Initiatives on exploring the mechanism of eco‐hydrological response to land surface change and adaptive regulation in the Yellow River Basin

The Yellow River Basin faces water scarcity and ecological fragility. Changes on the land surface, characterized by large‐scale soil and water conservation measures, have a significant impact on river runoff and ecological environment. However, there are still great uncertainties in the scientific understanding of the mechanisms by which multiple driver impact eco‐hydrological processes due to the diversity of land surfaces and the complexity of the coupling processes. As an international scientific frontier on interdisciplinary studies in climatology, hydrology, ecology, and other related fields, it is significant to study the mechanisms and assess the impacts of land surface change on eco‐hydrological risk to support ecological restoration plan and sustainable water resources utilization in the Yellow River Basin. Taking the Yellow River Basin as the study area, this study proposes several important research initiatives, focusing on addressing the ecological and water resources problems in the Loess Plateau. These initiatives include (1) to quantify the individual effect of land surface elements (e.g., vegetation, terraces, and check dam) and reveal the nonlinear driving mechanisms of multiple drivers on eco‐hydrological processes; (2) to construct a distributed eco‐hydrological model that couples dynamic land surface features, and simulate eco‐hydrological processes in a changing environment; (3) to improve the ecological risk assessment indicator system and methods for assessing the impacts of land surface changes on eco‐hydrological synergistic functions and ecological risk; (4) to establish an ecological regulation model based on multiobjective game theory and adopt an adaptive regulation mode for ecological risk management. The research could enrich the scientific understanding and theory of eco‐hydrology, and prompt disciplinary studies of ecology, hydrology, climatology, and other fields. The expected academic achievements will innovate eco‐hydrological simulation and assessment techniques in a changing environment, and strongly support the implementation of the national strategy for ecological protection and high‐quality development in the Yellow River Basin.


Abstract
The Yellow River Basin faces water scarcity and ecological fragility. Changes on the land surface, characterized by large-scale soil and water conservation measures, have a significant impact on river runoff and ecological environment. However, there are still great uncertainties in the scientific understanding of the mechanisms by which multiple driver impact eco-hydrological processes due to the diversity of land surfaces and the complexity of the coupling processes. As an international scientific frontier on interdisciplinary studies in climatology, hydrology, ecology, and other related fields, it is significant to study the mechanisms and assess the impacts of land surface change on eco-hydrological risk to support ecological restoration plan and sustainable water resources utilization in the Yellow River Basin. Taking the Yellow River Basin as the study area, this study proposes several important research initiatives, focusing on addressing the ecological and water resources problems in the Loess Plateau. These initiatives include (1) to quantify the individual effect of land surface elements (e.g., vegetation, terraces, and check dam) and reveal the nonlinear driving mechanisms of multiple drivers on eco-hydrological processes; (2) to construct a distributed eco-hydrological model that couples dynamic land surface features, and simulate eco-hydrological processes in a changing environment; (3) to improve the ecological risk assessment indicator system and methods for assessing the impacts of land surface changes on eco-hydrological synergistic functions and ecological risk; (4) to establish an ecological regulation model based on multiobjective game theory and adopt an adaptive regulation mode for ecological risk management. The research could enrich the scientific understanding and theory of eco-hydrology, and prompt disciplinary studies of ecology, hydrology, climatology, and other fields. The expected academic achievements will innovate eco-hydrological simulation and assessment techniques in a changing environment, and strongly support the implementation of the national strategy for ecological protection and high-quality development in the Yellow River Basin.
K E Y W O R D S eco-hydrological model, eco-hydrological processes, ecological regulation, land surface change, risk assessment

