Advances in Ecohydrology in Arid Inland River Basins

1. Introduction

Water is the foundation of life, ecosystems, and socioeconomic development [1]. Hydrological mechanisms, including flood and drought events, pollution, and water scarcity, underlie climate–soil–vegetation dynamics and control the most basic ecological patterns and processes, both for biota and materials [2]. Nowhere is this more evident than in arid and semi-arid regions, where the complex interplay between climate variability, human activities, and ecological systems shapes both the challenges and opportunities for sustainable water management [3,4,5,6]. Over the past few decades, rapid climatic shifts, intensified land use, and increasing anthropogenic pressures have exacerbated water scarcity, threatened ecological security, and heightened the need for innovative management strategies in these vulnerable landscapes.

The area of arid and semi-arid regions has expanded further with global climate warming, which has had profound impacts on the functional structure of ecosystems in these regions. This, in turn, has significantly affected humans’ ability to access water resources [7]. Moreover, human activities, such as the development of water infrastructure and changes in land use, have caused profound disturbances to the ecological hydrological processes in arid and semi-arid regions [8,9]. Therefore, the ecological hydrological mechanisms in arid inland river basins require further investigation [10,11].

This Special Issue of Water brings together twelve cutting-edge studies that advance our understanding of water resources, hydrological processes, ecological risk, and sustainable management practices in arid and semi-arid environments. Collectively, these contributions offer novel insights into soil infiltration, hydrological modeling, drought assessment, water quality, vegetation dynamics, landscape ecological risk, water governance, and adaptive management strategies under the influence of both natural and human-induced changes.

This editorial aims to highlight emerging trends in the sustainable management of ecohydrological systems in arid regions. The studies in this Special Issue showcase interdisciplinary research approaches, provide diverse perspectives for uncovering the mechanisms of ecohydrology, and clarify how integrated scientific research can inform policy-making, support sustainable development in arid inland river basins, and enhance the resilience of ecosystems in arid inland river regions under the background of global climate change.

2. Review and Synthesis of Contributions

1. Soil Infiltration, Vegetation, and Land Cover Change

Soil infiltration is a key factor influencing surface runoff, groundwater recharge, and ecosystem functioning, particularly in regions where water resources are limited. The work in [Contribution 1] compares the soil infiltration capacity between native grasslands and thicketed oak woodlands across different soil types. Their findings indicate that converting oak savannahs to thicket-dominated woodlands can notably increase soil infiltration, especially in clay-rich soils. The study also evaluates several infiltration measurement methods and highlights the Simplified Steady Beerkan Infiltration (SSBI) technique as a rapid and practical alternative to traditional rainfall simulation for field assessments.

Changes in land use and land cover (LUCC) further shape hydrological processes and ecological risks. In the Kriya River Basin, the authors of [Contribution 9] use spatial modeling to show that both natural factors and human activities affect landscape ecological risk. The conversion of grasslands and unused land into croplands and built-up areas reflects the highly dynamic nature of land systems in arid regions. The research emphasizes that human activities have become the dominant force behind landscape risk and that different scenario-based projections—such as natural development, cropland protection, and ecological priority—lead to very distinct risk patterns. These results stress the importance of flexible land management and integrated risk assessment approaches to maintain ecological security in a changing environment.

2. Hydrological Modeling and Flood/Drought Risk

Hydrological processes in arid and semi-arid regions are often complex, with both episodic flooding and prolonged drought posing significant challenges for water resource management. The study of the Jingjiang–Dongting Lake system in [Contribution 2] highlights the intricate relationships between rivers, lakes, and flood control infrastructure. By building and validating a hydrological model with nearly 60 years of flood data, the research offers insights into the limitations of current flood mitigation strategies. Even with the operation of upstream infrastructure such as the Three Gorges Dam, it remains difficult to eliminate flood risks in the Dongting Lake area, suggesting the ongoing need for embankment reinforcement and policy innovation.

Concerns about drought are evident in the Manas River Basin [Contribution 5] and Huangshui River Basin [Contribution 3]. In the Manas River Basin, long-term analysis using the Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Runoff Index (SRI) shows that, while both meteorological and hydrological droughts have generally eased in recent decades, meteorological droughts during spring and autumn persist, and severe droughts are becoming more frequent. This highlights the need for scale-specific drought risk assessments and targeted management strategies. In the Huangshui River Basin, declining runoff and reduced ecological flow assurance since the early 1970s are closely related to intensified human activity. Still, ecological flows remain sufficient in most months, indicating the effectiveness of flow management but also the increasing vulnerability of river ecosystems to human pressures.

