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Background: Urban ecological health is crucial for the long-term sustainable development of watershed. Accurately evaluating the health level of the ecological environment helps to develop reasonable strategies for ecological environment restoration and resource management. This paper constructed a comprehensive evaluation index system based on the Pressure-State-Response (PSR) framework and evaluated the ecological health of eleven administrative regions in the Wei River Basin (WRB), northwest China in 1980, 2000, and 2020 using an evaluation model established by fuzzy mathematics. Further, obstacle degrees were used to quantify the contribution of pressure, state, and response modules, as well as individual indicators to ecological health. Results: The comprehensive evaluation system constructed based on the PSR framework could effectively reflect the ecological health conditions of different regions in the WRB. During the study period, the ecological health went through a process of first deterioration and then improvement. By 2020, the ecological health of seven administrative regions reached healthy levels. The state module was the main obstacle module of the PSR framework to the ecological health of the most regions. The population density (P1), patch density of construction land (S5), comprehensive elasticity index (S8), soil erosion index (R1), and per capital GDP (R3) were the most crucial individual indicators affecting the ecological health. For different cities, the main obstacle factors varied. In economically developed cities, the limiting effect of P1 was more significant, while in economically underdeveloped cities, the limiting effect of R3 was stronger. Conclusions: In response to the special natural environment and socio-economic conditions of arid and semi-arid areas in the WRB, an ecological health evaluation index system suitable for the characteristics of the basin was constructed. The results indicated that, to improve the levels of urban ecological health, it is necessary to restore the natural ecological environment and control population size while accelerating economic construction. Our results can provide scientific support for the ecological health evaluation and protection of the WRB and even the arid and semi-arid areas in northwest China. [ABSTRACT FROM AUTHOR]

Climate change and human activities exert significant influence on the water–sediment relationship in arid and semi-arid regions. Therefore, comprehending the underlying mechanisms is crucial for the effective management of water and soil resources, as well as integrated watershed management. This research focuses on the Kuye River watershed (KYH_W) in the middle reaches of the Yellow River in China, along with its sub-watersheds Wangdaohengtazi (WDHT_SW) and Xinmiaosi (XM_SW). This paper utilizes the Mann–Kendall non-parametric test and the double cumulative curve method to examine the interannual trends of runoff, sediment transport, precipitation, temperature, and NDVI factors. Furthermore, the method of the slope change ratio of cumulative quantity (SCRCQ) is utilized to quantitatively evaluate the impacts and contribution rates of climate change and human activities on water–sediment changes within each watershed. The results are as follows: (1) From 1969 to 2019, the entire watershed experienced a significant decrease in both runoff and sediment transport, with 1997 marking the year of abrupt change. However, following 2012, the KYH_W and WDHT_SW exhibited a noticeable rebound in runoff. (2) Human activities predominantly contribute to the reduction in water and sediment in the watershed. (3) After the abrupt change, between 1998 and 2011, the contribution rates of climate change and human activities to the annual runoff reduction in the entire KYH_W reached 33% and 64%, respectively. Moreover, these rates for sediment transport reduction reached 26% and 74%, respectively. Subsequently, after 2012, the contribution rates of both factors to the increase in watershed runoff reached 29% and 71%, respectively. Factors other than the NDVI, within human activities, played a dominant role in augmenting the watershed's runoff. (4) Prior to 2011, changes in vegetation cover resulting from the Grain for Green Program, as measured by the NDVI, emerged as the primary factor responsible for reduced runoff in the watershed. Conversely, factors other than the NDVI assumed dominance in reducing sediment transport. The SCRCQ method offers a quantitative approach to assessing water–sediment changes. Based on this method, the study further underscores the substantial impacts of climate change and human activities on variations in runoff and sediment transport within the KYH_W in the middle reaches of the Yellow River. Notably, the water–sediment changes in the KYH_W exhibit distinct stage-wise and spatial discrepancies, which warrant increased attention in future research endeavors. [ABSTRACT FROM AUTHOR]

Rivers are important carriers of water transmission, water supply, and water nourishment, and the virtuous cycle of their ecosystems is directly related to the degree of completion of the construction of ecological civilization and the high-quality development of the national economy. From the perspective of symbiosis theory, this paper constructs a river health value assessment index system and analyzes the symbiotic synergistic effect of nine provinces in the Yellow River Basin in China from 2000 to 2020 by using a logistic symbiosis evolution model. Health values at the Yellow River Basin scale and the provincial administrative area scale were also analyzed, and it was found that (1) the Yellow River Basin experienced a period of sub-par river health in the past, but with the implementation of ecological protection and high-quality development strategy in recent years, the health of the river showed an trend of improvement during the period of 2017–2020; (2) at the provincial administrative scale, the Yellow River Basin has significant differences, which are manifested in the obvious differences between provinces in terms of the functional value of river health provision and the economic functional value. In order to reduce the regional differences, it is recommended that the provinces work together and give full play to their own characteristics and strengths in the management of the watershed, so as to make up for the weaknesses of regional development and realize the synergistic development of the watershed; and (3) in terms of symbiosis level, rivers in the Yellow River Basin generally show parasitic relationships, and most of them exhibit natural ecological diversity and competitiveness with socio-economics. Therefore, a more comprehensive consideration of the balanced development of each function is needed in river health management in the future to achieve integrated watershed health. These results suggest that the development of river ecological health in the Yellow River Basin requires the joint efforts of the whole of society as well as regional synergy and integrated management at the policy level to achieve more sustainable and balanced watershed development. [ABSTRACT FROM AUTHOR]

Water-related cultural heritage architecture (WRCHA) represents a globally significant and potentially hybrid heritage found across river basins worldwide. Its spatial and temporal evolution characteristics offer insight into the development trends of river basin environments, yet their value within water-related cultural and environmental systems remain incompletely assessed. This study undertakes qualitative and quantitative analyses of the historical spatial and temporal distributions, influencing factors, and environmental changes affecting the water-related culture, climate, population, and urban areas of 295 WRCHA sites in the Li River Basin of China, employing drought–flood indices, GIS analyses, random forest algorithms, and other methodologies. The results reveal that (1) the Lishui Basin contains a significant distribution pattern of agglomeration for WRCHA within the river basin, concentrated along the river, at low altitudes, with minimal terrain variation, and radiating around ancient governance centers, with varying increases observed across different periods and aggregation zones and with significant spatial and temporal heterogeneities; (2) the distribution pattern is influenced by joint natural and human factors, closely tied to variables such as the river network density, DEM, population changes, and distance to ancient government sites; (3) the combination of the architecture's location and elevation, along with drought–flood curves, reflects the position of the ancient riverbed of the Lishui River and its historical maximum water level. The quantity of new constructions, in conjunction with the distance from ancient government centers and the trends in population change, thus indicates the urban scale and the frequency and severity of disasters. This study provides a research paradigm and historical reference model for investigating environmental changes in watershed systems, aiding in clarifying the historical human–water symbiosis pattern in the middle reaches of the Yangtze River. Such insights will furnish a scientific basis for future regional ecological planning and watershed environmental management. [ABSTRACT FROM AUTHOR]

