Assessment of the Effectiveness of Green Infrastructure Interventions to Enhance the Ecosystem Services in Developing Countries

Abstract

Cities face complex challenges, including climate change, population growth, urbanization, natural hazards, pollution, biodiversity degradation, and inadequate public services. Hydro-meteorological hazards such as floods, landslides, droughts, and heat waves are among the most significant risks, with floods often causing severe impacts and loss of life. Traditional responses, typically hard engineering infrastructures, dominate mitigation efforts. However, green infrastructures (GIs) offer sustainable, cost-effective solutions with added benefits, enhancing ecosystem services and societal well-being. Despite their effectiveness, GI implementation is slow, particularly in developing countries, due to the complex construction, operation, and maintenance processes, alongside knowledge gaps. This study proposes an assessment framework to evaluate GI performance in mitigating hydro-meteorological hazards. By integrating hydrologic–hydraulic modeling, the framework analyzes baseline and post-intervention conditions, offering valuable insights into hazard reduction and cost-effectiveness. Key indicators for assessing GIs include runoff volume reduction, peak flow reduction, flood node mitigation, and increased time to peak flow. Studies show that GIs can achieve reductions of 30–90%. This framework aims to advance the adoption of GIs by providing practical tools to assess and monitor its performance in hazard management.

1. Introduction

Cities are dynamic and complex frontlines, facing a myriad of complex and interconnected challenges, including the impacts of climate change, population growth, urbanization, pollution, and socioeconomic inequities [1]. Natural hazards increase this complexity and disrupt urban systems, owing to a lack of urban planning, inefficient governmental institutions, inadequate water public services, and a lack of technical knowledge and political will. Therefore, they are vulnerable to disaster, with increasing risk areas and decreasing urban resilience and sustainability [2].

According to [3], it is understood that an urban system is an ecosystem arranged into four subsystems: decision makers (government and non-government institutions), materials and energy produced and consumed, urban infrastructure, and socioeconomic dynamics. Resilience is the capacity of urban systems to resist, adapt, maintain, and restore their normal condition after the occurrence of threats [4]. Urban sustainability encompasses the management and enhancement of the system, considering the needs of future generations [5].

Cities are exposed to unplanned population growth, which has led to an increase in the rate of urbanization [6]. According to the World Cities Report 2022 of the United Nations, 68% of the world's population will live in urban areas by 2050. However, in low-income countries, this number is increasing faster, making it a great challenge to develop sustainable and resilience cities that can face social, economic, and environmental crises [7]. A large proportion of the world’s population depends on the socioeconomic conditions of cities [8]. In developing countries, adverse impacts include a decline in green urban areas, and issues related to deficient basic public services, e.g., the water supply, as well as sanitation, pollution, and hygiene [9].

Furthermore, accelerated urbanization has a straightforward impact on increasing the surface runoff volume by changing land use and expanding impervious areas, which is more harmful than the effects of climate change, as stated in [10]. The results obtained in this research over 30 years show that runoff volumes increased by 140% due to urbanization, while an increment of 48% was reached due to climate change. The consequence of this is urban flooding, which is probably one of the most devastating forms of natural disaster in the world.

Rapid demographic growth and urban construction are the main driving forces that degrade the performance of urban drainage systems, leading to strong modifications to the parameters of the hydrologic cycle [11]. Infiltration, concentration time, water quality, and base flow decrease, while flow velocity, runoff coefficient, and runoff volume significantly increase [12]. Surface runoff has increased due to land use and land cover dynamics. If this dynamic pattern continues, the risk of flooding will worsen; thus, government institutions must apply sustainable solutions to mitigate it [13].

Stormwater runoff is a crucial and widespread environmental issue that governments or municipalities are dealing with [14]. The total precipitation that falls to the ground either infiltrates the soil or evaporates, and depending on the soil saturation, it can flow to the surface. However, as terrain that is more natural forms an impermeable area, total precipitation is transformed into net rainfall, meaning that a greater amount of volume of surface runoff enters the sewer system or traditional grey stormwater infrastructure [15]. Thus, stormwater management must take into account not only the water quantity but also the water quality to ameliorate pluvial and fluvial flood risk [16].

To cope with an inflow of stormwater that exceeds the hydraulic capacity of the urban drainage system, traditional management has focused on the hard engineering infrastructure (upsizing conduits, expanding pumping systems, and building storage tanks and additional pipes) to convey flows as quickly as possible to places away from developed areas [17].

Cyclones, earthquakes, and tsunamis are natural hazards that can cause damage to people and property [18]. Hydro-meteorological hazards, like floods, droughts and landslides, are the most significant natural disasters [19]. However, floods are the most damaging of all natural hazards in urban areas in the world, producing different types of impacts, which can be physical, economic, social, environmental, short and long term, tangible, and intangible [20]. Figure 1 depicts the social and economic impacts related to flood hazards and improper water and sanitation services according to the report of the United Nations [21].

The undesirable impacts owing to climate change, urbanization, and human population, have been increasing awareness about the need to minimize their consequences by employing a different approach, whose main components are natural elements [22]. Urban planners or government institutions are looking for proactive strategies to overcome political, social, and environmental pressures to reframe urban resilience and sustainable cities [23]. In addition to flood risk, aspects of regeneration, reuse, water treatment, recover, recreation, amenity, ecology, ecosystem services [24], biodiversity, air quality, regulating building temperature, water and energy savings, physical and mental health, also known as co-benefits must be analyzed [25].

Maryland (USA) was a pioneer in implementing sustainable solutions, and this stormwater management philosophy to minimize the impacts of urbanization and climatic change was called low-impact development (LIDs) [17]. The time evolution of the terminology of this discipline that takes into account natural processes is illustrated in

Table 1. Sustainable solutions and evolution terminology.

Sustainable Solution	Country	Year	Source
Low-impact development (LIDs)	US—New Zealand	1977	[26]
Best management practices (BMPs)	US—Canada	1980
Water-sensitive urban design (WSUD)	Australia	1994
Green infrastructure (GI)	US—UK	1995
Sustainable urban drainage systems (SuDs)	UK	2001
Nature-based solution	Europe	2008
Ecosystem-based adaptation (EbA)	Canada—Europe	2009
Ecosystem-based disaster risk reduction (Eco-DRR)	Europe—US	2010
Blue–green infrastructure (BGI)	UK	2013
Ecosystem services (ES)	Europe	2015	[27,28]
Natural Water Retention Measures	Germany	2016	[28]
Ecological Engineering (EE), Natural Capital (NC)	UK	2017	[29]
Natural Climate Solutions (NCS)	USA	2017	[30]
Eco-engineering solutions	UK	2020	[31]
Building with nature (BwN)	The Netherlands	2021	[32,33]
Natural flood management (NFM)	UK	2022–2024	[34,35]
Natural Water Retention Measure (NWRM)	European Union	2024	[36]

.

Green infrastructures (GIs) are innovative solutions that use natural materials, soil and local vegetation [23]. They operate in conjunction with forests, agricultural lands, rivers, wetlands, and parks, whose main objectives are to improve social, and environmental conditions, economic opportunities, and biodiversity [37]. GIs can be applied not only for water management by mitigating flood risk and enhancing urban resilience, but also for multiple benefits for society, finance and nature [38]—for example, a reduction in the urban heat island; optimization of energy efficiency by saving heating or cooling of buildings; prevention of soil erosion, improvement water and air quality; increment of properties values; promotion of biodiversity and species habitats; improvement of physical and mental health contributing to people’s happiness; reduction in noise pollution, stress, and the risks of cardiovascular diseases, diabetes, obesity [39].