| INTRODUCTION
The Yellow River Basin (YRB) has experienced significant changes to its land surface, resulting in a drastic reduction in observed runoff. This poses significant challenges for sustainable water resource development, and significantly impacts the stability, growth, and progress of both the economy and society. Moreover, the YRB faces ecological vulnerability due to water scarcity, with a mere 49 billion m 3 of natural runoff annually. To address the issue, the region has initiated extensive remediation projects since the 1960s and 1970s, implementing 6.08 × 10 4 km 2 of terraced fields, 12.64 × 10 4 km 2 of soil and water conservation forests, and constructing 58,100 check dams by 2020 (Yellow River Conservancy Commission [YRCC], 2021). However, despite these efforts, the observed streamflow at the Huayuankou station on the YRB decreased by 33% from 2000 to 2018 compared to 1956 to 2000 . Furthermore, water resources usage and consumption in the basin exceeded 80% by 2020 (Liu, 2020). Thus, water scarcity remains the most significant challenge facing the sustainable development of YRB's economy and water resources amid land surface changes (Cao & Zhang, 2020).
The land surfaces in the YRB exhibit remarkable complexity and diversity, and their differential changes may result in distinct and significant impacts on the ecohydrological processes of the watershed. The resulting effects of these land surface changes are considered to be one of the leading topics of interest and a cutting-edge scientific issue globally. Furthermore, the extent and intensity of land surface changes are further influenced by increasing human activities, as rapid economic and societal development continues (Liu et al., 2017). Various land surface conditions, such as terrace construction, vegetation transformation, urbanization, and water conservancy projects, can significantly affect the hydrologic response of a watershed (Mosquera et al., 2022;Wang et al., 2021;Xiao et al., 2016). However, the mechanisms and magnitudes of the effects produced by these factors on eco-hydrological processes differ substantially, and their combined impacts on water yield and runoff are even more intricate, necessitating a comprehensive understanding of their interactions (Liu et al., 2021).
The 50th anniversary of Water Resources Research (WRR), organized by the American Geophysical Union (AGU), offered a comprehensive overview and discussions on the progress and future prospects of hydrological research. The event emphasized that the influence of land surfaces on eco-hydrological processes has been, and will continue to be, the focal point of research in the hydrology field (Montanari et al., 2015). Among the 23 scientific challenges in hydrology identified by the International Association of Hydrological Sciences (IAHS), the effect of land surface change on hydrological extremes remains a subject that requires extensive investigation (Blöschl et al., 2019). In April 2022, the United Nations Educational, Scientific, and Cultural Organization (UNESCO) approved the ninth phase of the intergovernmental hydrological program (IHP-IX, 2022-2029, emphasizing water safety science in a changing environment (UNESCO, 2022). This new research phase aims to address the critical concerns of water resource management in the face of environment change. The implementation of innovative programs, such as the International Geosphere-Biosphere Programme/ Biospheric Aspects of Hydrological Cycle (IGBP/BAHC) and the World Climate Research Programme/Global Energy and Water Cycle Experiment (WCRP/GEWEX), has advanced the study of eco-hydrological processes and the effects of alterations in land surface to the forefront of interdisciplinary international research. These programs have greatly advanced our understanding of the complex interactions between land surface, vegetation, and water resources, enhancing our ability to manage these vital resources sustainably.
Investigating the eco-hydrological changes caused by land surface changes and their potential driving mechanisms in the YRB is a national strategic priority in China. This research provides scientific support for watershed ecological protection and high-quality development. Given the YRB's vital role in China's economic and social development, as well as ecological security, the Central Committee of the Communist Party of China and the State Council issued the "Outline of the YRB Ecological Protection and High-quality Development Plan" in October 2021. This plan emphasizes the need to strengthen upstream water source conservation capabilities, develop a midstream soil and water conservation system, and promote water resources conservation and intensive utilization across the entire basin. The Ministry of Ecology and Environment, along with four other departments, issued the "Ecological Environment Protection Plan for the YRB," which identifies "promoting the coordinated management of the three waters and the treatment and restoration of the aquatic ecological environment" as one of its seven major tasks. To support China's national strategy for ecological protection and high-quality development of the YRB, it is crucial to achieve water resource conservation and intensive utilization. This can be accomplished by clarifying the driving mechanisms behind surface changes on hydrological and ecological processes and systematically evaluating the coevolution effects of these changes on eco-hydrological processes. Such efforts will provide significant scientific support to the Ecological Protection and High-Quality Development Plan of the YRB in China.