Rice terraces are crucial for agriculture in China's southern mountainous regions. Land use and land cover change (LUCC) in these areas impact hydrology, but our understanding is limited. In this study, we applied the hydrological assessment tool SWAT to a selected small watershed in the rice terrace-dense area of central Hunan province, China. This study covered four LUCC periods over the past 40 years and was simulated at annual and monthly scales. The results showed that from 1980 to 2020, the areas of paddy fields and drylands decreased by 4.19% and 5.76%, respectively, while the areas of forests and construction land increased by 1.14% and 92.48%, respectively. During the past period, LUCC led to a decrease of 1.77% and 2.49% in runoff and infiltration, respectively, and an increase of 1.03% in ET. However, the water yield remained almost unchanged, indicating that the rice terrace plays a positive role in maintaining stable watershed water yield under LUCC. The results of the sub-basin analysis indicated that the transformation of paddy fields and forests directly determines the trend of hydrological changes. Land use type had the most significant impact on the runoff of the rice-terrace watershed, with the proportions of paddy fields and forests being the most influential factors. Paddy fields significantly influenced the stability of runoff at the watershed scale, suggesting that a high paddy field ratio doesn't ensure sustainability. This study offers valuable insights for managing small watershed terraces, land use planning, and achieving sustainable development in the watershed. [ABSTRACT FROM AUTHOR]

In conjunction with socioeconomic development in watersheds, increasingly challenging problems, such as scarcity of water resources and environmental deterioration, have arisen. Watershed management is a useful tool for dealing with these issues and maintaining sustainable development at the watershed scale. The complex and uncertain characteristics of watershed systems have a great impact on decisions about countermeasures and other techniques that will be applied in the future. An optimization method based on scenario analysis is proposed in this paper as a means of handling watershed management under uncertainty. This method integrates system analysis, forecast methods, and scenario analysis, as well as the contributions of stakeholders and experts, into a comprehensive framework. The proposed method comprises four steps: system analyses, a listing of potential engineering techniques and countermeasures, scenario analyses, and the optimal selection of countermeasures and engineering techniques. The proposed method was applied to the case of the Lake Qionghai watershed in southwestern China, and the results are reported in this paper. This case study demonstrates that the proposed method can be used to deal efficiently with uncertainties at the watershed level. Moreover, this method takes into consideration the interests of different groups, which is crucial for successful watershed management. In particular, social, economic, environmental, and resource systems are all considered in order to improve the applicability of the method. In short, the optimization method based on scenario analysis proposed here is a valuable tool for watershed management. [ABSTRACT FROM AUTHOR]

Model simulation plays a significant role in the water resources cycle, and the simulation accuracy of models is the key to predicting regional water resources. In this research, the Qianhe tributary at the Weihe River basin in Western China was selected as the study area. The tributary was divided into 29 sub-basins and 308 hydrological response units according to the spatial raster data and attribute data of the hydrology, meteorology, topography, land use, and soil types. On this basis, a soil and water assessment tool (SWAT) model for runoff simulation and evaluation of this region was established. A sensitivity test and parameter calibration were then executed on 15 parameters involved with surface runoff, soil flow, and shallow underground runoff. The simulation results demonstrate a calibration and verification error of 3.06–10.08%, with very small uncertainties throughout the simulation, whereas they exhibit relatively large errors in the simulation of the dry period (winter) but, in contrast, quite small errors in the rainy period (summer). In addition, the simulated runoff with a low value is overestimated. When the annual, monthly, and daily runoff are 4–13.5 m3/s, 4–69.8 m3/s, and 40–189.3 m3/s, respectively, the relative error is smaller, and the simulation results are more accurate. The sensitive parameters predominantly affecting the runoff simulation of the basin include soil evaporation compensation, runoff curve coefficient, vegetation transpiration compensation, and saturated hydraulic conductivity in this region. In the case of hypothetical land use change scenarios, we observe a great reduction in simulated runoff in arable land, woodland, and grassland, while we observe an increment in construction and residential land and wasteland. The annual and monthly runoff are increased by above 54.5%. With the increase in cultivated land and forestland, the annual and monthly runoff decrease by 24.6% and 6.8%, respectively. In the case of hypothetical scenarios under 24 climate combinations, if the precipitation remains unchanged, the increase and decrease in temperature by 1 °C leads to a decline and increment of runoff by −0.72% and 5.91%, respectively. With regard to the simulation for the future under the RCP2.6 and RCP8.5 climate scenarios, downscaling was employed to predict the runoff trend of the future. In short, this study provides a method for runoff inversion and water resources prediction in small mountainous watersheds lacking hydrological and meteorological observation stations. [ABSTRACT FROM AUTHOR]

