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The paper presents a historical overview of the development of hydrological models in the former USSR and Russia since the 1930s. An overwhelming number of hydrological papers were published in Russian, and they are not sufficiently well known to the world hydrological community. The purpose of the review is to fill the gap and present the main achievements, some of which were pioneering for their time. The period under consideration is divided into three sub-periods. Pre-computer, the 1930–1950s were associated, first of all, with the development of models of unsteady water flow in river channels and linear flood-routing models; in the 1960–1980s, many theoretical and practical foundations for modelling the processes of the hydrological cycle and the formation of river runoff were developed; and in the Russian era, following 1991, several notable advancements in the considered field were also made. [ABSTRACT FROM AUTHOR]

This study examines the influence of climate change on hydrological processes, particularly runoff, and how it affects managing water resources and ecosystem sustainability. It uses CMIP6 data to analyze changes in runoff patterns under different Shared Socioeconomic Pathways (SSP). This study also uses a Deep belief network (DBN) and a Modified Sparrow Search Optimizer (MSSO) to enhance the runoff forecasting capabilities of the SWAT model. DBN can learn complex patterns in the data and improve the accuracy of runoff forecasting. The meta-heuristic algorithm optimizes the models through iterative search processes and finds the optimal parameter configuration in the SWAT model. The Optimal SWAT Model accurately predicts runoff patterns, with high precision in capturing variability, a strong connection between projected and actual data, and minimal inaccuracy in its predictions, as indicated by an ENS score of 0.7152 and an R2 coefficient of determination of 0.8012. The outcomes of the forecasts illustrated that the runoff will decrease in the coming years, which could threaten the water source. Therefore, managers should manage water resources with awareness of these conditions. [ABSTRACT FROM AUTHOR]

Severe socio-environmental pressures and land degradation are substantially impacting Ethiopia, eventually leading to low agricultural productivity, with a consequent very high rate of poverty and food insecurity. The current study investigates the future effect of four management practices on reducing sediment yield in the Fincha sub-watershed, Ethiopia, by developing a soil and water assessment tool (SWAT) model over the next three decades (2019–2050). Four best management practices (BMPs) largely applied in the region were considered here. It was found that filter strips can decrease the sediment yield by 65.64 and 58.77, soil or stone bund by 76.37 and 73.07, contour farming by 79.79 and 75.86, and terracing by 84.9% and 76.32% for the years 2019 and 2050, respectively. The impact of these BMPs on various hydrological processes also was evaluated using SWAT. It was found that BMPs are effective in reducing surface runoff and water yield and in increasing groundwater and lateral flows, while they have a reduced effect on evapotranspiration, lateral flow and water yield. The findings presented here point out that all the simulated management practices significantly lower surface runoff and consequently sediment yield across the watershed, but they are not effective enough to reduce soil erosion below a critical threshold that assures crop production. Therefore, to achieve tolerable soil loss, additional soil and land management strategies, such as biological measures and a combination of BMPs are needed and should be considered in future investigations. In summary, the current study offers evidence for managing river basins in semi-arid regions, and can help in ensuring sustainable management of natural resources. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrological models serve as effective tools for managing water sources and assessing water components. Although basin hydrological models have been developed, selecting suitable software for modeling specific areas remains challenging. Hence, it's essential to opt for software capable of simulating the hydrological cycle with a simple structure and minimal input parameters. In northwest Iran, AWBM and ARCSWAT software were employed for simulation. AWBM is a simplistic program estimating runoff using precipitation and evaporation indicators, while ARCSWAT is a semi-distributed software for continuous flow simulation. ARCSWAT necessitates various inputs, including geological, land use, and slope maps, along with precipitation, temperature, relative humidity, and radiation statistics. The runoff simulation results during calibration and validation periods were assessed using two statistical indices: Nash Sutcliffe Efficiency (NSE) and the coefficient of determination (R2). A comparison of the statistical indicators revealed NSE values of 0.83 and 0.7 for calibration and validation periods, respectively, and R2 values of 0.83 and 0.8 for calibration and validation periods, respectively, for the semi-distributed SWAT model. In contrast, for the AWBM integrated model in the basin, NSE values were 0.63 and 0.48, and R2 values were 0.48 and 0.48 for calibration and validation periods, respectively, indicating better results in runoff simulation at the monthly time scale. [ABSTRACT FROM AUTHOR]

Comprehensive assessments of hydrological components are crucial for enhancing operational water supply simulations. However, hydrological models are often evaluated based on their surface flow simulations, while the validation of subsurface and groundwater components tends to be overlooked or not well documented. In this study, we evaluated the outputs of two hydrological models, the Large Basin Runoff Model (LBRM) and the Weather Research and Forecasting – Hydrological modeling extension package (WRF-Hydro), for potential implementation in operational water balance forecasting in the Great Lakes region. We examined the simulated hydrological variables including surface (e.g. snow water equivalent, evapotranspiration, and streamflow), subsurface (e.g. soil moisture at different layers), and groundwater components with observed or reference data from ground-based stations and remotely sensed images. The findings of this study provide valuable insights into the capabilities and limitations of each model. These findings contribute to more informed water management strategies for the Great Lakes region. [ABSTRACT FROM AUTHOR]

Changes in hydrological processes in watersheds are triggered by various factors, including land use land cover changes (LULCC) emerging from human activities. Hence, it is crucial to elucidate the interaction among hydrological processes to improve sustainable water management plans. The current study explored the effects of LULCC on hydrological processes in the Gala Lake catchment over a 30‐year temporal period. In this context, to evaluate LULCC, land cover maps were obtained using the supervised classification method with Landsat images (5 TM, 7 ETM+, 8 OLI) of 1993, 2008, and 2023. Hydrological processes were assessed using the Soil and Water Assessment Tool (SWAT), a commonly applied eco‐hydrological model. The model was utilized to evaluate the potential effect of LULCC on processes like surface runoff, infiltration, evapotranspiration, and erosion. Between 1993 and 2023, significant LULCC have been observed in the study area. There has been a decrease of 4.3%, 1%, 1.6%, and 5.3% in agricultural lands, forested lands, inland marshes, and pasture lands, respectively, while artificial surfaces, rice fields, and water bodies have seen an increase of 7%, 3.4%, and 1.9%, respectively. The potential effects of these changes were observed as a decrease in the runoff, a decrease in permeability, and an increase in processes such as evapotranspiration and erosion throughout the basin and sub‐basin. In general, LULCC significantly affect the hydrological status of the catchment. Therefore, establishing different conservation and utilization strategies that consider land use dynamics to maintain the resilience of ecosystems in the basins is vital in the sustainable management of water resources. [ABSTRACT FROM AUTHOR]

Abstract This study examines the influence of climate change on hydrological processes, particularly runoff, and how it affects managing water resources and ecosystem sustainability. It uses CMIP6 data to analyze changes in runoff patterns under different Shared Socioeconomic Pathways (SSP). This study also uses a Deep belief network (DBN) and a Modified Sparrow Search Optimizer (MSSO) to enhance the runoff forecasting capabilities of the SWAT model. DBN can learn complex patterns in the data and improve the accuracy of runoff forecasting. The meta-heuristic algorithm optimizes the models through iterative search processes and finds the optimal parameter configuration in the SWAT model. The Optimal SWAT Model accurately predicts runoff patterns, with high precision in capturing variability, a strong connection between projected and actual data, and minimal inaccuracy in its predictions, as indicated by an ENS score of 0.7152 and an R2 coefficient of determination of 0.8012. The outcomes of the forecasts illustrated that the runoff will decrease in the coming years, which could threaten the water source. Therefore, managers should manage water resources with awareness of these conditions.