| State-of-the-art literature review
Investigating the ecological and hydrological responses to land surface change is not only a core issue in hydrological research but also the fundamental foundation for understanding the interactions between hydrological processes and ecological systems at various spatial and temporal scales (Liu et al., 2014a). Since the 1960s and 1970s, numerous large-scale engineering projects have been constructed in the middle reaches of the YRB (Fu et al., 2011;Shi & Shao, 2000). These projects primarily focused on soil and water conservation in the channel and slope of the hydraulic engineering sites, altering the region's hydrological and ecological processes (Yang et al., 2020). For example, field data collected from the Loess Plateau shows that bench terraces can reduce surface runoff by 70%-90% and sand sediment by 90%-100% (Liu et al., 2014b). Changes in vegetation coverage is an important indicator of land surface change. Enhancing slope vegetation coverage through ecological restoration projects can effectively intercept rainfall, reduce surface runoff and sand sediment, and mitigate water and soil erosion processes (Liu et al., 2017). However, some studies have found that shift in land use from cropland to forest and/or grassland in semi-arid areas can increase vegetation coverage. This increase in vegetation coverage may lead to heightened vegetation transpiration and water consumption, resulting in a noticeable reduction in surface runoff, soil water content, and ultimately river flow. Consequently, this could increase ecological risk downstream of the river basin (Jia et al., 2017;Zhang et al., 2018).
Previous studies have acknowledged the impact of land surface changes on surface runoff Zhang et al., 2020). Specifically, some studies have proposed several attribution identification methods to quantitatively assess the impacts of various driving factors on ecological and hydrological processes (Dey & Mishra, 2017;Wang et al., 2008). However, these attribution identification methods typically rely on the linear summation of multiple driving forces, limiting their ability to account for the synergistic and nonlinear effects present in hydrological and ecological processes. Consequently, it is important to develop advanced eco-hydrological models that can accurately examine the nonlinear and synergistic behaviors in hydrological and ecological processes.
Eco-hydrological models that quantitatively describe the complex and dynamic relationships between vegetation and water under changing environments are essential for understanding the interactions between ecological and hydrological systems Rinaldo et al., 2014;Tague & Frew, 2021). Based on model complexity with respect to the representation of vegetationhydrological interactions, eco-hydrological models can be categorized into conceptual models, semi-physically based models, and physically based models (Luo & Zuo, 2019;Guswa et al., 2020). Conceptual models primarily rely on the concept of hydrological models and incorporate empirical crop growth modules to establish simple and empirical functions for calculating vegetation growth (Gao et al., 2018;Xu & Zhao, 2016). These models typically lack mechanistic descriptions of plant growth and vegetationhydrological interactions . In contrast, semi-physically based models and physically based models apply physiological and ecological processes to describe plant physiological processes (e.g., photosynthesis and evapotranspiration) (Yohannes et al., 2021). However, these models are usually computationally intensive, and their development requires various physiological and morphological parameters (e.g., electron transmission rate, plant canopy height), which may be difficult to obtain (Knighton et al., 2020). To overcome the limitations of existing models and better understand the nonlinear and synergistic behaviors in hydrological and ecological processes, researchers should focus on the development of more advanced eco-hydrological models. These models should incorporate a balance between complexity and usability, effectively describing the intricate interactions between vegetation and water while minimizing the need for extensive computational resources and hard-to-obtain parameters. This would enable a more comprehensive understanding of the impacts of land surface changes on eco-hydrological processes, which is vital for effective water resource management and sustainable development.