Under the framework of payment for transboundary watershed ecosystem services (ESs), identifying midstream and downstream residents' preference and willingness to pay (WTP) for ESs provided by the upstream is crucial for sustainable watershed management. The residents' preferences and WTP are not evenly distributed within the watershed. This study uses a choice experiment assessing the spatial impact of physical distance (including residents' watershed location and distance to waterbody) and psychological distance on residents' preference and WTP for the Wei River Basin ESs. The results showed that midstream and downstream residents' preference and WTP for the ecological attributes have a significant distance-decay effect, either the physical distance to the upstream exit or physical and psychological distance to the waterbody. However, compared with the residents in the midstream, the residents downstream have a stronger preference and WTP for upstream ecological governance. Besides, the distance-decay effect differs between urban and rural residents. There is a psychological distance-decay effect in rural residents' preference for water quality and a physical distance-decay effect in their preference for water quantity, entertainment area, and cost; there is a physical distance decay effect in urban residents' preference for entertainment areas. The above differences lead to heterogeneity in WTP and total economic value (TEV) for ESs. When calculating the TEV of the transboundary watershed ES and charging the public, policymakers should consider the location of the residents, the physical and psychological distance to the water body, and the difference between urban and rural areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • We quantified the impacts of land use changes and dam construction on flood regulation service (FRS). • A transfer matrix of ecosystem FRS was developed associating with land use changes. • Both the amount and direction of land use changes play key roles in influencing the ecosystem FRS. • Land use outweighted dams in forming the annual FRS supplies. • Increases in FRS supply came more from dam construction (84.65%) than land use changes (15.35%). Flood regulation service (FRS) is essential for a sustainable landscape and human society. It is not only subject to land use changes, but also affected by engineered measures (e.g., dam construction). However, the comprehensive impacts of the two major driving factors are still to be elucidated. To fill the research gap, this paper aims to evaluate the response of basin-scale FRS supply and demand to land use changes and dam construction. A case study in the Yangtze River Basin, China, shows that the 2020 FRS supply is mainly from land uses (84.85%) rather than dams (15.15%), with the biggest contributions from water bodies (rivers and lakes, 30.00%) and forests (29.35%). Between 1980 and 2020, the total FRS supply has increased by 10.50%, from 1.48 × 1010 m3 to 1.64 × 1010 m3. The net increase mainly comes from dam construction (84.65%) rather than land use changes (15.35%). Regarding the land use changes, the developed transfer matrix shows the ecosystem FRS flows and indicates that both the land use change amount and direction play a key role, e.g., the declines in farmlands have increased ecosystem FRS supplies when transiting into forest lands (by 3.68 × 108 m3) and water bodies (by 1.37 × 109 m3), while have decreased the ecosystem FRS supplies by −1.96 × 107 m3 with the transition into construction lands. These findings could shed light on the divergent roles between land-based measures and engineered measures in managing flood risk. [ABSTRACT FROM AUTHOR]

Watershed eco-compensation (WEC) is considered a significant environmental policy instrument for watershed ecological protection and management. However, in the legislation and practice of eco-compensation in China, the development of the WEC mechanism is still in the initial stages. In this paper, the institutional opportunities and challenges of WEC are analyzed from the existing policies, laws, and economical instruments. Theoretically, WEC in China has seen a combination of punitive-based "Watershed Ecological Damage Compensation (WEDC)" and incentive-based "Watershed Ecological Protective Compensation (WEPC)". Through a comparative analysis of domestic and foreign watershed compensation practices, the results demonstrate that most of China's WEC projects have an insufficient legal basis, a single compensatory subject, insufficient compensation funds, and an imperfect market-oriented compensation mechanism. To improve watershed eco-compensation in China, it is recommended to strengthen legislation, select diversified eco-compensation approaches, and establish a market-based and systematic eco-compensation mechanism for watersheds. [ABSTRACT FROM AUTHOR]

As global warming produces dramatic climate changes, water management is facing increasingly serious challenges. Given to the process of climate change and its complex effects on watershed hydrology, this paper investigates the spatial and temporal variation characteristics of major climatic factors (i.e., precipitation and temperature) over the upper Yangtze River basin (UYRB), China. The statistical analyses are based on annual and seasonal scales during 1951–2020 with a recorded period of seven decades. The Mann–Kendall nonparametric test and R/S analysis are used to record the temporal trends (past and future) of climate variables; the Pettitt test, standard normal homogeneity test and Buishand test are used to detect the homogeneity in climate series. The sensitivities of the streamflow to climatic parameters are assessed at the watershed scale, especially considering the Three Gorges Dam's (TGD) effect on changing runoff. The results of the study indicate that the annual precipitation of 29 out of 34 series indicate homogeneity, while 31 out of 34 annual mean temperature series show heterogeneity, with jump points around 1997 in the mean temperature of 20 sites. Detectable changes in precipitation were not observed during 1951–2020; however, the temperature increased significantly in the whole basin on annual and seasonal scales, except for several stations in the eastern part. The magnitude of increase in air temperature in high altitudes (Tibet Plateau) is higher than that in low altitudes (Sichuan Plain) over the last seven decades, and future temperatures continue to sharply increase in high altitudes. The TGD plays an important role in explaining the seasonal variations in streamflow at Yichang station, with streamflow experiencing a sharp increase in winter and spring (dry season) and a decrease in summer and autumn (rainy season) compared to the pre-TGD period. The streamflow variation at an annual scale is mainly regulated by climate fluctuation (variation in precipitation). During the last seven decades, increasing air temperature and decreases in rainfall and runoff signify reduced water resources availability, and the climate tends to be warmer and drier over the basin. The sensitivity of the streamflow to watershed precipitation is higher than that to temperature, with variation in annual rainfall explaining 71% of annual runoff variability. [ABSTRACT FROM AUTHOR]

Large dams represent a whole complex of social, economic and ecological processes, perhaps more than any other large infrastructure project. Today, countries with rapidly developing economies are constructing new dams to provide energy and flood control to growing populations in riparian and distant urban communities. If the system is lacking institutional capacity to absorb these physical and institutional changes there is potential for conflict, thereby threatening human security. In this paper, we propose analyzing sustainability (political, socioeconomic, and ecological) in terms of resilience versus vulnerability, framed within the spatial abstraction of a powershed. The powershed framework facilitates multi-scalar and transboundary analysis while remaining focused on the questions of resilience and vulnerability relating to hydropower dams. Focusing on examples from China, this paper describes the complex nature of dams using the sustainability and powershed frameworks. We then analyze the roles of institutions in China to understand the relationships between power, human security and the socio-ecological system. To inform the study of conflicts over dams China is a particularly useful case study because we can examine what happens at the international, national and local scales. The powershed perspective allows us to examine resilience and vulnerability across political boundaries from a dynamic, process-defined analytical scale while remaining focused on a host of questions relating to hydro-development that invoke drivers and impacts on national and sub-national scales. The ability to disaggregate the affects of hydropower dam construction from political boundaries allows for a deeper analysis of resilience and vulnerability. From our analysis we find that reforms in China's hydropower sector since 1996 have been motivated by the need to create stability at the national scale rather than resilient solutions to China's growing demand for energy and water resource control at the local and international scales. Some measures that improved economic development through the market economy and a combination of dam construction and institutional reform may indeed improve hydro-political resilience at a single scale. However, if China does address large-scale hydropower construction's potential to create multi-scale geopolitical tensions, they may be vulnerable to conflict – though not necessarily violent – in domestic and international political arenas. We conclude with a look toward a resilient basin institution for the Nu/Salween River, the site of a proposed large-scale hydropower development effort in China and Myanmar. [Copyright &y& Elsevier]

