Hydrosphere Under the Driving of Human Activity and Climate Change: Status, Evolution, and Strategies

1. The Critical Role of the Hydrosphere in the Earth’s System

The hydrosphere is a foundational component of the Earth’s systems, sustaining biological processes, regulating environmental stability, and enabling socioeconomic development [1,2]. As the primary medium for biogeochemical cycles, it governs global energy distribution, nutrient transport, and habitat provision for both aquatic and terrestrial ecosystems [3]. While 71% of the Earth’s surface is covered by water, accessible freshwater resources constitute less than 1% of total reserves [4], highlighting its irreplaceable value in supporting agriculture, industry, and domestic needs. Historically, human civilizations have thrived along river valleys and coastal zones, relying on water for irrigation, transportation, and cultural practices [5]. The development of groundwater abstraction techniques has facilitated the establishment of human settlements and socio-economic activities in regions historically constrained by the availability of surface water resources. Beyond its water supply functions, the hydrosphere modulates climate patterns through ocean–atmosphere interactions and acts as a critical buffer against temperature extremes [6]. Its intrinsic linkages to the atmosphere, lithosphere, and biosphere underscore its centrality in maintaining planetary equilibrium [7], making its preservation imperative for ecological integrity and human survival.

2. Emerging Threats to Hydrospheric Stability

Anthropogenic activities and climatic disruptions have accelerated the systemic degradation of water resources, marked by both quantitative depletion and qualitative deterioration [8,9,10]. Overexploitation of groundwater resources, driven by agricultural intensification and urbanization, has led to aquifer depletion rates that exceed natural recharge capacities in many regions worldwide such as China, Chile, India, Mexico, and Iran [11,12,13,14,15]. Concurrently, industrial effluents, agricultural runoff, and plastic pollution have compromised water quality, posing threats to aquatic biodiversity and human health [16,17,18,19,20]. Climate change exacerbates these challenges by altering precipitation regimes, accelerating glacial melt, and amplifying extreme hydrological events, including floods and droughts [21]. Projections indicate a potential 40% global water deficit by 2030 under current consumption trends [22], with transboundary water conflicts intensifying geopolitical tensions. Additionally, rising sea levels [23] and ocean acidification [24] jeopardize coastal ecosystems, further compromising food security and disaster resilience. These cascading impacts underscore the urgency of addressing hydrospheric vulnerabilities within integrated sustainability frameworks.

3. Knowledge Gaps in Hydrospheric Research

Despite significant progress in hydrological sciences, critical knowledge gaps persist in understanding how the hydrosphere responds to combined stressors of rapid and drastic human-induced climatic changes. Previous studies have inadequately represented feedback mechanisms between anthropogenic water use, climate variability, and ecosystem dynamics, particularly across various scales from inland to coastal regions. Limited long-term monitoring of data hinders the assessment of water resource depletion trends and contaminant dispersion pathways, especially in developing countries with fragmented hydrological networks. Additionally, socio-hydrological interactions, such as the interplay between water governance, economic policies, and community adaptation, remain under-researched, hampering the design of context-specific mitigation strategies. The integration of emerging technologies with traditional methodologies is still in its infancy, limiting the accuracy of predictions for extreme hydrosphere events. Future research must prioritize interdisciplinary approaches, improve the spatiotemporal resolution of datasets, and incorporate indigenous knowledge systems to address these limitations and inform resilient water management paradigms.

4. Papers in This Topic

A total of seven journals, including Atmosphere, Land, Remote Sensing, Sustainability, Water, Earth, and Hydrology, participated in this Topic. Numerous manuscripts were submitted to these journals, and ultimately, 17 manuscripts passed the rigorous peer-review process and were accepted for publication by four journals including Land, Sustainability, Water, and Hydrology (as shown in the list of contributions).