[Objective] To analyze the scale-dependent relationships between daily sediment yield and key environmental factors and to explore effective prediction method to cope with the prediction challenges caused by the complexity of sediment transport mechanisms and the nonlinearity of hydrological processes. [Methods] Employing the Composite Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) approach, we analyzed the multi-temporal scale variability characteristics between daily sediment yield and five potential influencing variables (flow rate, precipitation, average temperature, potential evapotranspiration, and NDVI) in the controled regions of four hydrological stations in the Fu River basin of Southwest China from 2013 to 2018. Interactions between daily sediment yield and related variables at different temporal scales were identified, upon which predictions of daily sediment yield were predicted. [Results] The CEEMDAN method successfully decomposed the daily sediment yield and its potential influencing variables into 10-11 intrinsic mode functions (IMFs) and residual item, revealing the significant changes of the daily sediment yield at different temporal scales ranging from 3 to 730 days. After decomposition, daily sediment yield showed significantly enhanced correlation with howrate and precipitation across all temporal scales, whereas temperature, potential evapotranspiration, and NDVI were primarily significantly correlated with long-term scale sediment yields. By using stepwise multiple linear regression to predict the daily sediment yield, the prediction performance of the model is significant, and the R2 values exceeds 0.55 at all stations. [Conclusion] The CEEMDAN method effectively revealed the scale dependency between sediment yield and its influencing variables, offering a new perspective for understanding the dynamics of river sediment transport.

The consequences of human interventions on land use have been empirically demonstrated to affect substantially hydrological processes and ecosystem services within watershed environments. Since 1970, Malaysia has faced deforestation, driven mainly by logging and agricultural expansion, aligning with its developmental goals by 2020. From 1970 to 2000, deforestation led to a 25.5% decline in forested land, causing a significant 10.2% rise in excess runoff. Moreover from 2001 to 2021, the nation lost 17% of its total land to deforestation. These trends emphasize the need for a thorough investigation of sustainable conservation efforts in Malaysia. This study focuses on the Langat basin in Malaysia, evaluating past and future land use changes and their effects on the basin’s hydrological response. The study employed key informant reports, population growth data, observed land use change, field survey and agricultural land availability considered for developing change scenarios. We emphasized the significance of integrating diverse modeling methods to analyze LULC changes effectively. The use of a semi-distributed hydrological model, SWAT, in combination with Markov chain and Multi-Layer Perceptron (MLP) model and Geographic Information Systems (GIS) techniques proved to be an integrated and suitable tool for comprehensive change analysis and modeling of land use. Markov chain modeling is valuable for predicting land use changes over time, providing input scenarios for SWAT simulations. MLP is a powerful algorithm to capture non-linear relationships and complex patterns in the data, enhancing the modeling accuracy. The simulation results, based on historic land use data (1984-2006-2010) and projected future land use maps (2030-2050-2080), revealed a consistent pattern of urban expansion and deforestation leading to increased streamflow. Projections indicated a substantial rise in streamflow by 20%, 61%, and 71% for the 2030s, 2050s, and 2080s, respectively. To mitigate potential flood and sediment loss, it is crucial to involve local stakeholders such as local communities, government bodies, environmental organizations, and businesses. Such analysis facilitates understanding their perspectives and concerns regarding afforestation and urban expansion control, informing future development programs and land use planning effectively.

The article explores the Soil and Water Assessment Tool (SWAT), its features, applications and advancements that propelled the use of this hydrological modelling tool. Topics discussed include runoff modelling using SWAT, sediment yield modelling, nutrient cycle modelling, and limitations such as the need for extensive input data, simulation of runoff and sediment in certain months, and performance depending on the specific characteristics of the watershed being studied.

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The introduction of nature‐based solutions (NbS) in catchments has the potential to increase the cost‐effectiveness, flexibility, and reliability of water management practices aimed at improving water security. However, the scientific‐evidence base of the hydrological impacts of NbS is still weak, and there is therefore a risk that catchment interventions might not lead to the desired hydrological outcomes. This is especially important when assessing NbS‐based catchment interventions before their implementation, as this requires robust simulation tools capable of effectively managing the uncertainties associated with future forecasts. This study aims to review the hydrological impacts of different NbS intervention types for water management. First, we present an NbS typology and the corresponding dominant hydrological impacts. We then use this typology to review the strength of the current evidence of the effect of NbS interventions on the hydrological response at the catchment‐scale. Our results demonstrate that the effectiveness of each NbS type hinges on specific conditions such as location, design, and environmental factors. For instance, micro‐reservoirs notably enhance surface storage and evaporation, while infiltration trenches reduce runoff but can increase soil erosion. Our global analysis highlights the need for an improved understanding of NbS catchment impacts and careful planning of NbS interventions as a key for successful long‐term implementation of NbS. These include participatory approaches with stakeholder involvement in NbS co‐design, knowledge co‐production, and novel data collection to support locally relevant adaptation strategies, and to increase water security on the long term.This article is categorized under: Science of Water > Hydrological Processes Engineering Water > Planning Water Water and Life > Conservation, Management, and Awareness [ABSTRACT FROM AUTHOR]

The history of experimental hydrology in China is important but poorly documented. Here we review 94 papers (86 of these in Chinese) from the CNKI and Web of Science websites to chronicle the history of experimental studies in China before 2000. Professor Wei‐Zu Gu—the focus of this Special Issue—factors heavily into this history. Perhaps more than any country, the experimental hydrology history of China is influenced by socioeconomic development and political change. Our analysis shows 4 main periods of development associated with (1) an early development stage before 1949, the founding year of People's Republic of China (PRC), (2) an initial period of rapid transition in experimental studies in China (1949–1965), (3) a struggling and recovering stage for during and shortly after the Cultural Revolution, from 1965 to 1978, and (4) significant progress associated with new policies for reform and opening up in China from 1978 to 2000, that included contributions of Wei‐Zu Gu and other scientists. In terms of experimental hydrological findings, two notable contributions are a mathematical description of saturation overland flow derived from streamflow and precipitation data and calculated water storage deficit in the unsaturated zone by Zhao and Zhuang (1963), several years before its process‐based 'discovery' in the USA (and elsewhere) and the 'interface runoff generation law' of Yu (1985) which was ahead of its time in understanding linking the notion of the commonality of all runoff forms. In terms of model development stemming from experimental studies, the development of the Xinanjiang Model of Zhao (1980) was a significant achievement, later partly adopted into the VIC model in the USA and the ARNO model in Europe. Finally, the Hydrohill catchment developed by Wei‐Zu Gu led the way for the rapid rise in process studies and internationalization of experimental hydrology in China. Overall, the experimental hydrological studies from 1949 to 2000 had a strong engineering focus, with many links to water conservation construction and management. [ABSTRACT FROM AUTHOR]

