigated under conservative assumptions. These assumptions included maintaining the soil’s properties consistent with sandy clay without accounting for any improvements in shear strength or increases in permeability due to replacing the soil with rock fill.

The analysis revealed distinct stability trends over a five-day period. In scenarios where only the drainage collector was installed without modifications to shear strength, the stability factor began at 1.195 and progressively decreased.

Table 10. Safety factor over a time of rainfall with preventive NbS remediation without modifications to shear strength.

Time (Days)	Without Remediation, NI = 0.5794 × 10−7 m3/s/m2	Without Remediation, NI = 1.157 × 10−7 m3/s/m2	Without Remediation, NI = 1.736 × 10−7 m3/s/m2
0	1.195	1.195	1.195
1	1.141	1.106	1.071
2	1.071	1.022	0.982
3	1.038	0.986
4	1.019
5	1.015

presents the safety factor at the onset of intense rainfall and tracks its variation over several days of heavy rain, assuming that only the permeability of the buttress drains was improved while the shear strength of the soil remained unchanged. The results indicate that, according to the EN1997 standard [45], the safety factor remains insufficient over time unless shear strength improvements are incorporated into the rehabilitation strategy.

Assuming that shear strength improves over an extended period, the stability trends over the five-day analysis period become more distinct. In scenarios where a drainage collector was installed and the long-term shear strength of the sandy clay layer increased, the stability factor initially measured 1.158 and gradually declined.

Table 11. Safety factor over a time of rainfall, with preventive NbS remediation, under the assumption of improved shear strength in the clay layer.

Time (Days)	Without Remediation, NI = 0.5794 × 10−7 m3/s/m2	Without Remediation, NI = 1.157 × 10−7 m3/s/m2	Without Remediation, NI = 1.736 × 10−7 m3/s/m2
0	1.275	1.275	1.275
1	1.212	1.179	1.146
2	1.139	1.095	1.058
3	1.107	1.060	1.021
4	1.088	1.036	0.999
5	1.084	1.030

presents the safety factor at the start of intense rainfall and its progression over several days of heavy rain under the assumption of improved shear strength (cohesion from 4 kPa to 5 kPa) in the clay layer. The findings indicate that, according to the EN1997 standard [45], the safety factor remains insufficient over time unless a significant improvement in shear strength occurs.

Figure 8 shows the critical failure line with the safety factor after 3 days of rainfall, assuming preventive measures with drainage.

Scenario C—Slope stability after NHbS remediation

In this scenario, surface water drainage from the roads is enabled. A perforated collection pipe is built into the base, which allows water to be collected and ensures that water is drained from the slope as quickly as possible to prevent the possibility of increased pore pressure. In addition, the counterforts are filled with rock fill and are designed as stone ribs. In this analysis, the increased stability was assessed, including the effect of the stone rib. Several stability analyses were performed, with water infiltration corresponding to the future climate scenario.

The pressure is reduced to zero on the underside of the stone rib. If the drainage works, the shear strength will improve over time. The calculation assumes that this has not yet occurred and only the permeability of the supporting drains increases, while the shear strength remains the same as before the rehabilitation. In such a case, the backfill between the stone rib and the road is important. The calculated stability starts with a safety factor of 1.333 and remains constant over time. This fulfills the requirements of the Eurocode standard.

Figure 9 shows the geometry and mesh of the numerical model of the slope and the critical failure line and safety factor after 3 days of rainfall for the future climate scenario.

Scenario D—Slope stability after remediation

If a landslide has already occurred, landslide rehabilitation is required. The analysis should take into account that the soil material in the landslide area has collapsed and has significantly lower shear parameters. When the thickness of the soil layer is too large, a supporting structure, such as a pile wall (a gray solution), is required.

However, if the soil layer is thin enough (usually 5 m or less), a stone supporting structure can be implemented in combination with NbS measures. For a specific calculation example, this also means replacing the soil material between the supporting structure and the road.

In this scenario, surface water drainage from the roads is enabled. A perforated collection pipe is built into the base, which allows water to be collected and ensures that water is drained from the slope as quickly as possible to prevent the possibility of increased pore pressure. In addition, the counterforts are filled with rock fill and are designed as stone ribs. In this analysis, the increased stability was assessed, including the effect of the stone rib. Several stability analyses were performed, with water infiltration corresponding to the future climate scenario.

The pressure is reduced to zero on the underside of the stone rib. If the drainage works, the shear strength will improve over time. The calculation assumes that this has not yet occurred and that only the permeability of the supporting drains increases, while the shear strength remains the same as before the rehabilitation. In such a case, the backfill between the stone rib and the road is important. The calculated stability starts with a safety factor of 1.33 and remains constant over time. This fulfills the requirements of the Eurocode standard.

Figure 10 shows the geometry and mesh of the numerical model of the slope and the critical failure line with the safety factor for the future climate scenario.