There is a wide variety of GIs, classified according to their functions: flood volume control, water retention and detention, infiltration, water quality, erosion control, groundwater recharge, recreation, decreased urban heat island, and physical and mental well-being [40]. Figure 2 illustrates the most common GIs.

Conversely, grey or traditional engineering (pipes, tunnels, sub-catchments, gutters, manholes, levees, channels, pump stations, etc.) is the most appropriate solution to reduce flood volume [41]. These structural measures can reduce the flood volume by 27% according to [42]; however, these infrastructures are not sustainable solutions.

A holistic approach that encompasses broad benefits is called hybrid solutions, which integrate traditional grey infrastructures with sustainable green and blue techniques [43].

South America has the highest urbanization growth rate in the world, reaching 85% [44]. In addition to inadequate urban planning, it has prompted an urban heat island, flood risk, deficient provision of water, and sanitation, and deterioration of ecosystems [45]. Consequently, the use of GIs in Latin America is a primary need to contribute to sustainable urban planning.

There are several reports of GI implementation. In [46], a prototype of a grey–green combination was proposed to solve flooding and environmental pollution and to protect the riparian zone in Costa Rica. Similarly, in the same country, there is another investigation [47] that deals with socioecological benefits by employing a prototype NBS co-design framework to improve wastewater management, through cooperation between academia, municipality and the community.

Research carried out in Bogota, Colombia [48], to figure out the barriers to the application of sustainable urban drainage systems (SUDs) in developing countries, found six categories: cultural, financial, institutional, political, technical and urban.

Meanwhile, in Quito, Ecuador, an NBS implementation project [49] (gardens, green roofs, forestry, agroecological parks) was selected to address landslides, fires, flooding hazards, water provision, inadequate stormwater and waste water management, and pollution [48]. Several workshops were held with residents, to identify these problems [49].

One of the most important public services that has been aggravated by population growth and climatic change is the urban drainage systems, resulting in flash floods [50]. The characteristic of this natural disaster is a sudden increase in surface runoff, which worsens the performance of sewer systems. Therefore, to control stormwater runoff, alleviate the surcharge flow in the sewer systems, and ameliorate flood hazard, hybrid solutions have been proposed [20]. These structures that integrate grey and green approaches give more efficient results in flood management. However, grey engineering solutions, have some issues to take into account in their evaluation, aging and biochemical corrosion [51].

To overcome the challenges stated in the last paragraphs, it is vital to conduct robust and calibrated hydrologic–hydraulic models [52], which play a critical role in the analysis of the performance of hybrid approaches and the spatial implementation of GIs [53]. Several GI scenarios were evaluated by using 1D HEC-RAS and the GIS platform for flood mitigation [54], and one positive outcome was the reduction in flood risk in a range of 15–37%.

An urban drainage system (UDS) is necessary to preserve and promote public health, well-being, flood protection, water pollution, and economic development of any region [55]. The sewer system is an infrastructure to collect, transport and dispose the sewage, that is, the discharge of domestic, commercial and industrial water, as well as surface and groundwater [56]. This is essential infrastructure for the communities, and its rehabilitation represents a huge cost for local governments; its maintenance and rehabilitation, or corrective actions, are often neglected until catastrophic events happen [57].

Several factors can lead to the collapse of the sewer system, which is constantly subjected to physical, chemical, biochemical and biological stresses. The main factors are: [58] infiltration/exfiltration; flow obstacles; positional deviations; mechanical wear; corrosion; deformation; cracks; blockage in gullies; root penetration; poor sewer design; aging of its structures; improper maintenance [59].

Sewer systems, like all engineering works, do not last forever; they deteriorate over time and require subsequent maintenance and repair during their useful life [60]. If repairs and renovations are not conducted at the right time, the useful life is shortened with the risk of a dangerous collapse situation. Thus, the “Sewerage Rehabilitation Manual” [61] defined rehabilitation as the activity that covers all aspects of upgrading the performance of existing sewerage systems and includes repair, renovation and replacement. The “Sewerage Rehabilitation Manual” recommends some procedures to follow in the holistic evaluation of the performance of an existing sewer system [60], which are divided into several investigations: hydraulic, structural, environmental, operation, and social [62].

The increasing popularity of green infrastructures (GIs) all over the world is due to their capacity to protect, restore, and regenerate urban and natural ecosystems, providing social, economic, environmental and human well-being benefits [63]. Thus, it becomes increasingly crucial to evaluate the performance of GIs to understand its plan, design, implementation, operation, maintenance and monitoring. The main hypothesis of this article is that the development of the proposed methodological framework will allow us to overcome a great limitation and barriers that prevent the implementation of GIs in developing countries.

This paper aims to establish and identify methods, tools and indicators for assessing the effectiveness of green infrastructure for the benefit of urban resilience. For this purpose, a review of scientific articles was carried out, classifying them into twelve criteria as explained in the next item.

2. Methodology

The methodology of this study was structured in three phases as illustrated in Figure 3.

This research aims to analyze methods, tools, guidelines, and indicators to propose a framework to prove the effectiveness of GI impacts considering hydro-meteorological hazards. To do so, this research explores, reviews and finds official reports, relevant articles, and scientific journals with DOI (indexed in JCR or SJR), which are related to concepts, procedures, parameters, designs, modeling, barriers, stakeholders participation, guidelines, policies and regulations, criteria, indicators and results of implementation, effectiveness, and performance of green infrastructure (GI).

2.1. Phase 1: The Review Process

The first step of this study was conducted through a systematic review of the literature and retrieval of publications related to mitigation actions to enhance urban resilience based on nature, whose name has been changing thorough time and places.

The search query was performed using terms such as “Effectiveness of Nature-Based Solutions (NBS)” “Evaluation NBS” “Performance NBS” “Green Infrastructure GI” OR “Low Impact Development LIDS”, AND “Urban Drainage Management” AND “Flooding” AND “GI Indicators”.

The negative impacts of climate change, urbanization and demographic growth are affecting not only ecosystem services but also human well-being [64]. The action of GIs to improve urban resilience [65] results in several benefits—for example, reducing the impact of flooding and drought hazards, CO₂, energy and water consumption, and improving water and air quality, social, health and environmental conditions.

The authors of [66] argued the relevance of evaluating the functionality and benefits of GIs through the use of valuation tools. These tools support the decision of GI implementation projects by government and municipality personnel, and the corresponding financial support.

On the other hand, ref. [67] emphasizes the essentiality of developing key performance indicators not only in the design phase but also during the life cycle of GIs. These indicators must be understandable, comprehensive, relevant and realistic according to the study area, to develop the best strategies for operation, maintenance and asset management [68].

Indicators are understood to be qualitative or quantitative indices, which are crucial to evaluating the performance of a particular GI solution and must have specific metrics (measured values) [69].

The review aimed at deepening all the possible studies related to the assessment of the performance of GIs, owing to the multi-functionality and complexity of GIs, citizen interest, and wide goals, the scientific documents found must be grouped into different criteria [70].