China's seven major basins cover 45.3% of the total area of this country, where 1.2 billion people are living in. Water quality of these basins is vital for China's water security and sustainable development. This paper presents a methodology for assessing the surface water quality and long-term trends of the seven major basins based on water quality identification index, a method to sort the pollution levels of both the same and different water quality parameters from a quantitative perspective. Water quality identification indices of dissolved oxygen, permanganate index, and ammonia nitrogen and overall water quality identification indices for the weekly data over the period of 2004–2018 were calculated. A big data analysis was then performed to probe how the water quality changed, including long-term water quality improvement over the 15 years, weekly water quality change throughout the year and water quality association among different basins. The study shows that significant improvement in water quality has occurred in China's seven major rivers over the past 15 years as a result of the construction of sewage treatment infrastructures. It also reveals obviously weekly water quality change for dissolved oxygen and ammonia nitrogen, and spatial heterogeneity of water quality between China's southern rivers and northern rivers, due to the drive of natural and anthropogenic factors such as water temperature, runoff flow and non-point source pollution input. In the future, efforts still need to be made regarding the perfection of urban sewer network and non-point source pollution control, so as to further improve the water quality of these basins. • Water quality identification index was used to assess surface water quality change. • Trends in water quality change of the seven major basins over 15 years were assessed. • Water quality change is related to both sewage interception and natural factors. • Water quality similarity was found between China's northern and southern basins. • Sewers perfection and non-point pollution control is key to promote water quality. [ABSTRACT FROM AUTHOR]

Identifying the response of runoff changes to extreme climate evolution was of great scientific significance for the rational regulation of watershed water resources and the prevention of hydrological disasters. However, the time–frequency response relationships were not clear. The Yinjiang River watershed, a typical watershed with karst trough valley areas, was chosen to identify the impact of different climatic driving factors on runoff changes from 1984 to 2015. Continuous wavelet transform (CWT), cross-wavelet transform (XWT), and wavelet coherence transform (WTC) were performed to study the response relationship and time–frequency effect between runoff changes and extreme climate change at different time scales. The main results showed that: (1) Twelve extreme climate indices (ECIs) were detected to have a significant impact on runoff changes, mainly on a 6-year time scale; (2) The R10 and Rx1day in extreme precipitation index and SU34.4 and TNx in the extreme temperature index were the main driving factors of runoff changes, which had relatively large impacts on runoff changes in high and low energy vibration regions. However, the remaining eight ECIs that passed the 0.05 confidence level showed relatively large impacts on runoff changes only in low energy vibration regions; (3) The transition of the interaction between ECIs and runoff changes in high and low time–frequency scales was related to the abrupt change characteristics of the ECIs. The correlation of abrupt change was an important reason for the emergence of highly correlated regions that trigger high and low energy vibrations; (4) As a whole, the extreme precipitation events were ahead of runoff changes at the high time–frequency scale and exhibited small lag effects at the low time–frequency scale, while extreme temperature events were mainly ahead of runoff changes. This study has effectively revealed the impact of climate factors at different scales on runoff changes, and provides a theoretical understanding for regulating and managing water resources in karst basins. [ABSTRACT FROM AUTHOR]

There has been controversy in theory and practice among studies about the governance of the "River Chief System" (RCS) policy and the watershed management issues behind it. This paper uses the regression discontinuity (RD) method and the water pollution monitoring data of 150 state-controlled monitoring points in China from 2007 to 2018 at the China National Environmental Monitoring Station to empirically study the effect of the "River Chief System" on water pollution treatment and the influencing factors behind the effect of the "River Chief System". The results show that the "River Chief System" policy has a positive impact on river pollution treatment in the observation term. The implementation effectiveness of the "River Chief System" is limited by factors such as the boundaries of the river chief's jurisdictions, the administrative conflict among river chiefs, local government environmental expenditure capacity, and environmental pressure. It is believed that the key to basin governance is to further improve the synergistic model of basin governance among regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • "Small-world" network characteristics of human-influenced river networks are found. • A dynamic connectivity index based on flow and probability density is proposed. • The hydrological connectivity response under the change of river networks is analyzed. • "Small-world" features of river networks lead to reduced hydrological connectivity. • Spatiotemporal heterogeneity of connectivity is related to the systemic function. River network connectivity is a key factor affecting watershed ecosystems and an important criterion for evaluating the health of river. The river network structure of the basin has changed dramatically in recent years due to human activity, but the response of connectivity to changes in physical structure is still poorly understood. In this paper, a dynamic index (connectivity index) based on daily-scale flow and probability density function is proposed to characterize the connectivity capacity of river networks. The Haihe River basin in China is selected as the study area, and a graphic model is constructed to assess the evolutionary structure of the river network. The 54 sections were classified into Low human impact (LHI) and High human impact (HHI), and the trends and causes of connectivity changes of the sections with the evolution of the network were analyzed. The results reveal that the river network degree and clustering coefficient keep increasing, the path length decreases and becomes more dense downstream, and the river network gradually evolves into a "small-world" network. The "small-world" characteristics improve the potential efficiency and specific functionality of the river network, but make the physical structure mismatch with the hydraulic gradient, and the network flow disperses severely, leading to a significant decrease in connectivity (HHI connectivity index is lower than LHI 52.1%). Moreover, the structural changes enhance the spatial and temporal differences in hydrological connectivity, which further restricts the function of the river system. "Small-world" and connectivity indicators (duration, start time, and intermittency) show strong correlations. Therefore, physical structure is an important factor influencing connectivity capacity of river networks. The planning and management of the watershed should consider the changes in hydrological connectivity caused by the structural modifications of the river network. [ABSTRACT FROM AUTHOR]