Analysis findings

The proposed solution to address the landslide problem involves conducting timely stability analysis, including an interface study on the effects of planting with reduced water network infiltration, the effects of drainage, and interventions for water runoff on the road and its surroundings.

The analysis shows that slope stability cannot be guaranteed, even without taking climate change into account. Preventive measures, including nature-based solutions (NbSs), such as planting and water runoff on the road, or nature-based hybrid solutions (NHbSs), such as drainage systems reinforced with stone material, provide sufficient safety while taking into account the effects of climate change. However, if a landslide has already occurred, remedial measures are required that use retaining structures as part of gray solutions or NHbSs.

7. Conclusions

Land management is a cornerstone of both mountain and slope resilience, offering a pathway to enhance the health of mountain ecosystems and their ability to recover from disturbances. Sustainable land management strategies are essential for addressing the geotechnical challenges posed by climate change and ensuring long-term resilience. This paper introduces a structured approach to evaluating and strengthening the resilience of mountainous environments, emphasizing the importance of timely evaluation and targeted measures. The proposed conceptual framework outlines a causal chain—land area characterization, resilience threats, effects, and consequences—that serves as a guideline for risk assessment and sustainable management. Land characterization encompasses the type, surface, and properties of land, along with its technical and biotic aspects and specific resilience challenges. Resilience threats are analyzed based on their effects and the complex interrelations that lead to specific consequences. Without thorough analysis and proactive measures, these consequences can be unpredictable, underscoring the necessity of a structured, systematic approach to resilience evaluation and adaptation.

The CARE concept represents a significant advancement in geotechnical analysis by introducing an innovative interface that translates climate signals and effects into input parameters suitable for geotechnical evaluation. Geostructures, characterized by substantial geomechanical variability, are traditionally analyzed using established methods that often fail to incorporate the impacts of climate change. The interface addresses this limitation by integrating climate data and converting them into parameters that support precise and context-sensitive analyses. This methodology is illustrated through a case study on slope stability, highlighting its practical application in mountain resilience.

Tailored to the unique challenges of mountainous environments, the CARE concept emphasizes both slope stability and the integration of climate resilience and adaptation strategies. While grounded in technical considerations such as safety and functionality, it also addresses broader resilience objectives. A critical challenge in applying the framework lies in determining the interface parameters. The multidisciplinary nature of the required data—encompassing climatology, agronomy, and geology—necessitates close collaboration among experts from these fields. Such cooperation ensures that the data are accurate, comprehensive, and effectively aligned with geotechnical requirements.

Geotechnical planning follows a step-by-step process aligned with international standards [32] and incorporates strategies for achieving climate neutrality while mitigating the impacts of climate change. Therefore, special attention is given to nature-based solutions (NbSs), which are integrated with conventional geotechnical methods into hybrid solutions (NHbSs). Proposed stabilization measures for slopes are divided into preventive and corrective actions. Comparative analysis demonstrates that preventive measures, particularly those involving NbSs, are often sufficient and cost-effective. Conversely, once a landslide has occurred, conventional or hybrid measures are generally required for successful remediation.

Despite its strengths, this study acknowledges several limitations. The resilience framework and the CARE concept, while systematic, rely on existing climate models and geotechnical parameters that may not fully capture the dynamic interactions between climate variability and soil shear parameters. The complexity of mountainous environments, including heterogeneous soil properties and variable hydrological conditions, poses challenges in standardizing resilience assessments. Additionally, the integration of climate effects into geotechnical analyses requires extensive datasets, which may not always be readily available or accurately reflect real-world conditions.

Another limitation is the uncertainty associated with climate projections and their localized impacts on soil stability. Variability in precipitation patterns, temperature fluctuations, and extreme weather events can lead to unpredictable changes in soil moisture content and pore pressure, significantly affecting shear strength. While the CARE concept provides a structured methodology, further refinements are needed to enhance its predictive capabilities and adaptability across diverse geotechnical settings.

To address these limitations, future research should focus on laboratory investigations aimed at quantifying the correlations between climate effects and soil mechanical properties. Specifically, experimental studies should explore the relationships between degree of saturation, moisture content, stress conditions, and pore pressure in different soil types under controlled conditions. Such studies would provide empirical data to refine geotechnical models and improve the accuracy of resilience assessments.

Moreover, advanced numerical modeling techniques should be developed to simulate the long-term effects of climate change on shear parameters.

Interdisciplinary collaboration remains crucial in advancing resilience strategies. Future studies should integrate insights from environmental science, hydrology, and geotechnical engineering to develop comprehensive solutions for mitigating landslide risks. By incorporating both preventive and corrective measures, particularly nature-based solutions (NbSs) and hybrid approaches, geotechnical planning can be further optimized to enhance land resilience in climate-sensitive regions.

Ultimately, continued research and innovation will be key to strengthening the resilience of mountainous landscapes and ensuring sustainable land use practices. By refining analytical frameworks, improving predictive models, and leveraging technological advancements, the long-term safety and stability of slope environments can be significantly enhanced.