Semiarid regions play a pivotal role in global ecosystem and environmental governance. Changing environment (climate and land use variation) has led to the disruption of hydrology in semi-arid regions and ecological degradation in some area. Understanding their hydrological response to changing environments is crucial for ecological rehabilitation and optimal water resource allocation. This research, conducted in a Chinese semiarid watershed, integrates multi-field models about hydrology, meteorology and geography to investigate hydrological processes in typical hydrological years. The results indicate that the climate in this region is drying, and the likelihood of extreme weather events is increasing with global warming. Projecting changes from 2010 to 2060, 9.21% of grassland converting to 5.63% of forest and 3.58% of gully built-up land. As a result, the flood peak increases by 22.99% in typical drought years, while it decreases by 36.77% in normal years. Based on our analysis of the rainfallrunoff process in typical drought and normal years, we identify two distinct effects: the "local rainfall-runoff effect" and the "global rainfall-runoff effect", respectively. However, in typical wet years, the streamflow state is primarily controlled by intense and concentrated precipitation. This research provides insights into the effect of ecological restoration and typical climate variations on hydrological cycle in semiarid regions, thus contributing to more informed decision-making in environmental management and water resource planning. [ABSTRACT FROM AUTHOR]

Hydrological models can benefit from soft calibration, a process by which the proper simulation of hydrological variables is proved while or before addressing hard calibration. Soft calibration reduces the probability of obtaining a statistically accurate but unrealistic model. However, it requires soft data, which is often hard to acquire or unavailable. This work presents HydRoVars, an R tool developed to facilitate the estimation of data which can be implemented in a soft calibration procedure. It allows us to estimate two key hydrological indices (the runoff coefficient and baseflow index) and weather-related variables at the catchment scale for one or numerous basins. The runoff coefficient is calculated automatically from precipitation and streamflow datasets. Groundwater contribution is estimated through a semi-automatic process based on a baseflow filter which considers hydrogeological properties. Modellers would benefit from incorporating soft calibration in their calibration procedures, and this tool might help to estimate these relevant hydrological variables in their modelled area. The tool has been tested in 19 subbasins of the Tagus River basin (Spain) located in different geological regions. In the test cases, we demonstrate the usefulness of this tool to improve the model representation and gain an understanding of the catchments' hydrology. HIGHLIGHTS An R tool has been developed to collect weather and hydrological variables.; It allows estimating the runoff coefficient, and the baseflow index at the catchment scale.; Runoff coefficient can be automatically obtained for multiple basins.; Guidance is provided for a realistic groundwater contribution estimation.; Its usefulness has been tested in the Upper Tagus River basin (Spain).;

A hydrological model should be ideally calibrated and evaluated regarding both the representation of the streamflow and the intermediate hydrological processes. A challenging aspect is the poor spatial and temporal representativeness of in-situ measurements of these processes. This research evaluated the benefit of incorporating actual evapotranspiration (AET) estimates from two remote sensing (RS) data sources for calibrating a large-scale hydrologic model applied to a Brazilian Semi-Arid basin. Both spatially averaged and spatially distributed approaches were tested, and single—(only streamflow or only AET) and multi-variable calibration (streamflow and AET) procedures were used. Incorporating AET from MOD16 (MODerate-resolution Imaging Spectroradiometer product 16) did not help improve hydrological model performance independently of the calibration configuration. The introduction of AET estimates from GLEAM (Global Land Evaporation Amsterdam Model) as a calibration variable led the hydrological model to reproduce these AET values closer and simultaneously better represent the observed streamflow. The findings of this research highlight the benefit of incorporating AET as a calibration variable for improving the overall hydrologic model performance, which can even outperform the calibration based solely on streamflow. However, there is the need to test different calibration configurations and distinct RS data sources, which may result in very contrasting results. [ABSTRACT FROM AUTHOR]

This study evaluated the impact of land-use land-cover (LULC) change (LULCC) on the hydrologic processes of the Manafwa Basin in eastern Uganda using the Soil and Water Assessment Tool (SWAT) model. Model inputs included the 1995, 2008, and 2017 LULC maps; digital elevation model; and soil, climatological, and hydrologic data. The Calibration and Uncertainty Program Sequential Uncertainty Fitting algorithm was used to calibrate and validate the SWAT model. The model was validated for 2011 to 2013 using daily river discharge. Model statistical measures obtained during calibration and validation ranged from 0.79 to 0.94 for coefficient of determination, from 0.65 to 0.79 for Nash–Sutcliffe coefficient and between −12.0 and − 30.2 for percentage bias. Spatial coverage of commercial farmland and built-up areas increased by 405 percent and 337 percent, respectively, while wetland and tropical high forests decreased 82 percent and 41 percent, respectively, during the period from 1995 to 2017. There is increased annual surface runoff (67 percent), sediment yield (109 percent), and water yield (72 percent) and decreased potential evapotranspiration (32 percent) and actual evapotranspiration (31 percent). Therefore, implementation of integrated basin management strategies such as soil and water conservation and afforestation could reverse the negative impacts and ensure effective water resources management. [ABSTRACT FROM AUTHOR]

Water‐related ecosystem services are the most expected benefits from ecological restoration worldwide, because they directly improve the quality of life of human populations around and downstream the restored areas. However, the poor comprehension of how the vegetation drives the hydrological processes has resulted in some major ecological disasters. Dib et al. (2023) tried to "shed light on the complex relationship between forest restoration and water‐related ecosystem services." However, while mentioning the decrease in water yield and highlighting the great benefits to water quality generally observed after forest restoration, they (1) overstated the contribution of planting forests to increase rainfall, and (2) omitted the substantial losses due to rain interception by the canopies when explaining the forest–water relationships. This reply aims to complement or rectify the arguments from Dib et al. (2023), clarifying some hydrological issues which are crucial for restoration planning and implementation. [ABSTRACT FROM AUTHOR]

The aim of this research is to assess the impact of future climate change on hydrological parameters (e.g., precipitation and temperature) in Ethiopia's upper Genale River basin. Future climate scenarios for the 2021–2050 and 2051–2080 periods were developed from four different GCM–RCM combinations of CORDEX-Africa projections using the Representative Concentration Pathways (RCP 4.5 and RCP 8.5). These climate models were bias corrected and used as input to the Soil and Water Assessment Tool (SWAT) model. During the 2030s (2021–2050) and 2060s (2051–2080), under the two RCPs, the projected precipitation in the annual and seasonal periods tends to decrease while temperatures increase. The simulated result revealed a significant change in hydrological components (e.g., During the 2060s), under the RCP4.5 scenario, CNRM-CM5 climate model runoff, ground water flow, and total water yield increased by 24.47%, 27.98%, and 28.56%, respectively. On the contrary, during the 2060s under the MIROC5 climate model, runoff, ground water flow, and total water yield reduced by 20.84%, 34.34%, and 25.8%, respectively. The annual hydrological components of the study area under MPI-ESM-LR, EC-EARTH, and MIROC5 showed a decrease in total water yield, surface runoff, ground waterflow, and lateral flow. However, due to a rise in temperature, evapotranspiration showed an increase up to 8.1% under all climate models (MPI-ESM-LR, EC-EARTH, CNRM-CM5, and MIROC5). The reduction in rainfall, which coincides with rising temperatures, is expected to reduce annual water yield, surface runoff, ground waterflow, and lateral flow by up to 39.8%, 39.3%, 50%, and 40.1%, respectively, across MPI-ESM-LR, EC-EARTH, and MIROC5 scenarios for the entire study basin in future projections. Our study helps to give a better insight into understanding climate change in watershed and can benefit the planning of water resources by strengthening adaptation strategies against the impacts of future climate change. [ABSTRACT FROM AUTHOR]