Understanding the changes in hydrological process is a key subject for water resource management of a high-diversity watershed. In this paper, through an establishment of a SWAT-based model, the effects of climate change and its induced vegetation change on hydrological process were analyzed in the East River Basin. The model could well simulate the hydrological processes of the basin including surface runoff (SURQ), groundwater (GWQ), lateral flow (LATQ), total water yield (WYLD), actual evapotranspiration (ET), and groundwater recharge (PERC). Under the vegetation change induced by temperature increase, the effects of the vegetation change on hydrological process were larger than that of the temperature change. Under the vegetation change caused by the increase of temperature and precipitation, the vegetation change enhanced the effects of climate change on annual SURQ, LATQ, GWQ, WYLD, and PERC of the basin. Under spatial scale, when the temperature and precipitation changed simultaneously, the increase of precipitation could promote the increase of annual ET in sub-watersheds. Also, the annual SURQ, WYLD, GWQ and ET in western sub-watersheds were more sensitive to the cumulative changes of vegetation and climate. This work can provide useful information to decision makers in water resource management of watersheds. • A SWAT-based model was established for a multi-level simulation. • Response of hydrological process to a climate-driven vegetation change was explored. • Effect of climate and vegetation changes on hydrological process was quantified. [ABSTRACT FROM AUTHOR]

Reference evapotranspiration (ET0) is an integral part of the regional hydrological cycle and energy balance and is extremely sensitive to climate change. Based on temperature data from 24 global climate models (GCMs) in the Coupled Model Intercomparison Project Phase 6 (CMIP6), this study developed a multi-model ensemble based on delta statistical downscaling with multiple interpolation methods and evaluation indicators to predict the spatial and temporal evolution trends of ET0 in the Yellow River Basin (YRB) under four emission scenarios (SSP126, SSP245, SSP370, and SSP585) for the near- (2022–2040), mid- (2041–2060), and long- (2081–2100) term future. Results demonstrate that regional data generated based on delta statistical downscaling had good simulation performance for the monthly mean, maximum, and minimum temperatures in the YRB, and the developed multi-model ensemble had better simulation capability than any single model. Compared to the historical period (1901–2014), the annual ET0 showed a highly significant increase for different future emission scenarios, and the increase is faster with increasing radiative forcing. The first main cycle of ET0 change was 52, 53, 60, and 48 years for the SSP126, SSP245, SSP370, and SSP585, respectively. ET0 in the YRB had positive values for EOF1 under all four emission scenarios, responding to a spatially consistent trend across the region. Compared to the historical period, the spatial distribution of ET0 under different future emission scenarios was characterized by being larger in the west and smaller in the east. As the radiative forcing scenario increased and time extended, ET0 significantly increased, with a maximum variation of 112.91% occurring in the western part of the YRB in the long-term future under the SSP585 scenario. This study can provide insight into the water cycle patterns of watersheds and scientific decision support for relevant departments to address the challenges of climate change. [ABSTRACT FROM AUTHOR]

Hydrological nonstationarity has brought great challenges to the reliable application of conceptual hydrological models with time-invariant parameters. To cope with this, approaches have been proposed to consider time-varying model parameters, which can evolve in accordance with climate and watershed conditions. However, the temporal transferability of the time-varying parameter was rarely investigated. This paper aims to investigate the predictive ability and robustness of a hydrological model with time-varying parameter under changing environments. The conceptual hydrological model GR4J (Génie Rural à 4 paramètres Journalier) with only four parameters was chosen and the sensitive parameters were treated as functions of several external covariates that represent the variation of climate and watershed conditions. The investigation was carried out in Weihe Basin and Tuojiang Basin of Western China in the period from 1981 to 2010. Several sub-periods with different climate and watershed conditions were set up to test the temporal parameter transferability of the original GR4J model and the GR4J model with time-varying parameters. The results showed that the performance of streamflow simulation was improved when applying the time-varying parameters. Furthermore, in a series of split-sample tests, the GR4J model with time-varying parameters outperformed the original GR4J model by improving the model robustness. Further studies focus on more diversified model structures and watersheds conditions are necessary to verify the superiority of applying time-varying parameters. [ABSTRACT FROM AUTHOR]

• We developed an integrated model to quantify biodiversity by habitat quality. • Cultivated land mainly transfers into woodland, with some of construction land. • Biodiversity habitat quality under ecological protection scenarios is best. • The biodiversity of the upper and lower reaches in 2030 shows trend of improvement. The temporal and spatial dynamics of biodiversity and its future trends are of great significance for maintaining biodiversity pattern and ensuring regional ecological security in the Nanliu River Basin of Beibu Gulf. At present, most studies are concerned with the assessment of biodiversity in historical period, but few studies focused on the prediction of biodiversity under several scenarios in future years, and the history and future spatial simulation of habitat quality has not been carried out. Therefore, the establishment of biodiversity simulation studies under different scenarios in the future plays a crucial role in the sustainable development of regional social economy. This study takes Nanliu River Basin, which only flows into the sea in the Beibu Gulf, as the research object. Based on land use data and social and economic data interpreted from remote sensing data in 2000, 2010 and 2020, Conversion of Land Use and its Effects at Small Region Extent (CLUE-S) model was used to simulate and predict land use patterns for ecological protection scenarios, natural growth scenarios and food security scenarios in 2030. The Integrated Valuation of Ecosystem Service and Tradeoff (InVEST) model was used to evaluate the biodiversity of different scenarios in the past and future and discuss the habitat quality and degradation degree of biodiversity in the watershed. Results were presented as follows. In 2000–2020, an increasing trend of construction land, shrub land and water area was found in the Nanliu River basin of Beibu Gulf. The largest increase was observed in construction land, and the largest decrease was noted in cultivated land and woodland. The best habitat quality will be under the ecological protection scenario in 2030. The biodiversity in the upstream and downstream of the three scenarios showed varying degrees of improvement, and the midstream exhibited a degradation trend. The research results of this paper can make up for the vacancy of biodiversity habitat evaluation system in Nanliu River Basin at home and abroad, and have important theoretical and practical significance for promoting ecological protection and ecological planning of watershed. [ABSTRACT FROM AUTHOR]

Owing to the publicity and externality of watershed governance, collaborative governance among cities has become an inevitable choice to improve watershed governance performance and promote sustainable development of watersheds. Existing studies have provided many enlightenment on promoting watershed collaborative governance (WCG), while most of them investigated WCG from single or several dimensions with scanty quantitative empirical studies. Against this background, this study aims to establish a comprehensive WCG research framework involving multiple phases and diverse actors to empirically measure the synergy degree of WCG. Specifically, this study constructs a WCG index system composed of resource investment, open cooperation, and performance supervision subsystems that involves actors of government, enterprise, and the public. Using the complex system synergy model, an empirical analysis is performed to evaluate the synergy degree of Taihu Basin collaborative governance among and within cities in Jiangsu province, China during 2014–2020. The results reveal that the Tai Basin collaborative governance among cities was still in the run-in adaptation stage, which was primarily constrained by the discrete open cooperation subsystems among cities. The synergy degree of Taihu Basin collaborative governance within cities presented significant differences. Several targeted implications are proposed according to the results. This study provides a comprehensive index system for synergy degree measurement of WCG and could offer effective guidance for policymakers to design effective strategies for improving WCG performance. [ABSTRACT FROM AUTHOR]