To facilitate the analysis and classification of the documents collected, the summary data of this scientific material were inserted into a matrix. This matrix contains useful information to define several criteria—for instance, it includes country and year of publication, journal, aim, details of the study area, methodology, GI implementation, monitoring, results, tools used to assess the performance, benefits, limitations, and disservices. After the analysis of objectives, methodology, tools and results, the scientific works were filtered and grouped into twelve criteria.

The criteria were selected based on the characterization of GI services. For instance, the authors of [71] consider the cost–benefit of ecosystem services and social and environmental aspects. Meanwhile, the project [72] grouped 10 challenges into three categories: the “water” category contains climate mitigation and adaptation, water management, and coastal resilience. The “nature” category includes urban regeneration, air quality, and green space management. Finally, within the category of “people” are economic and green jobs, public health, social justice and cohesion, participatory planning and governance.

The criteria defined in this work are: urban drainage management; urbanization; climate change, urban regeneration; co-benefits; social–stakeholder participation; policy and regulation; modeling performance; urban resilience; economic assessment; monitoring and maintenance; and performance indicators (Figure 4).

2.2. Phase 2: Analysis of Criteria and Indicators

The publications found in the previous step under the fields mentioned were distributed in 41 countries (Figure 5).

The second part of the methodology was focused on the analysis of the scientific articles classified under the aforementioned criteria. This analysis consists of identifying the most representative indicators and the corresponding values obtained, which can be quantitative and qualitative. Determining appropriate indicators is a challenge due to the amplitude of GIs [73].

The methods and tools that are used to determine indicator values are hydrologic–hydraulic modeling of water dynamics, surveys, measurements by sensors, surveys, interviews, maps, remote sensing, geographic information systems, observations, laboratory tests, and cost–benefit analysis [74].

To implement GI projects, the biophysical and socioeconomic aspects of the area must be taken into account. Some steps are needed for planning, design, implementation, monitoring, assessment, management and evaluation, and these are: define the problem; develop financing strategy; develop GI management strategy; estimate cost–benefit-effectiveness; design the intervention; construct; monitor [74].

The process of designing, implementing, evaluating, maintaining and monitoring GIs, has various uncertainties. This can be improved by the participation of several actors, for instance personnel of industries, municipal and government technicians, academia, and residents, who are involved in the development and co-creation of GIs [75]. Some studies highlight the importance of supporting stakeholders to select indicators [76].

In this regard, the authors of [77] selected some indicators and calculated their values and grades based on meetings with stakeholders, which were tested in a study area.

These indicators are under three challenges: water, nature and people. Then, the indicators of water storage and reuse, flood mitigation, irrigation cost, resiliency, and water quality are classified under “water”. Meanwhile, infiltration, biodiversity, soil quality, and air quality are associated with “nature”. Finally, cultural and spiritual, economic and agricultural are related to the challenge “people”.

To determine the effectiveness of GI measures, the results of the evaluation methods and tools were used to compare the differences between scenarios with and without implementation of GIs. From these differences, values (0–100%), scores (1–5) and grades (very poor–excellent) for each indicator were generated. For instance, if the values of the indicators are below 40%, this means that the score is 2, then the grade is poor. Therefore, the implemented GI measure is not relevant to the purpose for which it was designed.

On the other hand, ref. [78] recommended some indicators classified into 12 categories: climate resilience (38 indicators), water management (53 indicators), natural and climate hazards (65 indicators), green space management (60 indicators), biodiversity enhancement (41 indicators), air quality (18 indicators), place regeneration (34 indicators), knowledge and social capacity building for sustainable urban transformation (14 indicators), participatory planning and governance (29 indicators), social justice and social cohesion (24 indicators), health and well-being (30 indicators), new economic opportunities and green jobs (50 indicators). These indicators can be used as a reference starting point, and their choice depends on the type of GI, financial resources, and the challenges that need to be addressed.

The most relevant indicators classified under those 12 categories [75] are summarized in

Table 2. GI indicators are classified under ten categories.

Category	Indicator	Reference
Climate Resilience	Heatwave incidence	[80]
	Human comfort: physiological equivalent temperature	[81]
	Urban heat island (UHI) effect	[82]
Water Management	Surface runoff	[83]
	Total suspended solids, nitrogen and phosphorus concentration or load	[84]
	Infiltration rate and capacity	[85]
	Height of flood peak and time to flood peak	[86]
Natural and Climate Hazards	Disaster resilience	[87]
	Heatwave	[88]
Green Space Management	Accessibility of green space, measured as travel time	[89]
Biodiversity Enhancement	Proportion of natural areas within a defined urban zone	[90]
Air Quality	Number of days during which atmospheric PM2.5 exceeds threshold values	[91]
Place Regeneration	Derelict land reclaimed for NBS	[92]
Participatory Planning and Governance	Consciousness of citizenship	[93]
	Perceived ease of governance of NBS	[94]
Social Justice and Social Cohesion	Participation of vulnerable or traditionally under-represented groups	[93]
Health and Well-Being	Hospital admissions due to high temperature during extreme heat events	[95]
New Economic Opportunities and Green Jobs	Mean land and/or property value in proximity to NBS	[96]
	Number of new jobs in the green sector	[89]

. To select the performance indicators, some aspects must be taken into account, e.g., type of problem, solution and scale to be solved; adaptation to the needs of local conditions; thresholds; stakeholders acceptance; policy regulations capability; and economy efficiency [79].

Meanwhile, ref. [19] defined areas, criteria, sub-criteria, and indicators, such as peak flow, total flow volume, and flooded area under the sub-criterion of flooding risk resilience. In addition to selecting the appropriate indicators, it is about estimating or calculating their values or metrics.

Indicator values can be used to determine whether GI implementation would achieve benefits. Some authors [69] have demonstrated GI effects of reducing outdoor and indoor temperatures of 2–2.5 °C due to the presence of green areas. Human comfort is related to acceptable temperature conditions, ref. [97] proposed the next thermal scale described in

Table 3. Thermal scale [69].

Scale	Description	Sensation
3	Hot	Intolerably warm
2	Warm	Too warm
1	Slightly warm	Tolerably uncomfortable, warm
0	Neutral	Comfortable
−1	Slightly cool	Tolerably uncomfortable, cool
−2	Cool	Too cool
−3	Cold	Intolerably cool

.

Indicators related to Flood Vulnerability are flood peak height, time to flood peak, and infiltration capacity [69]. They can be measured or monitored before and after the GI implementation through the use of weirs, orifices, flumes, level and velocity sensors, and by using hydrologic and hydraulic modeling for several flood events return periods (1, 2, 25, 50 and 100 years).

Another significant challenge is water quality. Among the most common indicators is: Dissolved Oxygen (DO), which is the oxygen requirement to support aquatic life. Nitrogen and phosphorous concentration and their different chemical formations [69]. The suggested limit values are shown in

Table 4. Limit values for DO, NO₂⁻, and PO₄³⁻ [69].

EU Directive	Unit	Guideline Value
Dissolved Oxygen (DO)
Freshwater Fish [2006/44/EC]—salmonids	mg/L O2	50% ≥9
Freshwater Fish Directive [2006/44/EC]—cyprinids	mg/L O2	50% ≥8
Shellfish Directive [79/923/EEC]	% O2 saturation	≥80
Nitrite (NO2−)
Freshwater Fish Directive [2006/44/EC]—salmonid waters	mg/L NO2−	≤0.01
Freshwater Fish Directive [2006/44/EC]—cyprinid waters	mg/L NO2−	≤0.03
Drinking Water Directive [98/83/EC]	mg/L NO2−	N/A
Phosphate (PO43−)
Freshwater Fish Directive [2006/44/EC]—salmonid waters	mg/L PO43−	≤0.2
Freshwater Fish Directive [2006/44/EC]—cyprinid waters	mg/L PO43−	≤0.4

.