Vegetation significantly influences various aspects of hydrological cycles, while simultaneously being affected by hydrological processes, ecological processes, and ecohydrological interactions (Wang et al., 2018;Williams et al., 2016). Enhancing the coupled simulation of hydrological and ecological processes is a central challenge in the interdisciplinary research of climate, hydrology, and ecology. Due to the scarcity of land surface and subsurface monitoring data, there is a pressing need to strengthen our understanding of hydrological and ecological coupling mechanisms. The rapid advancements in remote sensing and machine learning technologies offer promising opportunities for utilizing multisource information to facilitate intelligent coupling and simulation of hydrological and ecological processes, which is a crucial research direction in hydrological and ecological sciences.
The construction and operation of hydraulic engineering projects provide significant social and economic benefits. However, they may also alter natural river flow regimes and affect ecological conditions in river basin. Notably, the operation of reservoirs can mitigate the adverse effects of hydraulic engineering projects on river ecology (Dong & Sun, 2007;Wu et al., 2019). Ecological reservoir operation models can be categorized into three types based on how ecological factors are incorporated: constraint-based operation, target-based operation, and value-based operation (Chen et al., 2011;Sabo et al., 2017). Constraint-based reservoir operation models share similarities with conventional models and are widely used. A key limitation is that while ecological constraints are included, the range of feasible ecological flow solutions may remain extensive, leading to large variances between different ecological objectives (Wang et al., 2019). Target-based reservoir operation models quantify ecological risks and/or benefits, incorporating them into operation rules with the aim of maximizing ecological benefits and/or minimizing ecological risks. A challenge with this approach is the way to accurately and effectively represent ecological risks and/or benefits. Value-based models utilize an economic approach to attain ecological benefits, monetizing all goals to guide reservoir operations toward meeting ecological objectives (Bryan et al., 2010). Among the three types of models, target-based and value-based models offer more flexibility in model construction and can take into account various benefits and risks. However, a challenge is that reservoir operation outcomes are typically sensitive to operational goals (Chen et al., 2011), making it difficult to obtain robust and reliable reservoir operation solutions.
As technological advancements lead to more intensive human activities in the future, ecological and hydrological processes will be increasingly impacted by these activities (Evaristo & McDonnell, 2019;. Reservoir operation, an important human activity and engineering measure designed to mitigate adverse environmental effects, has multiple objectives (Dabhade & Regulwar, 2021). It is crucial for basin managers to identify the sources and causes of ecological risks, evaluate the ecological impacts of land surface changes, and develop comprehensive reservoir operation strategies that consider the competition and cooperation among multiple water use sectors. This approach will help enhance environmental protection and promote high-quality river basin development.
2.2 | Scientific issues associated with land surface changes and ecological and hydrological processes 2.2.1 | Impacts of land surface change on the synergy of ecological and hydrological functions Land surface change serves as a crucial impetus influencing both hydrological and ecological dynamics in watersheds. Modifications to the land surface, including the construction of terraced fields and impoundment dams, can affect regional hydrological cycles by altering runoff generation, infiltration, and evaporation processes. Vegetation cover, a vital ecological indicator, can be significantly influenced by a wide range of hydrological factors, such as soil moisture content. As land surface undergoes changes, hydrological and ecological processes in watersheds engage in complex interactions that jointly influence river runoff and the availability of regional water resources. Consequently, there is a pressing need for rigorous scientific inquiry into the interrelated functions of hydrological and ecological processes, encompassing the enhancement of ecological base flow, facilitation of economic development, and amelioration of the regional ecological environment. A comprehensive understanding of the impact mechanisms of land surface changes on hydrology, ecology, and their synergistic functions is indispensable for informing watershed ecological restoration and governance strategies, while bolstering watershed carrying capacity and system resilience.