Research Highlights: Land use/cover change (LUCC) has an impact on the water use efficiency (WUE) of green space in the Haihe River Basin. Background and Objectives: The Haihe River Basin has historically been one of the most water-stressed basins in China. With the increase in green space and economic development, land use and water use in the Haihe River Basin have changed significantly. In order to contribute to the sustainable development of basin water management, the impacts of LUCC on the WUE of the Haihe River Basin were assessed with the goal to support decision makers with regard to water resources planning and watershed management. Materials and Methods: (1) Moderate Resolution Imaging Spectroradiometer (MODIS) data and land use data were used to produce land use/land cover and other related maps. (2) The WUE equation was used to calculate the green space WUE. (3) The contribution rates of changes in land use were assessed to illustrate how LUCC affected green space WUE. Results: (1) Artificial surfaces increased and large areas of farmland were converted to non-agricultural use, accompanied by the addition of green space. (2) Green space WUE increased significantly from 2005 to 2015. The average annual WUE exhibited a relatively uniform spatial distribution in the Haihe River Basin. Except for the central area of urban land, the WUE of most areas exhibited an increasing trend. (3) The impact of LUCC on WUE was mainly a result from the conversion of farmland and artificial surfaces and the increase in green space. Ecological restoration and crop adjustment contributed greatly to the improvement in green space WUE in the basin. Conclusions: Green space WUE of the Haihe River Basin was significantly affected by LUCC and there is room for improvement in the WUE of green spaces in the basin. The paper concludes with recommendations for further research to assist in planning for green space to promote sustainable development related to land use and water management. [ABSTRACT FROM AUTHOR]

Being one of the most important sources of water in the Jilin Province in China, the Yinma River Basin (YRB) is facing problems of water scarcity in low economic areas and low utilization in richer areas mainly caused by the irrational allocation of water, excessive pursuit of economic benefits, and neglect of environmental problems. Restricting watershed development involves potential decision-making risks. Some scholars have used the interval two-stage stochastic planning method to adjust water resource allocation in the Drinking Horse River Basin, but the method uses historical statistics for projection and does not take into account the ambiguity and uncertainty in real planning situations. Therefore, this study addresses the problems prevalent in the allocation of water resources in the YRB through optimization using stochastic programming methods, interval and two-stage, and introduces the fuzzy mathematical programming method, with the aim of coordinating the water balance of various water-consuming sectors in the YRB, so as to reconfigure the water allocation. The goal is to solve the existing problems of irrational water allocation, reduce system risks posed by excessive economic development, mitigate water shortages in the water-consuming sectors, and alleviate potential decision-making risks and vague uncertainties associated with the allocation of water resources. Additionally, optimization of the pollution-holding capacity improvement project was carried out. The interval fuzzy two-stage model simulation developed in this study shows that the distribution of water across the different administrative regions can be reduced by up to 30% compared with the original model, effectively reducing the problem of water wastage. Post-optimization, the impact of water shortage in the water resources allocation scheme is alleviated to a significant degree, and there is no water shortage in some areas. At the same time, the eco-environmental sector has gradually taken the leading role in the distribution of water reuse among the different water-consuming sectors. The pollution-holding capacity has been enhanced, and the discharge and river entry chemical oxygen demand (COD) and ammonia nitrogen, two typical pollutants, have been reduced. The membership interval in the interval fuzzy two-stage model reflects the relationship between the possible level of the target value and the risk level. This study provides a guideline for decision makers for balancing the relationship between benefits and risks and proposes a planning scheme that is more conducive to the development of the river basin. [ABSTRACT FROM AUTHOR]

Under the influence of climate change, the hydrological processes of glaciers have undergone significant changes, a fact which is seriously affecting agricultural production in the downstream region of the Tianshan Mountains, China. In order to explore the intrinsic relationship between climate change and hydrological elements, we proposed an "evaluation-driving-prediction" system to study it. First, we constructed a glacier-enhanced soil and water assessment tool model (GE-SWAT) and used a two-stage calibration method to optimize the model parameters. Next, a scenario analysis was used to evaluate the driving factors of historical runoff changes. Finally, we projected future runoff changes using bias-corrected regional climate model (RCM) outputs. The results of the case study on the Jinghe River Basin in the Tianshan Mountains show that from 1963 to 2016, total runoff increased by 13.3%, 17.7% of which was due to increasing precipitation and 1.8% of which was negated by rising temperatures. The glacier runoff increased by 14.5%, mainly due to the rising temperatures. A 3.4% reduction in snowmelt was caused by a lower snowfall/precipitation ratio, which significantly reduced the snowfall from June to August. The RCM projection indicated that the warming and humidification phenomenon in the study area will continue at least through to the mid-21st century. A consistent increase in glacier runoff and total runoff is projected, but the contribution rate of the glacier runoff will have little to no change under the RCP4.5 and RCP8.5 emission scenarios. Our research demonstrates the simulation performance of the GE-SWAT model in a basin with moderate glacier cover. This method is shown to be efficient in quantifying the impact of climate change on glacier hydrological processes and predicting future streamflow changes, providing a good research reference for similar regions. [ABSTRACT FROM AUTHOR]

To assess the impact of four-dimensional variational (4D-Var) data assimilation on the performance of a land--atmosphere coupled model, the satellite precipitation of the Integrated Multisatellite Retrievals for Global Precipitation Measurement (IMERG) was assimilated into the Weather Research Forecast (WRF) Model, and the WRF was coupled to the hydrological model TOPX. Precipitation and evaporation were both investigated as connecting elements in the coupled model WRF--TOPX. Differing in whether the 4D-Var data assimilation and evaporation were applied, one control experiment and four experiments were performed to simulate a historical flood event that happened in the Wangjiaba watershed in eastern China. The key hydrological variables of precipitation, potential evaporation, soil moisture, and discharge in the studied flood process were evaluated. The results showed that 1) the 4D-Var data assimilation with the IMERG could reduce both the overestimations of the WRF-predicted precipitation and potential evaporation; 2) the applied 4D-Var data assimilation could improve considerably the accuracy of the soil moisture and discharges from the coupled model WRF--TOPX; and 3) evaporation was also an important factor to influence the net precipitation to affect the performance of the coupled land--atmosphere model. With the two connecting elements of precipitation and evaporation, the 4D-Var assimilation based on IMERG could improve the Nash--Sutcliffe coefficient of the coupled model WRF--TOPX from 0.483 to 0.521 at the hourly scale. These investigations can provide important implications for the land--atmosphere coupling with both the precipitation and evaporation and using the 4D-Var data assimilation with IMERG for flood simulation at a large scale. [ABSTRACT FROM AUTHOR]