Not only are technical indicators valuable in evaluating GI performance, but also social, policy, governance and regulation aspects should be considered as well.

In the case of the participatory planning and governance category [94], the indicators openness of participatory processes (OPP) and participatory governance refer to the stakeholder participation. Their interventions are immersed in the co-creation, co-design, co-implementation, and co-monitoring of GIs.

The participation processes are calculated from the following expressions:

$$\left({\displaystyle \frac{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{open} \mathrm{public} \mathrm{participation} \mathrm{processes}}{\mathrm{Population} \mathrm{of} \mathrm{city}/100000}}\right)\times 100$$

(1)

$$\left({\displaystyle \frac{\mathrm{No}.\mathrm{of} \mathrm{citizens} \mathrm{engaged} \mathrm{in} \mathrm{relevant} \mathrm{projects} \mathrm{in} \mathrm{a} \mathrm{given} \mathrm{year}}{\mathrm{The} \mathrm{total} \mathrm{population} \mathrm{of} \mathrm{the} \mathrm{city}}}\right)\times 100$$

(2)

Another co-benefit is related to the improvement of the economy of the city where the GI was implemented by the creation of new employment opportunities [93]. For instance, commercial activities are mainly sports, cleaning, maintenance, manufacturing, etc.

The new businesses and green jobs (NNGJ) generated can be calculated with the following expression:

$$\mathrm{NNGJ}=\left({\displaystyle \frac{\mathrm{Number} \mathrm{of} \left(\mathrm{new}\right) \mathrm{green} \mathrm{jobs}}{\mathrm{Total} \mathrm{number} \mathrm{of} \left(\mathrm{new}\right)\mathrm{jobs}}}\right)\times 100$$

(3)

As explained in this phase, there are a vast number of indicators depending on the categories; therefore, the most appropriate indicators and their benefits were adopted to match each selected criterion.

The following chapter describes the proposed framework, which contains the main indicators and their values obtained from the review process.

2.3. Phase 3: The Proposed Evaluation Framework, Indicators and Metrics

According to [39], despite the importance of GIs, and how this natural solution has gained popularity, the development of studies related to the effectiveness and efficiency of these infrastructures is insufficient [98].

The huge number of indicators found in the previous section could become overwhelming. Therefore, it will be recommended to select the most suitable GI according to the local or specific challenges and pressures to be addressed and identify potential indicators that allow us to assess the behavior of those natural solutions. The indicators should be relevant, recognized, reliable, and robust [99].

As stated in the first chapter, hydro-meteorological risks are the most devastating natural hazard for humans [100]. Together with policy regulations, social and environmental issues are the utmost important challenges that cities have to deal with. Moreover, there is a lack of risk assessment frameworks considering GIs [101].

Little attention has been paid to risk research in mountainous cities, where natural hydro-meteorological hazards are significantly amplified due to the growing population without appropriate urban planning [102]. On the other hand, peri-urban areas, the regions on the slopes of the mountains, with scarce populations can produce landslides, and GIs must be projected [103]. GIs will be projected not only to protect these areas but also to regenerate soils, vegetation, and rivers [104]. Thus, within the baseline analysis of the framework, according to the hydro-meteorological hazards of the study area, the appropriate GIs and indicators have to be considered.

Moreover, there is a lack of evidence about the implemented interventions of GIs in mountainous regions [105].

In this context, this study proposed an assessment framework with indicators to evaluate the behavior of GIs in dealing with hydro-meteorological hazards (floods, landslides, droughts, heatwaves). The proposed framework will contribute to social and environmental benefits considering the availability of policy and regulations to enhance urban resilience in mountainous regions.

It is vital to build up evidence of the GI co-benefits and thereby decrease the level of uncertainty related to the paucity of knowledge about GI performance.

The proposed framework (Figure 6) presented herein, requires different kinds of input data. These are temporal (rainfall, water levels, water flows, dry weather flows, evapotranspiration, concentration loads, sedimentology), spatial (sewer topology, demographic population, river network, land use, land cover, soil data, infiltration), and terrain (digital elevation model DEM, watershed characteristic such as delineation, slope, area, width) [106].

This basic information is the minimum data to implement the hydrologic–hydraulic modeling, which will be used to simulate surface runoff, conduit or river flow under unsteady and nonuniform flow, to obtain hydrographs, stream flows, flow velocity, flow depth, flooded area, depth and velocity.

The results obtained from hydrologic–hydraulic modeling will allow researchers, planners and practitioners to define the baseline (before the implementation of GI) of the study area. Consequently, these results provide support for adopting and building the appropriate combination of GIs or hybrid (grey–green solutions) and their spatial location.

However, to select the more effective approach, it will be required to analyze local needs, socioeconomic conditions, geology and geotechnical characteristics, availability or status of policies and regulations in establishing GI solutions [107]. The co-creation, and co-design need the support, engagement and participation of diverse groups of stakeholders [76].

Once the indicators are identified, they need to be quantified. There are different approaches to this calculation. The research of [19] developed a procedure normalized to a dimensionless scale, by contrasting indicator results with their maximum and minimum values, and then the score was calculated by weighting (based on stakeholder preferences and co-benefits).

Another practical approach is proposed by the authors of [77], who proposed some equations, which depend on the difference between results obtained in the study area with GI (a) and without (baseline) GI measures (b). The value for indicator 1, “I₁” is:

$${\mathrm{I}}_1\left(\%\right)={\displaystyle \frac{\left(\mathrm{a}-\mathrm{b}\right)}{\mathrm{a}}}\times 100$$

(4)

Those indicator percentage differences between the baseline and after GI implementation can be categorized into five grades as displayed in

Table 5. GI grades for percentage indicator range.

Indicator Percentage Difference	GI Grade
<20	Very poor
40–20	Poor
60–40	Good
80–60	Very Good
>80	Excellent

.

During the life cycle of GIs, a monitoring system should be planned and implemented to measure physical, chemical and biological indicators such as water levels, water velocities, rain gauge, temperature, evaporation, soil moisture, turbidity, conductivity, infiltration, pH, and dissolved O₂. These results are essential to provide a better understanding of the functioning of GIs and improve their performance.

In addition to social, technical, policies and regulations analysis to identify the best GI alternatives, economic studies should be undertaken. They are crucial to carry out a methodical appraisal of GI projects.

One of the biggest barriers to the uptake of GI projects is the lack of financial resources and the knowledge about cost–benefit [108]. Another drawback is the insufficient information on operation and maintenance costs because these monetary values depend on the local conditions, life cycle, magnitude and kind of hazard, and it is most common to only find construction costs [109]. Moreover, the cost of GI implementation is the sum of the costs of purchasing property, design, maintenance, and salaries of administrative and technical personnel [110]. Furthermore, it is necessary to improve the understanding and development of exposure, and vulnerability research, with natural hazards, giving the risk assessment [101].