Hydrogeological, hydrochemical and isotopic traits of the groundwater in the Quaternary aquifer system in an urban-periurban locality within and encircling the Kolkata-Howrah twin city in the south Bengal Basin have been synthesised to explain the present- and paleo-hydrological processes, surface and groundwater interaction and mixing dynamics of contamination of groundwater. Rock-weathering, evaporation, ion-exchange and active mineral dissolution are the key processes commanding the groundwater chemistry. Freshwater flushing from the recharge zones had thinned the entrapped sea water which has generated the present-day brackish water by a non-uniform fusion. The best-fit line of the plots of δD and δ18O of groundwater samples displays a slope lower than that of local meteoric water line (LMWL) and global meteoric water line (GMWL) which hints that isotopic constitution of the groundwater of the present area is primarily formed by evaporation before or in the recharging process. A wide range of δ18O values in groundwater suggests that these waters are not blended enough to remove dissimilarities in isotope configuration of recharge water. This also suggests that many groundwaters are a result of mixing of present-day recharge and an older integrant recharged under previously cooler climatic conditions. The groundwater samples are more depleted of oxygen at the shallower level. The depleted samples cluster around the Tolly's nala (canal) where upper aquitard is missing or < 10-m thick. The tritium values range between 0.70 and 15.02 which indicate the occurrence of 'sub-modern', 'a mix of modern and sub-modern water' and 'modern water'. It indicates mingling of isotope-depleted water from the Hugli River by means of Tolly's canal with relatively less-depleted groundwater of Kolkata's late Pleistocene aquifer. The tritium values and Cl/Br ratio of groundwater samples adjoining Tolly's canal and elsewhere refer the direct infiltration of 'modern wastewater and freshwater' which mixes with the 'sub-modern water' in the aquifer system. [ABSTRACT FROM AUTHOR]

Study region: A gravel desert in the middle reaches of the Heihe River Basin, northwestern China. Study focus: Lack of long-term monitoring of soil water and groundwater level (GL) limited accurately quantifying the interactions between soil water, groundwater, and the shrubs in the desert ecosystems. This study focused on clarifying the water movement in the groundwater-soil-plant-atmosphere continuum in the desert ecosystems. Hydrological processes of a shrub community were simulated by developing the HYDRUS-1D model based on the twelve-years monitoring in a gravel desert. New hydrological insights for the region: Evapotranspiration of the shrub community was properly partitioned by the Penman-Monteith equation with the dual crop coefficient approach. Reaumuria songarica and Nitraria sphaerocarpa community relied on shallow soil water. Actual transpiration and evapotranspiration ranged from 33 mm and 80 mm in a dry year to 65 mm and 171 mm in a wet year, respectively. Only 39 % of evapotranspiration was used for shrub growth, and growing-season rainfall was more efficiently used in a dry year. Water rising from lower layers was dominant in the 0–10 m layer. The capillary fringe varied from 102 cm to 267 cm, averaging 205 cm above GL during the growing seasons. The rising groundwater is unavailable but promising for the shrubs’ utilization. The results of this study are valuable for developing sustainable management strategies for the similar gravel desert ecosystems.

The flows of surface water and groundwater from the Andes to the Atacama Desert are a vital source of freshwater, supporting ecosystems and human activities, but few substantive studies have addressed the hydrological and hydrogeological functioning of these systems. A dispute between Chile and Bolivia concerning the transboundary Silala River, recently heard before the International Court of Justice, The Hague, provided a unique opportunity for new scientific studies, reviewed in this Special Issue. First, findings from field studies that address the geological and geomorphological evolution of the Silala River basin and its current status, the key hydrological processes (including infiltration, actual evaporation from wetlands and alluvial plains, and surface water‐groundwater interactions), and the hydrogeological characterization of the major aquifers are reviewed. The dispute arose because Bolivia disagreed that the Silala was a transboundary river, subject to international law. As the Court proceedings evolved, this was accepted by Bolivia, but effects on surface flows of historical channelization in the Bolivian headwater wetlands remained a point of legal and technical disagreement. Bolivia asserted large increases in surface flow, based on modeling by their consultants, DHI. Chile held that these effects are small. In the second part of this paper, we summarize the modeling evidence. Chile's use of DHI's models, and its own hydrological and groundwater modeling of the basin, fully support Chile's position. We conclude with discussion of the Court's judgment, the challenges of physically‐based modeling of small changes in complex systems, and associated implications for judicial practice. This article is categorized under:Human Water > Water GovernanceScience of Water > Hydrological ProcessesScience of Water > Water and Environmental Change [ABSTRACT FROM AUTHOR]

The Silala River basin is located in a remote area in the Andes Mountain range, where hydro‐meteorological and hydrogeological data are scarce. Consequently, the hydrological functioning of this river system was not well understood. Due to a dispute between Chile and Bolivia over the status and use of the waters of the Silala River, Chile requested the International Court of Justice to adjudge the Silala River system to be an international watercourse. To support the case, scientific studies were carried out in both countries to fill hydrological and hydrogeological knowledge gaps. This article reviews the Silala River basin topographic characterization, historical water use, and the dominant hydrological processes, and briefly summarizes an enhanced monitoring programme, reported in more detail elsewhere in this Special Issue. The longitudinal topographic profile and river slope show that Silala fluvial system is an exorheic watershed; waters from the Cajones and Orientals wetlands in Bolivia, the two headwater sources of the Silala fluvial system, naturally flow from Bolivia to Chile, demonstrating that the Silala River system is indeed an international watercourse. New hydro‐meteorological, hydrological and hydrogeological measurement stations were installed in both countries and provided improved process insights and spatiotemporal coverage within the basin. These new observations helped to populate hydraulic, hydrological, and hydrogeological models, aimed to improve understanding of the functioning of the system, including the effects of historical disturbance due to channelization of the Bolivian wetlands. This article is categorized under:Science of Water > Hydrological ProcessesHuman Water > Rights to Water [ABSTRACT FROM AUTHOR]