Understanding the relationship between land use and surface water quality is necessary for effective water management. We estimated the impacts of catchment-wide land use on water quality during the dry and rainy seasons in the Dongjiang River basin, using remote sensing, geographic information systems and multivariate statistical techniques. The results showed that the 83 sites can be divided into three groups representing different land use types: forest, agriculture and urban. Water quality parameters exhibited significant variations between the urban-dominated and forest-dominated sites. The proportion of forested land was positively associated with dissolved oxygen concentration but negatively associated with water temperature, electrical conductivity, permanganate index, total phosphorus, total nitrogen, ammonia nitrogen, nitrate nitrogen and chlorophyll-a. The proportion of urban land was strongly positively associated with total nitrogen and ammonia nitrogen concentrations. Forested and urban land use had stronger impacts on water quality in the dry season than in the rainy season. However, agricultural land use did not have a significant impact on water quality. Our study indicates that urban land use was the key factor affecting water quality change, and limiting point-source waste discharge in urban areas during the dry season would be critical for improving water quality in the study area. [ABSTRACT FROM AUTHOR]

Understanding the characteristics of non-point sources (NPS) pollutions can provide theoretical support for improving water quality. Siheshui watershed located in south China was selected to explore the characteristics of NPS pollutions in rainfall-runoff process. In this small agricultural watershed, five flood events and one non-flood event were monitored, and the water quantity and quality constituents were measured. The event mean concentrations (EMCs) of pollutant constituents in runoff flows were estimated. It is shown that the EMCs of BOD5, CODMn, TSS, TP, TN, and NH3-N in the flood events are remarkably larger than those in the non-flood event. The antecedent precipitation has a large effect on the output of the pollutant concentration. The pollutant load fluxes of most pollutant constituents change synchronously with the runoff flows, and the synchronization relationship is better than that between the pollutant concentrations and the runoff flows. The Pearson correlation analysis indicates that the EMCs of CODMn, TP, and TSS are significantly correlated with rainfall runoff characteristics in the flood events, while BOD5, TN, and NH3-N show weak correlations. In addition, the mean concentration method was used to estimate the annual NPS pollution load. It is shown that the proportions of the NPS pollution load to the total pollutant load are more than 80% from 2008 to 2010. [ABSTRACT FROM AUTHOR]

To evaluate the effect of comprehensive management on runoff and sediment reduction in meso-scale watersheds, the Yanwachuan watershed of Loess tableland gully region in China was investigated. Variation trends of the runoff and sediment from 1981 to 2009 were analysed, and the year of abrupt change was identified using the double mass curve method, accumulative departure method, moving t-test method and Yamamoto method. Next, the effects of comprehensive management on runoff and sediment reductions were quantitatively evaluated based on the runoff/sediment coefficient method and double mass curve method, both capable of separating the effect of climate change from that of comprehensive management. Finally, the driving forces of runoff and sediment variations were discussed from both climatic and comprehensive management aspects. The results showed that the runoff and sediment in the watershed had significantly decreased since an abrupt change in 1997. During the change period (1998-2009), the erosive precipitation and precipitation erosivity had been reduced by 32.4% and 17.4%, respectively, compared with the base period (1981-1997); the areas of forest and grass had increased; and the normalized difference vegetation index (NDVI) had increased by 20.6% with significantly enlarged vegetation coverage. The benefit value of runoff reduction and sediment reduction were 27.3% and 76.2%, respectively. The resultant runoff and sediment reductions in the watershed were the synergy of climate change and comprehensive management, with greater than 90% reduction contributed by comprehensive management. All these results supported that comprehensive management played the dominant role in runoff and sediment reductions. [ABSTRACT FROM AUTHOR]

To tackle China's pervasive water pollution, tremendous efforts are needed to achieve more and better information. However, resources for information collection (e.g., water quality monitoring, field experiments, etc.) are very limited for large watersheds with significant nonpoint source pollution. Thus, it is crucial to identify the priority of information acquisition. Based on the theory of value of information (VOI), a stochastic optimization approach was developed in this study to evaluate the importance of information. The approach was applied to several key polluted water bodies in China (e.g., Lake Taihu, Lake Chaohu, and Lake Dianchi). The major findings include: (1) because of the severe pollution and large uncertainty, the VOI for the targeted water bodies is substantial; (2) when the uncertainty is significant, a stricter regulation would result in a higher VOI, and therefore provide more incentives for data collection; (3) due to the interaction among different information sources, collecting multiple types of information simultaneously could be more valuable than collecting one after another; and (4) the importance of a specific type of information could vary significantly across watersheds. The proposed approach can be readily extended to more complex models and more sophisticated watershed cases. It could effectively support watershed management in China, as well as in other countries. [ABSTRACT FROM AUTHOR]

Environmental problems are closely related to human societies' processing of materials. Along with a rapid economic growth, lake eutrophication has received broad attention in the last two decades in China. As phosphorus is the dominant nutrient in lake environments, this study attempts to examine how human societies extract, utilize and release phosphorus which subsequently leads to eutrophication. Applying substance flow analysis (SFA) approach for the case of Dianchi Lake in southern China, this study establishes a statistical model by balancing the physical quantities of phosphorus flows in 2000. Resource extraction, phosphate industries, agricultural production, livestock breeding, and human living are given focused attentions in the SFA model. The results showed water environment is largely dependent on the local phosphorus metabolism, and thus, if the related phosphorus flows, particularly referring to recycling and wastes flows, could not be re-organized towards a more ecological direction, Dianchi Lake would be unavoidably and continuously suffering eutrophication. Aiming at ecological restructuring of the phosphorus metabolism with respect to economic efficiency and environmental effectiveness, critical options are discussed and future directions in relation to both societal and policy aspects are presented. [ABSTRACT FROM AUTHOR]