Life-cycle costing (LCC), cost–benefit analysis (CBA), cost-effectiveness analysis (CEA), eco-efficiency (EE), and input–output, are the main economic models used to assess water systems [111]. LCC considers all costs involved in implementation, operation, maintenance and monitoring, and end-of-life costs, and it is the most economical assessment used for GI projects. The difference between CBA and CEA is that CBA relates cost and benefit considering monetary terms during the lifetime, whereas CEA is applied when benefits (social or environmental) are difficult or do not have monetary value [108]. Therefore, the main purpose of CEA is to find the minimization of the implementation GI costs and the maximization of their benefit costs (effects of GI) [112].

The implementation and outcome (environmental benefit) costs are not constant over time [113]. In paper [112], it is stated that the CEA metric for a single benefit scenario I (with GI) is the relation between the cost of net present value NC_i and the cost effect E_i.

$${\mathrm{CEA}}_{\mathrm{i}}={\displaystyle \frac{{\mathrm{NC}}_{\mathrm{i}}}{{\mathrm{E}}_{\mathrm{i}}}}$$

(5)

$${\mathrm{E}}_{\mathrm{i}}={\displaystyle \sum }_{\mathrm{t}=1}^{\mathrm{Ti}}{\displaystyle \frac{{\mathrm{e}}_{\mathrm{i}}\left(\mathrm{t}\right)-{\mathrm{e}}_{\mathrm{o}}\left(\mathrm{t}\right)}{{\left(1+\mathsf{\rho }\right)}^{\mathrm{t}}}}$$

(6)

$${\mathrm{NC}}_{\mathrm{i}}={\displaystyle \sum }_{\mathrm{t}=1}^{\mathrm{Ti}}{\displaystyle \frac{-{\mathrm{c}}_{\mathrm{i}}\left(\mathrm{t}\right)+{\mathrm{b}}_{\mathrm{i}}\left(\mathrm{t}\right)}{{\left(1+\mathrm{r}\right)}^{\mathrm{t}}}}$$

(7)

where CEA_i = cost effectiveness analysis for a scenario i; NC_i = the present value of the net cost (EUR); E_i = the effect cost (EUR); T_i = lifespan (years); e_i and e_o: = outcomes for scenario i and baseline, respectively; at each time t; ρ = the social discount rate (%); c_i = the annual cost for scenario i (EUR); b_i = the benefits costs for scenario i (EUR); and r = the discount rate (%).

Meanwhile, to analyze CBA for various outcomes, it is necessary to select and evaluate multiple indicators to apply multi-criteria models. It is understood that every investment project needs to make a cost–benefit analysis (CBA), to appraise it [114]. The decision makers need a tool and results to compare different alternatives of the GI costs and the corresponding benefit costs for multiple service ecosystems [115].

The total cost of every GI considers the investment cost plus maintenance cost during the lifetime. Meanwhile, the effect is the benefit—for instance, for a retention pond, this could be the volume retained. It has been proved that natural solutions that function as mitigation structures could be two or five times more cost-effective than hard-engineered infrastructures [116].

Approvals, investments and decisions by managers, local or national authorities or policy makers require, in addition to the economic evaluation, measuring and recording certain variables embedded in the impact indicators (monitoring process) [117]. The monitoring activities are executed during the lifespan of GI projects.

3. Findings and Discussion

Green Infrastructure (GI) is considered some environmental resources such as forests, rivers, lakes, wetlands aquifers, soils, and landscapes which sustain our lives [37]. Furthermore, according to [118], a GI is any engineered infrastructure that employs natural materials, such as vegetation, soil and water. GIs offer benefits not only for water management but also multiple benefits. For instance, this improves urban microclimate and environment, air quality, and biodiversity, reduces urban heat islands, health benefits, carbon sequestration, green jobs opportunities, and increases real state [119].

On the other hand, there are barriers and strategies to developing a GI project that reference [120] discusses. They are financial restrictions, professional expertise, and legal frameworks. However, GI measures are not favorable for all conditions. The targets to be solved should be identified—for example, flood risk (quantity), pollution (quality), and co-benefits. Thus, it might be optimal to apply an integrated solution, which means some GIs must operate together [26].

The process of implementing nature-based solutions (NBS) or Green Infrastructure (GI) for urban resilience is a complex task, and there are several obstacles to tackle [121].

Despite the multiple benefits that GIs can afford, their intervention is quite slow, especially in developing countries [122], and the reasons are:

• Lack of understanding of performance, benefits, economic value, and awareness of GIs among decision makers who are in charge of approving projects of urban planning [123];
• Scarce knowledge of GI operation and maintenance procedures [124].
• Deficient or absence of policies, guidelines, legal framework, and regulations, that could provide the strategy to design, and implement NBS [37]. The success of these policies is when municipal authorities work together with community leaders, stakeholders, and environmental groups [125].
• Resistance from local municipality authorities, residents or stakeholders, owing to insufficient evidence of GI costs, monitoring, and maintenance of GIs. Hence, [126] has demonstrated the effective success of integrating multiple drivers into the project.
• There are cognitive and socio-institutional barriers. The survey [127] was conducted in ten US cities and found five types of barriers: federal and state barriers, city policies, governance, resource, and cognitive barriers. If the society has better knowledge of GIs, training and experts, the results will likely be reflected in a better and broader implementation of green and blue solutions.
• Inadequate GI planning. It must be part of the strategic spatial plan of cities, encompassing the following principles: connectivity, multifunctionality, diversity of green objects, multiscale, identity, landscape and water management [128]. The study in [129] analyzed 14 strategic plans belonging to 11 European countries, where at least half of them consider these principles; meanwhile, others have different interpretations.
• Weak urban planning. In [1], a framework was presented to strengthen urban planning by employing NBS, based on five trade-offs. They are temporal, spatial, functional, social equity, and species. One approach used may affect other approaches, services or benefits.
• Unsatisfactory land use planning. Lack of political will and insufficient monetary resources. GIS and remote sensing analysis would contribute to generating effective land use plans [130].

The authors of [131] mention that to be successful in the design, selection and implementation of GI measures, several aspects should be analyzed. First, morphology, geology, geotechnics, type of soils, land use, local needs, policies and regulations of the study area are required. Second, some indicators have to be delineated to evaluate the performance of GI solutions. For example, water quality, groundwater recharge, biodiversity, temperature diminishing, amenities, health, and real estate value, are within the principles. Third, according to [132], interdisciplinary participation and coordination must involve decision makers or city governments, stakeholders, community planners and dwellers, who have better knowledge to address problems to maximize the outcomes of GIs.

Furthermore, sociotechnical systems theory is required to develop GIs, that is the interactions between science, technology, economics, ecology and political issues. The authors of [133] developed a policy procedural framework. This study is based on four stages: policy creation, construction management, evaluation operation, and reporting on best management practices, which were applied in a green infrastructure experiment in 27 cities in the United States.

Another challenge to implementing, selecting and investing in GIs is conducting an economic assessment of GIs. This assessment involves quantifying the economic value and benefits of green infrastructure, i.e., cost–benefits analysis of improved air and water quality, reduced flood risk, esthetic values, etc. [134].

Several works prove evidence of GI benefits. The results obtained in [135], show a 56% reduction in flood damage in Barcelona by employing green roofs, bioretention cells, and detention and retention ponds. Meanwhile, they found a 24% reduction in esthetic and habitat provision benefits in Badalona, Spain after the implementation of green roofs, infiltration trenches and permeable pavements.