This editorial introduces the Special Issue titled "Water Resources and Sustainable Development," underscoring the critical need for sustainable management of water resources in light of increasing demand, climate change impacts, and pollution. The issue delves into the intricate relationship between water availability, quality, utilization, and the socioeconomic determinants shaping these aspects, highlighting the necessity for novel, balanced strategies that cater to societal, economic, and environmental requirements. The research within this Special Issue is segmented into four key areas: understanding hydrochemical properties and water quality; evaluating anthropogenic effects on water resources; strategizing water resource management; and applying technological innovations in water resource management. Collectively, these studies broaden our comprehension of water resources and sustainable development, stressing the importance of continuous research in this sphere. As we look ahead, this editorial accentuates the importance of ongoing exploration and innovation in these pivotal areas, focusing on understanding climate change implications, mitigating human-induced impacts, refining water management strategies, and harnessing technological advancements. Its overarching aim is to propel worldwide initiatives towards achieving comprehensive water security and sustainability. [ABSTRACT FROM AUTHOR]

The enormous heterogeneity and complexity of landscape patterns and their linkage with the hydrological responses have rarely been quantified and cataloged, especially in ungauged regions. This research therefore linked the landscape characteristics to hydrological processes using a newly developed runoff landscape index (RLI) at the watershed scale in Ardabil Province, northwest Iran. First, 11 common landscape metrics were calculated using Fragstats 4.2.1 software. Then, a runoff landscape index (RLI) was developed based on land cover (λC), soil (λK), and topography (λS) factors in 28 watersheds. Correlation and regression analyses were also conducted to determine the relationship between RLI, commonly used landscape metrics, and mean base flow. The spatial variations of all meaningful landscape metrics and RLI were considerable throughout the study watersheds. The mean values of λC, λK, and λS were found to be 2.78 ± 1.08, 0.50 ± 0.10, and 1.22 ± 0.30, respectively. The mean RLI varied from 0.00009 in the Lay Watershed with an area of 19.09 km2 to 0.28 in the Boran Watershed with 10,268.95 km2. The correlation coefficient (r > 0.42; p-value < 0.05) was obtained significantly between RLI and only five landscape metrics, including the largest patch index (LPI), landscape shape index (LSI), landscape division index (DIVISION), splitting index (SPLIT), and Shannon's diversity index (SHDI). In addition, a regression model with R2 of 0.97 and 0.67, respectively, in calibration and validation steps was established between river base flow as the dependent variable and main waterway length, LPI, LSI, SPLIT, modified Simpson's diversity index (MSIDI), and λS as independent variables. The result confirms the significant interdependence of RLI and landscape characteristics, which can be used to interpret the landscape's dynamic and its effects on hydrological processes. [ABSTRACT FROM AUTHOR]

Climate change could add a variety of uncertainties to hydrological processes and water resources. Very limited efforts have been devoted to applying the US-EPA (Environmental Protection Agency)'s Hydrologic and Water Quality System (HAWQS) model for predicting climate change impacts on hydrological processes at the basin scale. Here, we applied the model to project the next 50 years' (from 2021 to 2070) hydrological processes at the Yazoo River basin in Mississippi, USA. Simulations showed that over the next 50 years, there are no significant trends in monthly precipitation, ET, runoff and discharge; only 2% of the annual precipitation percolated into the deep aquifer; and dry seasons become dryer and wet seasons become wetter. These findings provide very useful information to stakeholders for water resource management. Our study further suggests that the HAWQS model is a user-friendly and time-saving tool for basin-scale hydrological modelling. [ABSTRACT FROM AUTHOR]

Under the influence of mining activities, investigating hydrological processes is an important cornerstone of water resources and eco-environment protection. In this study, the spatio-temporal variations of stable isotopic compositions (δD and δ18O) of river water and groundwater in five periods of a hydrological year were analyzed to identify the origin and hydraulic connection of water bodies in the mining district under mining disturbance. The δD and δ18O indicate that the water bodies in the study area are mainly recharged by local precipitation and undergo evaporation. There is a close hydraulic connection between river water, mine water, and groundwater, and the deep confined water is affected by the river water and phreatic water due to the developing water-conducting fractures. The δ18O of phreatic water in each period is depleted in the southwest and enriched in the northeast of the study area. The δ18O of confined water has an obvious spatial variation in the wet season due to the combined effects of opencast working and underground mining, whereas uniform spatial variation is observed in the dry season. Compared with the dry season, mining disturbances have a greater impact on river water and groundwater in the wet season. The difference in spatial variation of δ18O between phreatic and confined water may be attributed to the easier recovery of phreatic water than confined water after mining disturbance. This finding provides important information about the hydrological characteristics of the Pingshuo mining district.

The Akaki River catchment is undergoing rapid urbanization and substantial deforestation, leading to a decline in its hydrological conditions. Investigating how changes in land use and land cover (LULC) affect the hydrological cycle in urbanized catchments like the Akaki River in the Awash Basin is a priority in natural resource utilization and management. By analyzing satellite images and using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) and Partial Least Square Regression (PLSR) models, this study examined the hydrological responses such as water yield (WY), sediment export (SE) and soil loss (SL) to the prevailing LULC changes in the catchments. The results showed an increasing trend of risks in surface runoff and sediment export from the catchments in the past three decades. The Analysis of Variance (ANOVA) test results showed significant variations in WY, SE, and SL across LULC types throughout the study period. The variables WY, SE, and SL increased by 35.25%, 8.11%, and 10.71%, respectively. The magnitude of change in SE, SL, and WY over the study period was substantially influenced by not only the change in LULC but also by the dynamics. Most importantly, settlements and farmlands were the main factors that influenced the hydrological components. These two LULC types attained greater variable importance for projection (VIP) and parameter weight (w) values of 1.31 and 0.61 for settlement and 1.19 and 0.56 for farmlands, respectively. The results of the study underlined the importance of regulating the rapidly changing LULC change and implementing conservation measures in order to attain a sustained hydrological and ecological balance in the Akaki River catchments,

Climate change is anticipated to have long-term effects on hydrological processes and patterns, leading to water stress in agroecological catchments. Climate change escalates water scarcity in the Usangu catchment, as evidenced by the drying up of rivers during the dry season. Therefore, this study was undertaken to assess climate change impacts on hydrology by utilizing the Soil Water Assessment Tool (SWAT) model and an ensemble mean of five Global Circulation Models (GCMs) under two shared socio-economic pathway (SSP) emission scenarios. Downscaling of GCMs was performed by the LARS-WG statistical downscaling tool. In comparison to the baseline period, short rain intervals are expected to occur between 2030 and 2060, with a mean annual precipitation increase of 7 and 17% in SSP 2–4.5 and SSP 5–8.5, respectively. Maximum and minimum temperatures are expected to rise by 0.6–2 °C. Corresponding to future temperature increases, evapotranspiration would increase to about 30% and decrease water yield and groundwater recharge by 7 and 26% in SSP 2–4.5 than in SSP 5–8.5. However, the effect of precipitation increase is shown by increased surface runoff and streamflow during wetter months. These findings provide watershed managers with crucial information for planning and managing the catchment in light of a changing climate. HIGHLIGHTS Climate change has a more severe impact on water-competitive catchments, particularly Usangu.; Increased precipitation would increase surface runoff more in lowland areas.; Usangu will experience shorter rain intervals as a result of climate change.; Temperature rise of 0.6–2 °C increases evapotranspiration in both scenarios.; Higher temperature in SSP 2–4.5 reduces water yield and recharge by 7 and 26% compared to SSP 5–8.5.;