Analyzing the spatiotemporal characteristics and causes of landscape pattern changes in watersheds around big cities is essential for understanding the ecological consequence of urbanization and provides a basic reference for the watershed management. This study used a land-use transition matrix and landscape indices to explore the spatiotemporal change of land use and landscape pattern over Liuxihe River basin of Guangzhou in the southeast of China from 1980 to 2015 with multitemporal Landsat satellite data in response to the rapid urbanization process. Primary temporal and spatial influencing factors were first quantitatively identified through grey relation analysis (calculating correlation degree between land use changes and influencing factors) and Geodetector (detecting landscape spatial heterogeneity and its driving factors), respectively. Considerable spatial and temporal differences in land use and landscape pattern changes were observed herein, thus determining the influencing factors of these differences in the Liuxihe River basin. These changes were characterized by a large increase in construction land converted from cropland, particularly in the middle and lower reaches of the basin from 2000 to 2010, causing dramatic fragmentation and homogenization of the landscape pattern there. Meanwhile, the landscape pattern gradually transitioned from an agricultural land use dominant landscape to a construction land use dominant landscape in these regions. Furthermore, the rapid growth of a nonagricultural population and the transformation of industry primarily caused the temporal changes of landscape pattern, and the landscape spatial heterogeneity was mainly caused by the interaction of complicated geomorphology and anthropogenic activities in different spatial locations, particularly after 2000. This study not only provides an improved approach to quantifying the main spatiotemporal influencing factors of landscape pattern changes during different time periods, but also offers a reference for decision-makers to formulate optimal strategies on ecological protection and urban sustainable development of different regions in this study area. [ABSTRACT FROM AUTHOR]

Understanding and quantifying changes in hydrological systems due to human interference are critical for the implementation of adaptive management of global water resources in the changing environment. To explore the implications of hydrological variations for water resources management, the Wuding River Basin (WRB) in the Loess Plateau, China, was selected as a case study. Based on the Budyko-type equation with a time-varying parameter n, a human-induced water–energy balance (HWEB) model was proposed to investigate the hydrological variability in the WRB. The investigation showed that runoff continuously reduced by 0.424 mm/a during 1975–2010, with weakly reducing precipitation and increasing groundwater exploitation causing a decrease in groundwater storage at a rate of 1.07 mm/a, and actual evapotranspiration accounting for more than 90% of precipitation having an insignificantly decreasing trend with a rate of 0.53 mm/a under climate change (decrease) and human impact (increase). Attribution analysis indicated that human-induced underlying surface condition change played a dominant role in runoff reduction by driving an increase in actual evapotranspiration, and that mainly impacted the overall decrease in runoff compounded by climate change during the entire period. It is suggested that reducing the watershed evapotranspiration and controlling groundwater exploitation should receive greater attention in future basin management. [ABSTRACT FROM AUTHOR]

The River Chief System (RCS) is an effective measure for China to solve complex water problems and maintain the health of rivers and lakes. It is an institutional innovation to improve the water governance system and ensure national water security. Guiding and encouraging the public to participate in the construction of the RCS can promote the improvement of the level of social governance. The RCS is an effective supplement and supervision to the performance of the river chief and related departments, which can effectively promote the transformation of the RCS from nominal to practical and efficient. This study summarizes the innovative models and practical effects of, and public participation in, the RCS, analyzes the prominent problems, and proposes some measures to maximize the influence of public participation. The study provides insights on how to ensure the long-term operation of the RCS, a reference for countries around the world as a suitable solution for the sustainable management of water environments. [ABSTRACT FROM AUTHOR]

Forest harvesting and hydropower dams can significantly affect flow regimes (magnitude, timing, duration, frequency, and variability), resulting in changes in degraded aquatic ecosystems and unstable water supply. Despite numerous studies on the effects of forest harvesting on mean flows, the impact of forest harvesting on flow regimes has been less investigated. A great difficulty lies in separating the hydrological effect of forest harvesting from that of climate variability and other watershed disturbances such hydropower dams. In this study, the Upper Zagunao River watershed (2242 km2) was selected as an example to provide a quantitative assessment of the effects of forest harvesting and hydropower dams on low flow regimes. The key findings include: (1) Forest harvesting led to a significant reduction in the magnitude and return period of low flows, and a significant increment in the variability and duration of low flows; (2) the recovery of low flow regimes occurred 40 years after forest harvesting as forest recovery processed; and (3) hydropower dams caused significant impact on all components of low flow regimes, e.g., a reduction in the magnitude, return period, and timing of low flows, and an increment in the variability and duration of low flows. Our findings highlight the negative impact of both forest harvesting and hydropower dams on low flow regimes in the Upper Zagunao River watershed. A watershed management strategy for offsetting the negative effect of hydropower dams on low flow regimes by restoring hydrological functions of subalpine forests is highly recommended in subalpine watersheds of the Upper Yangtze River. [ABSTRACT FROM AUTHOR]

Flash floods in mountainous areas have become more severe and frequent as a result of climate change and are a threat to public safety and social development. This study explores the application of distributed hydrological models in flash floods risk management in a small watershed in Sichuan Province, China, and aims to increase early warning lead time in mountainous areas. The Hydrologic Engineering Center's Hydrologic Modeling System (HEC-HMS) model was used to simulate the flash flood process and analyze the variation in flood hydrographs. First, the HEC-HMS model was established based on geospatial data and the river network shape, and eight heavy rainfall events from 2010 to 2015 were used for model calibration and validation, showing that the HEC-HMS model was effective for the simulation of mountain floods in the study area. Second, with the assumption that rainfall and flood events have the same frequency, the flood hydrographs with different frequencies (p = 1%, 2%, 5%, and 10%) were calculated by the HEC-HMS model. The rising limbs of the flood hydrographs were significantly different and can be divided into three parts (0–5 h, 6–10 h, and 11–15 h). The rising rate of the flood stage for each part of the flood hydrograph increases in multiples. According to the analysis of the flood hydrographs, two critical early warning indicators with an invention patent were determined in the study: the flood stage for immediate evacuation and the rising rate. The application of the indicators in the study shows that it is feasible to advance the time of issuing an early warning signal, and it is expected that the indicators can offer a reference for flash flood early warning in the study area and other small watersheds in mountainous areas. [ABSTRACT FROM AUTHOR]