In Nanjing, China, individual and combined GI scenarios were evaluated to reduce surface runoff volume [136]. The most individually profitable GI was grassed swales, and green roofs were the least valuable. The best combination of GIs in this study area was rain cisterns and permeable pavements. Another study was developed in a watershed (27 km²) in Michigan, USA [137]. Its goal was to evaluate the performance and cost–benefit of GIs in stormwater management, through the use of hydraulic simulations. The findings mentioned that grass swales, rain barrels and dry ponds were the most cost-effective and the green roof was the most expensive.

Furthermore, ref. [138] found multiple benefits of grasslands, and trees, for water management indicators. Water storage was from 20% to 100%; surface runoff was reduced by 68% and 100% for rainfall return periods of 10 and 2 years, respectively, whereas ref. [139] demonstrates the improvement of water quality by reducing the concentration of pollutants (zinc, glyphosate, pyrene and phenanthrene) from 65% to 100% through infiltration into swales.

In this research, 351 documents were obtained in the filtering process by criteria in phase one, divided into 264 papers, 15 guidelines, 28 journals, 34 reports handbook, and 10 doctoral thesis. This review process was focused on the last five to six years of publication. These documents were classified under different criteria, which are used to identify and define indicators to assess the performance of GIs. Figure 7 depicts the number of articles selected by each criterion.

According to several guidelines for evaluating nature-based-solutions impacts [68], performance indicators are required to assess these natural solutions [78]. Although these guidelines presented a huge number of indicators, in the present research, only the most relevant and impactful indicators were identified. In this context, several aspects were examined to define the indicators across the defined criterion.

• Urban drainage management: watersheds provide some ecosystem services that benefit society; however, the increase in impervious surfaces has led to several impacts on the hydrological cycle [140]. Hence, to protect the community from negative effects such as pollution and flood, hygiene, engineering or hard infrastructures have been developed. Nevertheless, these are not sustainable solutions. GIs provide another philosophy to address those adverse effects [141]. They ameliorate surface runoff, peak flow, nitrogen and phosphorus concentration, and increase infiltration. Under this criterion, the “dry weather runoff”, “stormwater management”, “stormwater retention within the climatic group”, and “reduced peak discharge” indicators were of a total of twenty-five documents. The research of [142] indicates that hybrid solutions reduce 23% of flooding and the GI decreases by 20%, whereas 20% of heatwaves are managed by GIs.
• Urbanization is one of the most pressing issues that provokes adverse impacts on the water resources [143] and promotes water scarcity, water demand increment, domestic and industrial pollution, and flood hazard [144]. Hence, implementing GIs is arguably necessary to reduce stormwater runoff and mitigate flood hazard [54]. Four articles were selected out of seventeen with four indicators: “urbanization dynamics”, “relationships of comprehensive urbanization index—drainage system health CUI-DHI”, “reduction of runoff coefficient”, which has incidence in the urban drainage design, and “increase imperviousness ratio”.
• Climate change is incrementing the probability of occurrence, duration and magnitude of hazards, exacerbating environmental, social, and economic consequences and even loss of human lives. Green infrastructures can contribute to society coping and recovering from disasters [18]. Both urbanization and climate change are the main challenges to be faced, where greater rainfall events and dry periods have increased markedly [38]. These challenges could be addressed by applying sustainable solutions to reduce thermal conditions, urban heat islands [145], improvement of microclimate and air quality, human comfort, and energy saving through air cooling [146]. Other research proposed several key performance indicators (KPIs) about Sustainable Development Goals (SDGs) and ecosystem services (ES), which are crucial to maximizing GI behavior [147].
• Urban regeneration refers to the entire process of transition from degraded urban areas with poor environmental quality of life to the community turned into livable, tourist, attractive and productive zones, through natural blue–green measures [75]. GI solutions can contribute multiple benefits: fostering the local economy, creating attractive and safe public spaces, opportunities to citizens for new business, increasing property values, and recovering and protecting the urban environment [148].
• Co-benefits: in addition to flood hazard reduction, there are other positive outcomes to apply GIs, called co-benefits [149]. GIs contribute to restoring ecosystem services, which contain environmental and socioeconomic issues [131]. Examples of these are physical, health, and psychological [123]; educational aspects: ecosystem restoration and increased biodiversity [150];improved water and air quality [151]; carbon reduction and sequestration, recreational activities, urban cooling, noise pollution reduction, water retention, water demand reduction [152].
• Social–stakeholder participation: inclusive participation of a variety of stakeholders, groups such as practitioners, commercial sector, academia, municipal technicians [153], experts, citizens, and non-governmental organizations, should be involved in the co-creation of GIs [154]. The participation and engagement of these interest groups are fundamental to increasing the level of acceptance, effectiveness, and sustainability in GI planning and designing [155]. Two indicators were selected in this criterion: “resident accessibility of GI” and “co-design by a group of interest”;
• Policy regulation: governments and municipal authorities must promote policies, regulations, standards, and guidelines, that provide support to plan, design, implement, monitor and maintain GIs [156]. Due to a lack of political support, regulation and guidelines, GI projects will be ignored and not implemented [157]. Stakeholders, academia, local authorities, and citizens play an important role in reviewing, improving and developing regulations and policies to overcome constrains to implement GIs [158]. There are some regulations as [159], which was published by the municipality of Quito, Ecuador, which considers the implementation of blue–green infrastructures in urban planning. However, it is not enough—it is necessary to develop design guidelines according to the reality of the area, with the participation of stakeholders, citizens and academia.
• Modeling performance: to analyze hydro-meteorological risk scenarios under projected climatic change, it is necessary to develop tools such as a hydrodynamic model to understand the dynamics of surface runoff within the basins and in urban drainage [42]. Therefore, to mitigate this natural threat, GIs could be applied; nevertheless, its optimal design, location and performance can be known by using numerical modeling [160].
• Urban resilience: cities face complex challenges, related to social, environmental, and economic aspects, which have been rising over recent decades [161]. Associated with them are climatic change, population growth, urbanization, and the advent of industrialization and technology [5]. To enhance urban resilience, diminishing disaster risk and nonpoint source contamination in urban water bodies, sustainable strategies are required to achieve social and environment benefits and human well-being [162].
• Economical assessment: Aside from the technical, social, environmental, and legal issues of GIs, cost–benefit analysis is crucial as well [135]. The economic assessment must be carried out, analyzing investment and benefit costs. The outcomes include not only flood damage reduction but also the co-benefits [163]. Although the biggest impact on the economy is due to natural hazards, only 1% of funding goes to disaster risk management [164,165].
• Monitoring and maintenance: collecting data from GI maintenance and monitoring activities is beneficial for making better future decisions for optimal and appropriate design and implementation of these sustainable solutions [166]. Maintenance refers to the actions that include schedule activities of vegetation management, modification and replacement of silt, and oil, sediment cleaning up, and litter and debris removal [167]. Monitoring is the measurement of quantity and quality variables in GIs, such as flow rate, water level, total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) [168].

It is globally acknowledged that blue–green natural solutions are capable of addressing global socio-environmental pressures and their adverse effects. However, evaluation of the effectiveness of GIs can be performed by using indicators, which ought to be appropriate to assess the performance and impact of these solutions [169].

According to some guidelines [170], there are indicators classified as structural, process and outcome. These indicators can be employed before, during and after the implementation of GIs.