Study Region: The Fenhe River Basin (FRB) is an important tributary of the Yellow River Basin and locate in a semi-arid and semi-humid region in northwest China. Over the past four decades, significant anthropogenic activities have resulted in significant land use and land cover change (LUCC) that have markedly impacted hydrological processes in FRB.Study Focus: To analyze land use changes under multiple historical land use scenarios from LU1980 to LU2015, and to establish the Water and Energy transfer Processes in Large basins (WEP-L) model to quantify the influences of LUCC on hydrological processes, particularly on baseflow.New hydrological insights for the region: LUCC from LU1980 to LU2015 resulted in a 14.5 % increase in water yield (WY) and a 2.7 % and 1.4 % decrease in baseflow (BF) and evapotranspiration, respectively. Urbanization led to a significant increase in WY and a reduction in BF, exhibiting strong spatial gradients between urban centers and their peripheries. Increases in forestland decreased WY, while ET showed no significant change due to large absolute values and moisture limitations. Furthermore, the response of BF to forest cover exhibits spatial variation. A negative correlation between BF and forest cover was evident in upstream, whereas no significant correlation was observed in downstream. The findings of this study offer valuable insights for land use planning and sustainable watershed management in semi-arid semi-humid region.

Study region: Mahanadi reservoir project complex (MRP), Chhattisgarh, India Study focus: This study assesses and compares the performance of the Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 models in modeling the hydrological regime. The study compared the performance of 13 CMIP6 GCMs in two Shared Socioeconomic Pathways (SSEPs) with that of 16 CMIP5 GCMs in two Representative Concentration Pathways (RCPs). Before being used to drive the Soil and Water Assessment Tool (SWAT) for streamflow prediction, the raw CMIP outputs were adjusted and downscaled using Bias Correction and Spatial Disaggregation methods (BCSD). In addition, the water deficits were also assessed between the mean monthly released by the optimized model and the mean monthly water demand. Results of this research projected the domestic water demand for future scenarios (2023–2099). New hydrological insights for the study region: The results of this study revealed that the genetic algorithm (GA) outperforms the various optimization techniques for CMIP5, with deficits observed by the GA algorithm. In addition, CCCmaCanESM2 was found to be the most efficient among CMIP5 GCMs, whereas MPI-ESM1–2-HR was used for CMIP6 GCMs. Overall, the CMIP6 multi-model mean ensemble (MMME) outperformed the CMIP5 MMME in simulating streamflow over the study area at annual and seasonal timescales. CMIP6 MMME also reduced maximum and minimum temperature biases over the study region significantly. In overall conclusion, the CMIP6 ensemble offers a lower margin of uncertainty for future climate projections and better credibility for hydrological effect analysis. The results further indicate that satisfactory steam flows can be obtained from the SWAT model while slight underestimations can be seen for higher discharges. In addition, the projected domestic water demand based on future population and irrigation demand clearly showcases significant annual increases.

Vegetation in natural desert hinterland oases is an important component of terrestrial ecosystems. Determining how desert vegetation responds to natural variability is critical for a better understanding of desertification processes and their future development. The aim of this study is to characterize the spatial distribution of vegetation in the natural desert hinterland and to reveal how different environmental factors affect vegetation changes. Taking a Taklamakan Desert hinterland oasis as our research object, we analyzed the effects of different environmental factors on desert vegetation using a time-series normalized difference vegetation index (NDVI) combined with meteorological, topographic, and hydrological data, including surface water and groundwater data. Vegetation was distributed in areas with high surface water frequency, shallow groundwater levels, relatively flat terrain, and dune basins. NDVI datasets show greening trends in oasis areas over the past 20 years. The frequency of surface water distribution influences water accessibility and effectiveness and shapes topography, thus affecting the spatial distribution pattern of vegetation. In this study, areas of high surface water frequency corresponded with vegetation distribution. The spatial distribution of groundwater depth supports the growth and development of vegetation, impacting the pattern of vegetation growth conditions. Vegetation is most widely distributed in areas where the groundwater burial depth is 3.5–4.5 m. This study provides data for restoring riparian vegetation, ecological water transfer, and sustainable development. [ABSTRACT FROM AUTHOR]

Hydrometeorological monitoring and continuous data collection in ungauged mountainous regions are exciting and challenging for water resource planners compared to the measurement in plain areas. Lesser Himalayas in the mountainous areas face the insufficiency of continuous hydrometeorological data, hindering our understanding of hydrological processes and hampering integrated water resources management. This present study focuses on the setup of the field instruments for collecting hydrometeorological data and analyzing continuously collected data at Aglar watershed to assess hydrometeorological parameters' spatial and temporal distribution. The instrumentation includes monitoring one sub-surface flow, five stream flows, four rain gauges, and one automatic weather station. The relationship between the stage and the discharge was established based on the collected data for three streams. The analyzed seasonal rainfall revealed 726.7 mm of rain occurred during the monsoon with an intensity of less than 16 mm/day. The Paligaad sub-watershed displayed a flashy response towards the rainfall events, whereas the Upper Aglar exhibited a wide range of dampening runoff responses for different rainfall events. The monitored sub-surface flow varies annually, and during the monsoon season, interflow and baseflow hydrograph decayed more rapidly at the rate of 0.04 day−1 and 0.78 day−1, respectively. The installed AWS has been used to measure crop water requirements and plan for better strategies to cope with future food and water security. The high-frequency generated data will help answer the queries related to hydrological responses of different watershed characteristics. [ABSTRACT FROM AUTHOR]

Accurate monthly streamflow prediction is crucial for effective flood mitigation and water resource management. The present study proposes an innovative similarity-derived model (SDM), developed based on the observation that similar monthly streamflow patterns recur across different years under comparable hydrological and climate conditions. The model is applied to the Lancang River Basin in China. The model performance is compared with the commonly used support vector machine (SVM) and Mean methods. Evaluation measures such as RMSE, MAPE, and NSE confirm that SDM6 with a reference period of six months achieves the best performance, improving the Mean model by 79.9 m3/s in RMSE, 6.07% in MAPE, and 8.62% in NSE, and the SVM by 53.65 m3/s, 0.24%, and 5.53%, respectively. [ABSTRACT FROM AUTHOR]

In recent years, many two‐dimensional (2D) hydrodynamic models have been extended to include the direct rainfall method (DRM). This allows their application as a hydrological‐hydrodynamic model for the determination of floodplains in one model system. In previous studies on DRM, the role of catchment hydrological processes (CaHyPro) and its interaction with the calibration process was not investigated in detail. In the present, case‐oriented study, the influence of the spatiotemporal distribution of the processes precipitation and runoff formation in combination with the 2D model HEC‐RAS is investigated. In a further step, a conceptual approach for event‐based interflow is integrated. The study is performed on the basis of a single storm event in a small rural catchment (low mountain range, 38 km2) in Hesse (Germany). The model results are evaluated against six quality criteria and compared to a simplified baseline model. Finally, the calibrated improved model is contrasted with a calibrated baseline model. The results show the enhancement of the model results due to the integration of the CaHyPro and highlight its interplay with the calibrated model parameters. [ABSTRACT FROM AUTHOR]