| Mechanism of ecological risk evolution under multiple nonlinear driving forces
The spatial and temporal distribution of the risk in ecological systems is intricately linked to land use patterns.
Factors such as climate change, large-scale soil and water conservation measures, and accelerated urbanization can lead to alterations in land use and land cover patterns. These changes subsequently impact regional hydrological and ecological processes, habitat connectivity, and biomass, culminating in shifts in the spatial and temporal attributes of ecological system risk. Nevertheless, the response of ecological risk to distinct driving factors demonstrates marked nonlinearity. Consequently, there is a pressing need to delve into the nonlinear effects of multiple driving forces on the evolution of ecological system risk. Specifically, it is essential to direct research efforts toward the quantitative identification of disparate driving factors and their cumulative impacts on ecological system risk. Such investigations can lay the groundwork for effective ecological risk management and provide the basis for informed ecological preservation and high-quality development strategies.

| Competition and cooperation of multiple water use sectors in reservoir operation
Alterations in land surface patterns and hydrological conditions have profound impacts on river runoff, potentially modifying the input and boundary conditions for the operation of multireservoir systems. Conversely, the operation of such reservoir systems can influence the spatial and temporal distribution of river flow, consequently altering hydrological and ecological processes in the watershed. Thus, the operation of multireservoir systems constitutes a multiobjective decision-making challenge that encompasses natural processes, engineering infrastructure, and decision-makers. In the competition between multiple water use sectors for limited water resources, it is important to investigate the feedback and adaptive mechanisms of reservoir systems in response to changes in land surface and hydrological conditions. These research endeavors could enhance the ecological service capacity of multireservoir systems, facilitate mutually agreeable solutions among competing water use sectors, and promote the efficient and sustainable development of a watershed's socioeconomic and ecological conditions.

| The YRB
The YRB, China's second largest river in terms of drainage area, originates from the Bayan Har Mountain in the Tibetan Plateau and traverses nine provinces (i.e., Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, and Shandong)-before ultimately converging with the Bohai Sea at Dongying city. Encompassing a drainage area of approximately 752,443 km 2 , the river spans a total length of 5464 km. The upper Yellow River is primarily situated within the Tibetan Plateau, characterized by high elevation and a fragile environment for sustaining life, whereas the middle Yellow River is located in the Loess Plateau, where soil erosion poses a significant environmental concern. Since the 1970s, the YRCC has implemented large-scale soil and water conservation measures on the Loess Plateau, resulting in changes to the land surface and, consequently, alterations to the regional water cycle and runoff yield mechanisms.
Due to the harsh environmental conditions for sustaining life in the Tibetan Plateau, land surface changes in the upper reaches are predominantly driven by climate change, whereas those in the middle reaches are primarily governed by human activities. These activities are characterized by the construction of terraces, reforestation efforts, and the building of check dams, among others, in the Loess Plateau. It is thus imperative to examine the ecohydrological responses to land surface changes, focusing on the Loess Plateau and extending the scope to the entire YRB, ranging from experimental stations to subcatchments and the entire river basin. Figure 1 depicts the river system, the locations of the experimental station, the selected subcatchment, and the large-scale reservoirs in the Yellow River.