Through the analysis of several studies collected in the first phase, the most valuable indicators were identified under each criterion and some of them are measurable and others are not.

Table 6. Indicators related to defined criterion.

Criteria Urban Drainage Management
Indicator	GI/Tool	Outcomes	Country	Source
Dry weather runoff	BR + IT	Prototype GI + UD + social	Costa Rica	[171]
Stormwater management	RG + GR	Improve ecosystem services	USA	[133]
Stormwater retention with climatic group	GR	A:34%; B: 25%; C: 31%; D: 32%%	Canada	[172]
Reduced peak discharge	EMPs	52%	Costa Rica	[173]
Criteria Urbanization
Urbanization dynamics	[Google Earth, DMSDP/OLS	Spatial patterns in cities	Bolivia, Ecuador,	[174]
	[FUAs]	Spatial patterns in cities	Colombia Perú	[175]
CUI—DHI	Modeling	Curve relationship CIU-DHI	China	[143]
RC reduced	Modeling	RC–cost relationship curves	Saudi Arabia	[12]
Increase imperviousness ratio	Modeling	Increase flooding volume by 38%, and flooded nodes by 67%	Ethiopia	[176]
Criteria Climate Change
Indicator	GI/Tool	Outcomes	Country	Source
Urban heat island	GW, GR	Save energy and noise pollution, reduction temperature	Austria	[38]
Thermal comfort	GR, PP, BR, RG	RG and trees are the best	Thailand	[177]
Surface, air temperature	SV; T; UP; GW; GR	[1–3.5; 3–16; 1–6; 7–17; 10–17] °C	Switzerland	[178]
Criteria Urban Regeneration
Social health environmental benefits	UA	Improve food access and production, neighborhood and build community capacity	USA, Hungary	[179]
	RC	Re-planning area		[180]
Fertile soil	NS	Industrial regeneration by reusing building material	Italy	[181]
Urban tree ecology	PW, SS, T	Reduce uncertainty performance urban tree	Canada	[182]
Hydro-meteorological risk reduction	RT, F; SST	Regeneration Tourist Park in the Mediterranean Region	Italy	[183]
Criteria Co-Benefits
Economic, social, environmental	[GR + BR + RG + PP + IT + RB]	Framework to select GI	Thailand	[131]
Ecological benefits	PP + GR + BR	Ecosystems services, ecological status, ecological connectivity, proximity to human populations	UK	[123]
	PP + GR + BR	Ecosystem benefits	UK	[149]
	GI surveys	Human perception	China	[184]
Water retention, and reduction in potable water	BR	31.2 mm/day	Canada	[185]
	SWH	30%	New Zealand	[186]
Criteria Social Participation
Resident accessibility of GI	GS	Green accessibility index	China	[187]
Co-design	GI prototype	Framework transdisciplinary participation	Costa Rica	[47]
Criteria Policy Regulation
Barriers to implementing GI	Policy Feedback Cycle	Policy Guidelines	Costa Rica	[125]
	GI Ordinances	Cognitive and Socio-Institutional barriers	USA	[127]
	Legal Planning	Strategic Plans	Switzerland	[129]
	Policy Feedback Cycle	Sociotechnical Framework	USA	[133]
Criteria Modeling Performance
Indicator	GI/Tool	Outcomes	Country	Source
Total annual runoff reduction	RG, RB []	[10–32%]	USA	[188]
	RC + PP	2–12%	USA	[189]
	RC + BR + PP	23.5%	USA	[190]
	GR + BR + PP	35–42%	Hong Kong	[191]
	BR + IT + S + PP	22–24%	Colombia	[192]
	PP + IT + DW + GR + RG	101%	Korea	[193]
Pollutant load reduction TSS-TN	RC + BR + PP	30.8–27.9%	USA	[190]
	BR + IT + S + PP	12–15%	Colombia	[192]
	PP + IT + DW + GR + RG	113%	Korea	[193]
Spatial planning	Web Gis	GI planning	USA	[25]
	BR + PP + GR	GI design plannig	UK	[52]
	Frameworl Planning	GI Planning	Ghana	[194]
	GIS	Landslide reduction	Italy	[195]
Land value increase	FP, DB	4.2%	Brazil	[196]
Criteria Urban Resilience
Urban planning	Trade-offs: spatial, functional and social equity [Geospatial analyses]	Framework to guide implementation GI	Australia	[1]
	Geo-spatial analyses	Baseline Land Use Planning	Nigeria	[130]
Criteria Economical Assessment
Cost–benefit analysis		Effectiveness 20–70%	Italy	[110]
	GR, BR, DB, PP, IT	Cost: 80 EUR/m2, 45 EUR/m2, 100 EUR/m2, 49.5 EUR/m2, 185 EUR/m2. Benefit: Flood damage reduction 56%, water quality 24%, additional 20%	Spain	[135]
Criteria Monitoring Maintenance
Surface runoff reduction	T; RP, P	25–30%	UK	[126]
	GR, S, BR	52, 80, 63%	Spain	[166]
Infiltration efficiency	PP, GA	KPP ˃ 10 KGA	UK	[197]

outlines these performance indicators.

This article provides an overview of scientific documents, highlighting the growing global interest in innovative and profitable approaches based on natural and sustainable solutions, as a measure to adapt and counteract the adverse effects of urban dynamics [161]. These studies have demonstrated the role that a GI plays in enhancing ecosystem services, socio-ecological and economic benefits, and reducing disaster risks [198].

The range of GI interventions is wide and depends on many factors, as explained above. They can be implemented alone or by combining some of them [199]. Their evaluation and monitoring is not a simple task [200]. The authors of [73] remark that the selection of adequate criteria and indicators is vital to maximize the performance of these sustainable structures.

Although some guidelines identified a significant number of indicators, it is unlikely that all of them will be applied to evaluate GI performance. This depends on the challenge to be solved, the local priorities, and the needs of the end-users.

The authors of [117] selected 262 articles for their research, where 33.2% are related to hydro-meteorological hazards. Within them, 9.9% correspond to floods, and in South America, only 1.3% of papers on nature-based solutions have been developed.

In this sense, this research has focused on proposing a framework to address Hydro-meteorological hazards considering social benefit and the availability of policies and regulations as well. In this framework, different alternatives of GIs or hybrid infrastructures should be analyzed. And their effectiveness has to be evaluated by applying the most appropriate indicators, to improve urban resilience. The effectiveness of natural solutions compared to grey infrastructures was described by [201], where flood volume and surface runoff were reduced by approximately 15–40% more when SUDs were implemented.

According to the need and local conditions and peculiarities of the study area, basic data should be collected, analyzed or generated to evaluate the effectiveness of integrated hybrid solutions. It will be necessary to collect relevant, accurate and multiple input data, among the principles are: hydrological, land use, soil and geologic data, digital elevation model (DEM), wastewater flows, watershed and drains characteristics, topological information of sewer system, socioeconomic, and demographic.

This information is required to build a hydrodynamic model to simulate the hydrologic–hydraulic of the major system (overland flow) and the minor system (sewer network). This tool of the numerical model is quite important to understand the current performance of the area (baseline) and to predict future scenarios of land use change, population growth, and rainfall regime, due to climate change and urbanization.

Based on simulation results, designers, planners or practitioners could select critical zones of the study area, where it will be necessary to develop alternatives with the optimal combination of GIs with grey infrastructures with the best location. Afterwards, the solutions adopted must be implemented in the model to generate results with and without GIs.