Abstract In recent years, many two‐dimensional (2D) hydrodynamic models have been extended to include the direct rainfall method (DRM). This allows their application as a hydrological‐hydrodynamic model for the determination of floodplains in one model system. In previous studies on DRM, the role of catchment hydrological processes (CaHyPro) and its interaction with the calibration process was not investigated in detail. In the present, case‐oriented study, the influence of the spatiotemporal distribution of the processes precipitation and runoff formation in combination with the 2D model HEC‐RAS is investigated. In a further step, a conceptual approach for event‐based interflow is integrated. The study is performed on the basis of a single storm event in a small rural catchment (low mountain range, 38 km2) in Hesse (Germany). The model results are evaluated against six quality criteria and compared to a simplified baseline model. Finally, the calibrated improved model is contrasted with a calibrated baseline model. The results show the enhancement of the model results due to the integration of the CaHyPro and highlight its interplay with the calibrated model parameters.

Inappropriate vegetation reconstruction in the Loess Plateau region has led to a significant increase in regional evapotranspiration and water consumption, further aggravating the shortage of soil water resources in the Loess Plateau region. The Jing River basin is a typical area for vegetation reconstruction in the Loess Plateau region. A thorough understanding of changes in hydrological processes in the Jing River basin is of significant scientific importance for efficient utilization of soil water resources and sustainable vegetation restoration in the region. In this study, the physically based Water and Energy Transfer Processes (WEP) distributed hydrological model was used to simulate key hydrological processes in the Jing River Basin during different periods before and after the implementation of cropland conversion to forest and grassland from 1980 to 2019. The results showed that after the implementation of cropland conversion to forest and grassland from 2000 to 2019, the average runoff volume in the Jing River Basin decreased by 20.91%. The most significant decrease in average runoff occurred in the central and northern parts of the basin, with a maximum reduction of 48.6%. The decrease in runoff in flood season is more obvious. The peak discharge decreased by 24.91%, and the most significant decrease occurred in the northern and central parts of the basin, ranging from 10.3% to 50.2%. The spatial distribution pattern of average soil moisture in the 0–0.8 m soil layer showed more moisture in the south and less in the north, with the minimum value occurring in certain areas in the eastern part of the basin. Overall, the implementation of cropland conversion to forest and grassland led to a certain degree of decrease in soil moisture in the basin. After the implementation of cropland conversion to forest and grassland, reference evapotranspiration fluctuated only in specific areas of the basin with no significant overall change. [ABSTRACT FROM AUTHOR]

The characteristics of dynamic and delayed channel geomorphic responses to changing hydrological processes are still insufficiently understood, especially in large dammed rivers and segments farther downstream from the dam. Geomorphic effects farther downstream from the dam could be easily underestimated. This study investigated the hydrological changes and channel adjustments in the Chenglingji–Jiujiang Reach (CJR), ~450 km downstream from the Three Gorges Dam. The post‐dam evolution developed from early low‐intensity alternating erosion/deposition to later intense erosion. This is because the increasing sediment starvation caused by the dam and attenuated upstream sediment replenishment produced streams with excess transport capacity for the farther downstream channel, where the early mild evolution and fine‐sandy riverbed guaranteed adequate sediment availability. Additionally, the increasing geomorphic contribution of low‐to‐medium flows, coupled with revetment resistance to lateral adjustments, promoted migration of the major adjustment area from above the bankfull channel to below the medium‐flow channel and characterized erosion by one‐way incision with no evident channel narrowing/widening. The net increase in reach‐averaged thalweg incision depth during a later period (2.85 m) was 35 times larger than that during an earlier period (0.08 m). Channel morphogenetic intra‐annual hydrological processes were identified to contain all discharges smaller than 39 000 m3/s, and discharges of 30 000–39 000 m3/s exerted maximum geomorphic effects. On this basis, a method for estimating the cumulative erosion volume at equilibrium was proposed and integrated into the Delayed Response Model. The encouraging simulation and prediction results indicate that geomorphological adjustments within the CJR were greatly influenced by the hydrological conditions of current year and previous 4 years, while the impacts of extreme and rare events depended more on the consistency of their hydrological behaviours with channel evolutionary trends than on their temporal distances. This work facilitates the understanding and prediction of channel self‐adjustments farther downstream from the dam. [ABSTRACT FROM AUTHOR]

Estimation of hydrological processes is critical to water resource management, water supply planning, ecological protection, and climate change impact assessment. Mountains in Central Asia are the major source of water for rivers and agricultural practices. The disturbance of mountain forests in the region has altered the hydrological processes and accelerated soil erosion, mudflow, landslides, and flooding. We used the SWAT (Soil and Water Assessment Tool) model calibrated and validated with remote sensing data to quantify the mountainous hydrological processes in the Aktash River watershed (ARW) of Uzbekistan, Central Asia. Simulations showed that the daily surface runoff and streamflow closely responded to daily precipitation. Groundwater discharge reached its maximum in winter because of snowmelt. The wet months were from July to December, and the dry months were from January to June. The magnitudes of the seasonal hydrological processes were in the following order: fall > summer > winter > spring for precipitation and surface runoff; summer > spring > fall > winter for evapotranspiration (ET); winter > spring > fall > summer for snowmelt; fall > winter > summer > spring for water yield and streamflow; and winter > fall > spring > summer for groundwater discharge. The Mann–Kendall statistical test revealed a significant increasing trend for the annual precipitation (τ = 0.45, p < 0.01) and surface runoff (τ = 0.41, p < 0.02) over the past 17 years from 2003 to 2019. Compared to rangeland, forested land decreased monthly and annual average surface runoff by 20%, and increased monthly and annual average groundwater recharge by about 5%. Agricultural land had much higher unit-area values (mm/km2/y) of ET, groundwater recharge, and water yield than those of urban, forest, and range lands. Our research findings provide useful information to farmers, foresters, and decision makers for better water resource management in the ARW, Central Asia, and other mountain watersheds with similar conditions. [ABSTRACT FROM AUTHOR]

The need to increase understanding of the impacts of changing natural and anthropogenic drivers on hydrological processes on local and regional scales is an essential prerequisite for advancing hydrology and a precondition for solving water resources management tasks. Slovakia exhibits abundant spatial and temporal variability of hydrological processes complicating the generalisation of runoff regimes. Changing climate and recent extreme floods and droughts put additional pressure on improving the observing, monitoring, describing, and modelling of hydrological processes. This paper reviews the response of hydrologic research in Slovakia to these challenges published in international journals from 2019 to 2022. It continues the practice of publishing the review part of the Slovak National Reports to IUGG on behalf of the IAHS (Szolgay, 2003; 2007; 2011; 2015; 2019), which follows the custom of National IUGG Committees to prepare a Quadrennial Report for the IUGG General Assemblies containing comprehensive summaries of national activities in geodesy and geophysics (Szolgay, et al., 2023). [ABSTRACT FROM AUTHOR]

The role of aquifers in extreme hydrological events has been highlighted in numerous different contexts, both for river high flows and low flows. Many aquifers are monitored by networks of piezometers that measure groundwater levels: their long-term records allow for a joint analysis of contemporaneous streamflow time series. Yet, groundwater level data are rarely used in surface hydrological modelling approaches, because of the huge complexity of river–aquifer interactions. We propose a simple correlation analysis between yearly extrema of groundwater level and streamflow time series, performed on a large set of 107 catchments and 355 piezometers, located throughout mainland France. We show that it is possible to discriminate between aquifers that correlate only with high-flow events, only with low flows, with both types of events or with none of them. Our typology presents new opportunities to characterise the surface–groundwater exchanges, which can be very important for understanding the occurrence of river extremes.