| Research tasks
Centered on the theme of "investigating the impact mechanisms and assessment of land surface changes on eco-hydrology in the YRB," the initiatives comprise four research components, following a logical progression of "mechanism analysis, model construction, impact assessment, and risk regulation." Figure 2 illustrates the logical relationships between the research tasks and the key scientific issues. The details of the research tasks are presented as follows: 3.2.1 | Unveiling the impact mechanisms of diverse land surfaces on eco-hydrological processes Utilizing observation data from runoff plots at the three experimental stations (i.e., Tianshui, Xifeng, and Suide) in the YRB, the study will analyze rainfall-runoff processes in the experimental areas with varying land surface types. It will examine the impacts of various land surface conditions on the rainfall-runoff relationship and explore the driving mechanism of soil and water conservation measures (e.g., vegetation, terraces, and check dams) on eco-hydrological processes.
By selecting typical subcatchments that take into account climate, geomorphology, and human activity characteristics, the study will analyze the spatial patterns and temporal changes of the land surface. It will diagnose the trends and statuses of key eco-hydrological variables under composite land surface conditions and investigate the responses of eco-hydrological processes to precipitation at different stages.
Based on the observed responses of eco-hydrological processes to precipitation above single and composite land surfaces, the study will propose a method for identifying the nonlinear contributions of multiple driving forces to eco-hydrological processes. This will quantify the impacts of different land surfaces on eco-hydrological variables in medium-to-large-scale river basins and unveil the synergistic effects of changes in land surface conditions on eco-hydrology.
3.2.2 | Developing a high-resolution, distributed eco-hydrological model based on diverse land surfaces The YRB will be gridded, taking into account the basin scale and topographic features. A grid-based climatic F I G U R E 1 The river system and locations of the experimental station, the selected subcatchment, and the large-scale reservoirs of the Yellow River. ZHANG ET AL.
forcing database and a land surface parameter database will be established. The climatic forcing database will be created by assimilating multisource meteorological products, while the land surface parameter database will rely on multisource remote sensing information. Using these two databases, a digital river system and its topological relationships will be constructed.
Considering the effects of different land surfaces, such as vegetation, terraces, and silt dams, on eco-hydrological processes, the VIC model's modules for water storage and release, vegetation ecological processes, infiltration, and runoff generation will be enhanced. The improved VIC model will be applied to investigate the coupling characteristics between hydrological and ecological processes. An index set will be introduced to quantify land surface conditions, including vegetation, terraces, and silt dams. The correlations between land surfaces and model parameterizations will be analyzed, and a regionalization scheme for land surface parameters will be proposed. The study will explore meta-learning, selfadaptive methods for coupling water cycle and ecological processes at the basin scale, ultimately achieving distributed simulation of surface hydrology-ecology interactions and waterenergy interactions.

| Quantifying the impacts of land surface changes on eco-hydrological synergistic functions and ecological risks
Utilizing an intelligent terrain target recognition algorithm and multisource/multiphase remote sensing images, the study will interpret and produce the land cover data set for the YRB for the past 30 years. By combining research data from the basin, the spatio-temporal evolution of land surfaces (e.g., forest land, terraced fields, grasslands, and urban construction land) will be systematically analyzed.
Employing the distributed eco-hydrological model from previous steps, the study will simulate the eco-hydrological processes under dynamic land surface conditions and analyze the evolution characteristics of multidimensional hydrological and ecological factors. To safeguard the basin's ecosystem and ensure downstream ecological base flow, the study will clarify the eco-hydrological synergistic functions of the basin and investigate the impacts of land surface changes on these functions.
Based on the spatio-temporal evolution of multiple ecohydrological factors in a basin, a multiobjective index will be constructed to quantify the ecological risks, taking into account the basin characteristics. This will enable the analysis of the spatio-temporal coupling between environmental changes and ecological risk evolutions. To enhance the ecological risk assessment system, the study will identify the sources of land and river ecology risks and determine the key ecological stress factors and their significance. Finally, the study will evaluate the impacts of dynamic land surface changes on eco-hydrological synergistic functions and ecological risks.

| Developing risk control plans and adaptation strategies based on multiobjective ecological regulation
The study will quantify and characterize the ecological objectives and comprehensive benefit objectives of reservoir groups. It will analyze the prioritization of objectives in different temporal (wet season, dry season) and spatial (midstream, downstream) stages, construct, and solve the ecological operation model of reservoir groups, considering multiple stakeholders and objectives. By analyzing the equilibrium set and the multiobjective Pareto frontier, the study will quantitatively explore the mechanism through which ecological objectives affect the comprehensive utilization benefits of reservoir groups and the ecological benefits of the basin.
Boundary conditions will be created based on the synergistic law of land surface and eco-hydrology to solve the multiobjective ecological operation scheme of reservoir groups under different scenarios (combinations of land surface and inflow). The study will evaluate the achievement of utilization objectives and ecological objectives of reservoir groups under various scenarios. It will also assess the gaming laws between ecological objectives and beneficial objectives, and different types and regions of ecological objectives. The study will propose an ecological operation scheme for reservoir groups that can adapt to changes in land surface and hydrological dynamics.
The study will quantify the chain response mechanism of "land surface elements-reservoir group operationecological risk" to systematically evaluate the impacts of land surface and river channels on land surface elements and reservoir operation methods. Based on the concept of opportunity cost, several measures will be proposed to improve land surface ecology and protect the base flow of river channels. These measures will provide technical and decision-making support for basin ecology and the synergistic development of socio-economy.