The authors of [Contribution 11] examine the impacts of water conservation projects and reservoir construction in the Weigan River estuary. Using a SWAT model integrated with glacier modules, the study quantifies how climate change, water engineering, and runoff have interacted over the past fifty years. The findings show that artificial regulation, particularly in spring, has significantly altered natural flow regimes, helping to ease seasonal shortages but requiring continuous evaluation to balance ecological and human needs.

3. Water Quality, Agricultural Practices, and Resource Allocation

Sustainable water management involves not only securing water quantity but also addressing water quality, especially in areas where agriculture, urban growth, and ecological conservation intersect. In south-central Ningxia, the authors of [Contribution 4] report that although water supply is generally adequate, water quality—specifically, persistently high total nitrogen—remains an issue. The study proposes and tests an optimized scheduling scheme, demonstrating that it is possible to improve water quality while meeting quantity demands, with reductions in total nitrogen exceeding 78%. These insights offer valuable guidance for other regions facing similar challenges.

Agricultural water use is closely tied to weed management and pesticide application, as discussed in [Contribution 10]. Limiting herbicide use in sensitive water zones can benefit aquatic biodiversity and environmental health but may also encourage the spread of particular weed species, complicating crop management. The research calls for innovative and integrated weed control approaches that balance agricultural productivity and water resource protection, underlining the need for cross-sectoral management.

Resource allocation is particularly complex in regions such as northwest China, where socioeconomic development depends on rational water distribution between urban and rural areas. These studies underscore the importance of considering both quantity and quality, optimizing allocation schedules, and involving local stakeholders to ensure sustainable outcomes.

4. Vegetation Dynamics and Ecological Restoration

Vegetation is central to ecosystem resilience, land–atmosphere interactions, and the provision of ecological services in drylands. The lower reaches of the Tarim River [Contribution 6] provide a telling example of vegetation recovery under changing climatic and human pressures. Using trend analysis, Hurst exponent projections, and GeoDetector modeling, the research documents significant improvements in the NDVI (Normalized Difference Vegetation Index) over the past twenty years, primarily driven by human intervention and proximity to river channels. However, the risk of future degradation persists, especially in areas far from water sources, as multiple factors combine to influence vegetation dynamics. These results are crucial for guiding targeted restoration and monitoring.

Research on the Great Lakes Depression [Contribution 12] further highlights the sensitivity of vegetation cover to hydro-climatic changes in Central Asia. In this region, rising temperatures, decreased precipitation, and lower river discharge have reduced lake water levels and altered vegetation patterns across diverse microenvironments. The study draws attention to the seasonal nature of vegetation responses to climate extremes and underscores the importance of integrated hydrometeorological and remote sensing analyses for monitoring and managing ecological change.

5. Climate Change, LUCC, and Streamflow Projections

Understanding how climate change and LUCC interact to affect hydrological processes is critical for future water security. The upper Tarim River [Contribution 7] is especially vulnerable, with projections suggesting that increased precipitation and temperature (under three socioeconomic scenarios) would raise streamflow, but ongoing LUCC—mainly the expansion of farmland at the expense of grasslands—would decrease it. Notably, LUCC is expected to have a greater impact on streamflow than climate change alone, with streamflow reductions projected under all future land use patterns. These findings reinforce the need for scenario-based integrated planning that accounts for multiple interacting drivers over time.

6. Water Governance and Socio-Institutional Innovation

Effective water governance is the foundation of sustainable management, particularly in regions that regularly experience both floods and droughts, such as Cambodia [Contribution 8]. The study identifies several barriers to improved governance, including fragmented sectoral responsibilities, weak coordination among agencies, and limited community participation. Through case studies of farmer water user groups and fisheries, the research shows that current, often top-down, management strategies do not always address local realities and can unintentionally worsen competition and conflict over resources. The study recommends integrating water governance at the district level to promote both sustainability and social equity.

3. Conclusions

This Special Issue of Water not only presents recent advances in water resource assessment but also offers an extensive view of water resource management issues, ecological risk analysis, and sustainable management in drylands. By drawing on diverse case studies from Asia and beyond, the collected studies provide a foundation for integrated solutions that address competing demands and foster resilience in vulnerable dry environments. As global water challenges intensify, ongoing collaboration among scientists, policymakers, and communities will be essential to advancing both understanding and actions. We sincerely thank all the authors, reviewers, and editorial staff for their contributions to this Special Issue. We hope these findings and perspectives will encourage further research, innovation, and dialogue on the path to sustainable water and ecological management.