The last decade has seen considerable progress in scientific research on vegetation ecosystem services. While much research has focused on forests and wetlands, grasslands also provide a variety of different provisioning, supporting, cultural, and regulating services. With recent advances in remote sensing technology, there is a possibility that Earth observation data could contribute extensively to research on grassland ecosystem services. This study conducted a systematic review on progress, emerging gaps, and opportunities on the application of remote sensing technologies in quantifying all grassland ecosystem services including those that are related to water. The contribution of biomass, Leaf Area Index (LAI), and Canopy Storage Capacity (CSC) as water-related ecosystem services derived from grasslands was explored. Two hundred and twenty-two peer-reviewed articles from Web of Science, Scopus, and Institute of Electrical and Electronics Engineers were analyzed. About 39% of the studies were conducted in Asia with most of the contributions coming from China while a few studies were from the global south regions such as Southern Africa. Overall, forage provision, climate regulation, and primary production were the most researched grassland ecosystem services in the context of Earth observation data applications. About 39 Earth observation sensors were used in the literature to map grassland ecosystem services and MODIS had the highest utilization frequency. The most widely used vegetation indices for mapping general grassland ecosystem services in literature included the red and near-infrared sections of the electromagnetic spectrum. Remote sensing algorithms used within the retrieved literature include process-based models, machine learning algorithms, and multivariate techniques. For water-related grassland ecosystem services, biomass, CSC, and LAI were the most prominent proxies characterized by remotely sensed data for understanding evapotranspiration, infiltration, run-off, soil water availability, groundwater restoration and surface water balance. An understanding of such hydrological processes is crucial in providing insights on water redistribution and balance within grassland ecosystems which is important for water management.

【Objective】 The Bayin river basin is located in Qinghai province; the physical and chemical properties of its water vary with many factors. In this paper, we analyze the hydro-chemical properties and hydrogen and oxygen isotopes in different reaches of the basin. 【Method】 Water samples were taken from different locations in the basin, and the hydrochemical property and stable isotopes in each sample were analyzed using standard laboratory methods. 【Result】 ①The average pH, TDS and DO of the water samples are 7.53, 399 mg/L and 5.46 mg/L respectively. The predominant anion in the surface water and groundwater is SO42- and Cl-, respectively, while the main cation in the waters is Ca2+, in spring. ②The Na+/(Na++Ca2+) ratio is distributed mainly between the evaporation crystallization zone and the rock weathering zone, far away from the atmospheric precipitation zone. ③The slope of the water evaporation line is 4.94, significantly lower than that of local and global atmospheric precipitation lines. The average stable hydrogen and oxygen isotopes in the river water are between the average atmospheric precipitation and the groundwater in the mountainous region in north of the basin. ④Evaporation crystallization and rock weathering are the main factors controlling hydro-chemical property of the basin water, and rock weathering and dissolution of evaporite and carbonate are the main sources of the ions. ⑤Recharge to the upstream groundwater is surface water leakage and lateral runoff, accounting for 43.36% and 56.64% of the total recharge, respectively, while recharge to the groundwater in the middle reach is surface water and upstream river water, accounting for 69.51% and 30.49% of the toral recharge, respectively. In the downstream reach, groundwater recharges the river and spring, accounting for 10.26% and 89.74% of their total recharges, respectively.

This paper presents the background, scientific objectives, experimental design, and preliminary achievements of the Xin’anjiang nested experimental watershed (XAJ-NEW), implemented in 2017 in eastern China, which has a subtropical humid monsoon climate and a total area of 2674 km2. The scientific objectives of the XAJ-NEW include building a comprehensive, multiscale, and nested hydrometeorological monitoring and experimental program, strengthening the observation of the water cycle, discovering the spatiotemporal scaling effects of hydrological processes, and revealing the mechanisms controlling runoff generation and partitioning in a typical humid, hilly area. After two years of operation, preliminary results indicated scale-dependent variability in key hydrometeorological processes and variables such as precipitation, runoff, groundwater, and soil moisture. The effects of canopy interception and runoff partitioning between the surface and subsurface were also identified. Continuous operation of this program can further reveal the mechanisms controlling runoff generation and partitioning, discover the spatiotemporal scaling effects of hydrological processes, and understand the impacts of climate change on hydrological processes. These findings provide new insights into understanding multiscale hydrological processes and their responses to meteorological forcings, improving model parameterization schemes, and enhancing weather and climate forecast skills.

Karst wetland is an important regulator of karst ecosystems in southwest China and is of great significance to the sustainable development of the region. Water cycle, as the core factor to maintain the healthy operation of karst wetlands, has become a hot topic in current researches. Based on the field monitoring data of the Shizhiyan underground river system in the Guilin Huixian Wetland from April 15, 2020 to May 30, 2020, hydrological dynamic analysis and water balance are used to study the water cycle of the underground river system. The results show that (1) surface runoff, soil water, surface karst zone water and karst groundwater are sensitive to atmospheric rainfall, but the sensitivity degree is different. The sensitivity of karst groundwater is the highest, the sensitivity of surface runoff and surface karst zone water is weak, and the sensitivity of soil water is greatly affected by depth. (2) The proportion of all kinds of water circulation in the underground river system is different at different grades of rainfall, and the proportion of soil water in the system is the largest in light rain (24 h cumulative rainfall ranges from 4.2 mm to 10 mm), which accounts for about 75.87%. The proportion of soil water and karst groundwater in moderate rain (24 h cumulative rainfall is 17.8 mm) is the largest, which is about 43.38% and 44.12%, respectively. The proportion of karst groundwater in heavy rain (24 h cumulative rainfall is 24 mm) and heavy rainstorm (24 h cumulative rainfall ranges from 110.8 mm to 128.2 mm) is the largest, accounting for about 66.48%. (3) The average coefficient of regulation and storage in the study area is about 0.53, which is significantly higher than that of other karst areas, showing strong regulation and storage capacity. With the increasing rainfall, the coefficient of regulation and storage gradually decreases. (4) The conceptual model of water cycle of underground river system includes the transformation relationship and transformation amount among atmospheric rainfall, surface runoff, soil water, surface karst zone water and karst groundwater. The establishment of the conceptual model can provide a theoretical basis for the development and utilization of water resources and wetland protection of karst wetland.