The performance of the selected mitigation actions can be evaluated by using some indicators. This will be adopted by taking into account issues related to flood risk, urban regeneration and resilience, human well-being, and biodiversity, considering policies, regulations and guidelines aspects [202]. These indicators must reproduce useful and relevant information to support decision makers and obtain financial resources, whose results must be understandable to non-experts, citizens, and stakeholders.

To monitor the performance of GI solutions, laboratory experiments, surveys, and direct measurements must be performed by using automatic sensors. Results of different variables are obtained to contrast them with simulation results from modeling approaches [69]. However, there are qualitative observations, which can be obtained with other methods such as surveys and census, especially the information related to human behavior of acceptance of GIs.

Following a comprehensive analysis of the indicator dataset, the most pertinent and robust metrics for evaluating and monitoring Green Infrastructure (GI) in the context of hydro-meteorological hazard management are shown in

Table 7. Proposed indicators for hydro-meteorological hazards.

Indicator	Unit	Tools	Source
Peak flood reduction	%	Hydrologic and Hydraulic Modeling	[203]
Nodes flooded	No.	Hydrologic and Hydraulic Modeling	[69]
Flood volume reduction	m3	Hydrologic and Hydraulic Modeling	[204]
Flooded area	ha	Hydrologic and Hydraulic Modeling	[203]
Increase time to peak flow	min	Hydrologic and Hydraulic Modeling	[203]
Surface runoff reduction	%	Hydrologic and Hydraulic Modeling	[204]
Social—Health Well-Being
Urban heat island reduction	°C	Measurements	[205]
Air quality	Concentration particle matter	Measurements	[206]
Recreational green areas and management	ha	Geographic Information System	[207]
Stress and anxiety reduction	No. people	Surveys	[208]
Recreation–esthetic values	Interviews	Surveys	[204]
Community Involvement
Citizens and stakeholders involved	Interviews	Surveys	[209]
Economical Assessment
GI cost–benefit analysis	USD	Hydrologic and Hydraulic Modeling	[210]

. These indicators are those that demonstrate optimal performance in attenuating surface runoff impacts, mitigating flood risk, and addressing socio-environmental vulnerabilities, all while achieving favorable cost–benefit ratios.

The authors of [142] proposed a summary of the study results, demonstrating the effectiveness of GI interventions in managing hydro-meteorological hazards (

Table 8. Indicator efficiency range for different risk events.

Risk Events	GI Type	Indicator Efficiency	Source
Floods	Green roof	45–70%	[211]
	Small ponds	18–20%	[120]
	Rain garden	62–98%	[212]
Storm surges	Coast wetlands	20–30%	[165]
	Coral reefs	54–81%	[165]
Heatwaves	Urban parks/trees	2.0–3.5 °C	[213]
	Forest	5–30 °C	[213]

).

Among the natural solutions to face the threats of Hydro-meteorological hazards, are: flood plains, retention, detention ponds, rain gardens, bioretention, permeable pavements, green roofs, swales, infiltration trenches, street trees, parks, and urban forests [204]. Severe rainfall events can be transformed into 95% of surface runoff in sealed areas, which can be reduced by 14.8% by implementing green roofs, and trees [138].

Table 9. Effectiveness indicators for different GIs [70].

Effectiveness Indicators	GI Type	Percentage Values Obtained
Runoff volume reduction	Porous pavement; green roofs; rain gardens; swales; rainwater harvesting; detention ponds; bioretention; infiltration trenches	30–65; 70; 100; 10; 57–79; 56; 90; 56
Peak flow reduction	Porous pavement; green roofs; rain gardens; swales; rainwater harvesting; detention ponds; bioretention; infiltration trenches	10–30; 96; 49; 24; 46; 42; 54

shows the more effectiveness indicators according to [70], which are considered for some GI interventions to address flood risk reduction.

Successful implementation of GI solutions requires additional aspects mentioned before—availability of public space in urban areas; analysis of pollutants from surface runoff to prevent groundwater contamination; transboundary catchment with different regulatory actions [214], type of vegetation that resists periods of drought and root damage on roofs [215].

The determination of indicator thresholds depends on the characteristics of the region, the problem that has to be solved by GIs, and the magnitude of the project from small to large scale as well [79]. The effectiveness of natural solutions can fluctuate over time. Many factors include the dynamics of social–ecological systems, changes in authorities and decision makers, inflation, and severe hydrological events. Finally, a procedure must be defined to score the indicators to generate a decision matrix to choose the best scenario based on the weighting of the indicators [216].

After examining all the articles, with different procedures and frameworks to assess the efficiency of GIs, it can be concluded that the projects developed in, such as UNaLab, PHUSICOS, and RECONNECT, are the most complete studies, which can give great support to and guide developing countries.

4. Conclusions

Throughout history, humans have sought to control and exploit nature’s resources for their convenience, aside from growing populations and unplanned urbanization exacerbating social, economic and environmental crises. Hydro-meteorological risks are the most devastating natural hazard for human; however, little attention has been paid to risk research in mountainous cities, where these hazards are significantly amplified.

In this context, this study presents a comprehensive framework to evaluate the effectiveness of Green Infrastructure (GI) in mitigating the impacts of Hydro-meteorological hazards and enhancing urban resilience. While extensive research underscores GI’s role in providing sustainable benefits, such as restoring ecosystem services (benefits that society receives from nature), reducing risks, and improving urban livability, urban and natural ecosystems remain under significant strain from urbanization, population growth, and climate change. These pressures exacerbate challenges such as increased flood risks, property damage, disruptions to utilities, public health issues, and environmental degradation.

This framework is structured in three phases: in the first phase, a systematic literature review was carried out to retrieve and classify publications under twelve criteria. In the second phase, methods, tools and the most relevant indicators were identified from those scientific articles. Meanwhile, in the third phase, the framework involved several steps, which are interconnected with each other. The initial conditions (baseline) are evaluated by applying hydrologic–hydraulic modeling. Groups of stakeholders considering local conditions and needs, pressures that will be addressed, geology and geotechnical characteristics, and availability of policies should select and co-design the most appropriate GI and indicators. The results of the effectiveness of the GI project take into account both the analysis performance of indicators and the economical assessment.

The proposed indicators measure GI performance across multiple dimensions, focusing on key metrics such as reductions in flood peaks, flood volumes, flooded areas, and surface runoff. These metrics are crucial for quantifying GI’s capacity to mitigate hydro-meteorological hazards. Furthermore, the framework extends beyond risk reduction by incorporating indicators for broader social and environmental benefits, including urban heat island mitigation, improved air quality, expanded recreational green spaces, and enhanced community well-being through stress reduction and mental health improvements. This holistic perspective highlights GI’s multifunctional potential, addressing both disaster resilience and the improvement of urban quality of life.

Future research should prioritize the refinement and validation of these indicators through real-world applications and case studies, particularly in diverse urban settings and regions highly susceptible to climate impacts, such as South America. Emerging technologies in remote sensing, numerical modeling, and data analytics offer promising opportunities to enhance the accuracy and scalability of these indicators, enabling more robust and evidence-based GI planning. By introducing this integrative framework, this study provides a novel strategic tool for decision makers, emphasizing GI’s scalability and its pivotal role in designing resilient and sustainable cities.