The studies cover a range of environments from continental interiors to transitional coastal zones, systematically examining hydrological compartments across both surface water systems and subsurface groundwater reservoirs. Multiple contributions focused on characterizing groundwater systems in arid regions, particularly on how hydrogeochemical processes fundamentally govern long-term resource sustainability under persistent water scarcity. Current investigations systematically examine the complex interplay between geochemical evolution pathways and hydrological constraints that shape water accessibility patterns in moisture-deficient environments [25,26,27,28]. Meanwhile, some studies assessed hydrochemical dynamics within terrestrial-marine ecotones, particularly in coastal transition zones experiencing saline intrusion and synergistic anthropogenic pressures [29,30,31]. Human-induced organic contaminants in groundwater systems were investigated using approaches such as hydrochemistry, isotopes, microbial techniques, and numerical modeling to assess their distribution, migration, natural attenuation, and threats [32,33]. Geochemically distinct groundwater resources, notably mineral-enriched aquifers, were systematically investigated for their spatial heterogeneity and hydrogeological formation mechanisms, with particular emphasis on their roles in potable supply and therapeutic applications [34]. Additionally, the geochemical signatures, evolution, and formation of deeply buried continental brines have been explored, providing a valuable hydrogeological “window” into these liquid resources enriched in rare metal minerals [35].

The interconnectedness of water systems and ecosystems under anthropogenic perturbations was explored, with a particular focus on how human-induced surface and subsurface hydraulic modifications mediate hydro-ecological feedback mechanisms. River runoff dynamics in semiarid basins have been examined, revealing that anthropogenic activities are the predominant factors leading to runoff reduction [36]. Additionally, the hydrological connectivity between coastal terrestrial ecosystems (e.g., wetlands) and adjacent marine aquifers has been extensively investigated, with particular emphasis on their bidirectional interactions with human activities in coastal zones [37,38]. These studies reveal significant anthropogenic modifications to hydrological exchange processes that fundamentally alter both ecological integrity and geological stability within these transitional environments. Contemporary research increasingly documents how human-induced perturbations disrupt natural biogeochemical cycles while exacerbating geological vulnerabilities in coastal interface systems. Furthermore, the hydrological impacts of land-use change in semiarid inland basins have been explored from the Production–Living–Ecological Space perspective [39]. Results indicate that the spatiotemporal configuration of territorial functions (production, living, and ecological) fundamentally regulates watershed hydrodynamics. Specifically, the reduction in ecological zones is quantitatively correlated with decreased aquifer recharge efficiency and compromised moisture retention capacities in semiarid terrestrial systems. Comprehensive analyses of soil moisture retention attributes reveal that textural composition exerts dominant control over unsaturated hydraulic property relationships, with distinct soil textural patterns governing pore-water retention behavior in variably saturated subsurface systems [40]. Anthropogenic infrastructure development, particularly traffic tunnel construction, has also been systematically investigated and evaluated for its potential to trigger perturbations in groundwater systems and natural hydrogeological landscapes [41].

5. Final Remarks

This collection significantly advances our understanding of hydrological systems across continental to coastal environments, with a focus on hydrogeochemical processes, human impacts, and resource sustainability. Key findings reveal how groundwater evolution in arid regions is governed by geochemical–hydrological interactions under water scarcity, while coastal zones face compounded threats from saline intrusion, contaminants, and anthropogenic pressures. Multidisciplinary approaches—integrating isotopes, microbial analyses, and modeling—prove vital for tracking contaminant dynamics and natural attenuation.

The studies underscore the profound anthropogenic role in reshaping hydrological-ecological connectivity. Semiarid regions exhibit reduced runoff due to human activities, coastal ecosystems experience altered hydraulic feedback, and land-use shifts disrupt aquifer recharge and soil moisture retention. Infrastructure development, particularly tunnels, further highlights risks of groundwater system perturbations.

Future priorities include refining predictive models for multi-stress scenarios, unlocking insights from deep brines and mineralized aquifers, and mitigating anthropogenic disruptions through evidence-based safeguards. As environmental pressures intensify, fostering interdisciplinary collaboration and science-policy synergy remains critical to securing equitable, sustainable water futures. Collectively, these works chart a path for innovative research and actionable solutions to protect the Earth’s vital water resources.