| Expected innovations
3.3.1 | Unveiling the mechanisms of complex land surface changes' impacts on hydro-ecological processes in watersheds and quantifying the nonlinear attributions of hydro-ecological changes Land surface changes due to human activities (such as terrace construction and water conservation projects) significantly affect hydro-ecological processes in the YRB. Although considerable progress has been made in understanding the effects of human activities on watershed hydrological cycles, further research is needed to explore how different land surface conditions interact to impact hydro-ecological processes. This project aims to provide important theoretical innovation by revealing the driving mechanisms behind hydro-ecological process evolution under the influence of multiple land surface changes and quantifying the nonlinear responses of these processes to composite land surface alterations.
3.3.2 | Developing a distributed hydroecological coupling model based on land surface conditions to analyze the quantitative impacts of land surfaces on hydro-ecological synergistic functions and ecological risks Variations in land surface conditions complicate hydroecological processes, making the interactions between hydrological and ecological processes critical based on a watershed's water and energy balance. These changes increase spatiotemporal heterogeneity and complexity of synergistic service functions, potentially leading to heightened regional and riverine ecological risks. Key questions include how to quantify the spatiotemporal characteristics of multiple land surface factors and how to construct nonlinear physical connections between hydrological characteristics and ecological processes under the spatial heterogeneity of land surfaces. To address these questions, this project aims to develop a distributed hydro-ecological coupling model based on dynamic land surface conditions for quantitatively analyzing the impacts of land surface changes on hydro-ecological synergistic functions and ecological risks, providing critical methodological innovation.
3.3.3 | Constructing an ecological operation model for reservoir groups oriented toward multiagent competitive and collaborative processes, and proposing ecological risk control strategies The reservoir groups in the middle and lower reaches of the Yellow River serve multiple purposes, including flood control, downstream siltation prevention, domestic and agricultural water supply, and power generation. Under varying land surface conditions, runoff has declined rapidly, and the relationship between water and sediment has changed. To achieve national strategic goals for ecological protection and high-quality development in the YRB, it is crucial to build a dynamic ecological risk evaluation model based on the "hazard-vulnerability-loss risk" chain transmission mechanism. By clarifying the joint effects of land surface changes, hydro-ecological effects, and water conservancy engineering operations on basin ecological risk evolution, this project aims to propose a reservoir group regulation model for multiregion, multiobjective, and multivariable competitive and collaborative processes. This model seeks to establish a selfadaptive and balanced regulation scheme between basin ecological risks and systematic utilization benefits, offering vital technological and applied innovation.

| CONCLUSIONS AND SUMMARY
With the rapid development of the society and economy, land surfaces have undergone significant changes due to various intensive human activities aimed at improving wellbeing. Changes in land surface not only influence the ecological system but also alter regional hydrological processes. It is essential to study the eco-hydrological effects of land surface changes to support environmental protection and river basin management.
Based on a state-of-the-art literature review on land surface changes and their impact on ecological and hydrological processes, future studies should focus on revealing the nonlinear driving mechanisms of multiple factors on eco-hydrological processes, constructing a distributed eco-hydrological model that incorporates various dynamic land surface features, enhancing the ecological risk assessment indicator system and methodologies for evaluating the impacts of land surface changes on ecohydrological synergistic functions and ecological risk, and establishing an ecological regulation model grounded in multiobjective game theory.

ACKNOWLEDGMENTS
This research has been financially supported by the National Natural Science Foundation of China (U2243228, 52121006), the National Key Research and Development Programs of China (2021YFC3201100, 2022YFC3205200), and the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering (2022nkzd01, 2021nkz490211). We acknowledge Gaoxia Sun, Zhongrui Ning and Yueyang Wang for preparing figures, editing reference list, and providing supporting materials.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.

ETHICS STATEMENT
None declared.