Study region Shaxi River Basin of China. Study focus Accurate simulation of water cycle components is critical for understanding basin hydrological processes and supporting water resources management. This study evaluates the performance of the SWAT model under two calibration strategies: dual-objective lumped calibration of streamflow and evapotranspiration (ET) (M1) and dual-objective spatially distributed calibration (M2). Model calibration and validation were conducted using observed outlet streamflow and spatially distributed ET data, and terrestrial water storage change (TWSC) was estimated based on water balance analysis. New hydrological insights for the region Both calibration strategies reproduce the temporal dynamics of streamflow and ET, while M2 demonstrates consistently superior performance. For streamflow, M2 improves NSE from 0.73 to 0.94 during calibration and from 0.51 to 0.89 during validation, with PBIAS reduced from 15.04–17.45% to 3.79–5.10%. For ET, PBIAS decreases from −3.31% to 0.69% during calibration and from −7.98% to −2.79% during validation. Spatially, M2 enhances sub-basin ET simulation, with NSE generally increasing and systematic biases reduced across most sub-basins. ET-related parameters exhibit physically consistent relationships with soil types and vegetation cover, indicating improved representation of underlying surface heterogeneity. Long-term simulations reveal pronounced spatial gradients, with precipitation and runoff decreasing from northwest to southeast, ET increasing from west to east, and TWSC showing relatively limited spatial variability. Overall, spatially distributed dual-objective calibration improves both the accuracy and spatial consistency of water cycle simulations, providing a robust framework for hydrological modeling in heterogeneous basins.

Tropical cyclones and frontal systems are two primary weather systems influencing East Asia. Distinguishing between typhoon rainfall (TR) and non-typhoon rainfall (non-TR) and analyzing their divergent changes are essential for exploring extreme rainfall evolution. Existing related researches remain limited and have primarily focused on a single timescale (annual or seasonal), overlooking characteristics across other timescales. Fujian was selected as a typical case due to its distinctive geographic environment. This study adopted total rainfall and maximum daily rainfall to compare long-term trends of typhoon-related extreme rainfall (TER) and non-typhoonrelated extreme rainfall (non-TER) across multiple timescales and their spatial patterns. There were divergent timescale effects in trends of TER and non-TER in Fujian (1961-2021). While no significant trends are found at annual and typhoon-season scales, TER showed a significant increasing trend for August. In contrast, non-TER displayed a significant upward trend for typhoon season, but not at other timescales. Temporally, concentrated typhoon frequency and increased typhoon linger time in August were primary drivers of the significant TER increase during same period. Spatially, the combined influences of terrain and typhoon tracks resulted in a greater relative increase in August TER in the western region than the eastern region, creating a distinct west-east divergence: significant increases in the west contrasted with minimal changes in the east. By distinguishing between TR and non-TR, analyzing regional extreme rainfall variability offers a newer insight into its evolution under distinct weather systems across East Asia.

To enhance extreme rainfall risk assessment in East Asia, it is critical to distinguish typhoon and non-typhoon rainfall, assessing the spatiotemporal patterns of their extreme rainfall hazards and conducting corresponding spatial zonation. Taking Fujian, China’s southeastern coast, as a typical case, three extreme rainfall indices and a combined weighting method of entropy weight and an analytic hierarchy process were used to analyze the spatiotemporal patterns of typhoon extreme rainfall and non-typhoon extreme rainfall hazards, followed by spatial zonation based on their spatial differences. The results showed remarkable spatiotemporal heterogeneity in these two types of hazards in Fujian. Temporally, the non-TER hazard was generally higher, with the average hazard being 0.193 and peaking in June. In contrast, the TER hazard occurred primarily from July to September, with an average of 0.156 and a peak in August. Spatially, the TER hazard exhibited greater heterogeneity, increasing from the western inland region to the eastern coast, whereas the non-TER hazard displayed the opposite pattern. Fujian can be divided into three zones of extreme rainfall hazard: non-typhoon-dominated zone, typhoon-dominated zone, and typhoon and non-typhoon co-dominated zone. This study provides a newer perspective for extreme rainfall hazard assessment in East Asia and offers targeted guidance for disaster prevention and mitigation.

Accurate estimation of evapotranspiration (ET) is crucial for watershed eco-environmental research and applicability of ET products in southeastern coastal basins of China needs to be evaluated. We proposed an improved evaluation framework for basin applicability of ET products. Based on assessing the overall rationality and correcting ET products using water balance method, the temporal dynamics of corrected products ET (ETC) were assessed by dual-variable calibrated SWAT model. Application of this framework in three basins in southeastern coastal China showed that three corrected products ET were consistent in magnitude, but differed markedly in inter-annual and intra-annual variability. Compared with SWAT-ET, ETC_SSEBOP exhibited a better performance in temporal dynamics, followed by ETC_FLDAS, and ETC_MOD16A2 was the worst. The simulation performance of products on forestland ET was a potential influencing factor to these differences. The proposed assessment framework for ET products provided a more holistic assessment of their applicability, yielding more reliable results.

This study presents a case study of Typhoon Maria (2018) affecting Yacheng Town, Xiapu County, Fujian Province, China, to investigate how typhoon landfall timing relative to the astronomical tide influences seawall breaching and flood evolution under storm surge conditions. The study employs the MIKE 21 model, SWAN model, and DLbreach model to simulate the breach process and flood inundation under different typhoon landfall timings. The findings indicate that the storm surge effect intensifies with earlier typhoon landfall, and the typhoon waves are positively correlated with the water level. Additionally, adjusting the typhoon landfall time by three hours earlier or later significantly reduces the flood inundation area, but adjusting it by one hour has little effect. The quantitative results are specific to this case study of Typhoon Maria at Yacheng Town. These findings provide a crucial scientific basis and reference for the formulation of disaster prevention and mitigation measures for seawalls and the design of coastal engineering projects.

Study region: Jianxi Watershed (JXW) and Shanmei Reservoir Watershed (SRW), located in southeastern coastal China. Study focus: The SWAT model is a widely used hydrological simulation tool. However, the impact of different model development methods and the variation of sensitive parameters across time scales on simulation performance remains insufficiently studied. This study focused on the effects of time-scale on SWAT model runoff simulation performance by applying independent and unified development methods for model setup. Runoff simulations were conducted at annual, monthly, and daily time scales. The simulation performance differences between the two methods were compared, variations in sensitive parameters across time scales were analyzed, and their underlying mechanisms were explored to optimize SWAT model development and improve simulation reliability. New hydrological insights for the region: (1) The simulation results of the SWAT model with the independent development method were all better than that of the unified development method. (2) The sensitive parameters of the models at the annual, monthly, and daily time scales exhibited significant differences. There were just 4 common parameters across the different time scales for the 2 regions, which were the surface runoff parameter CN2, the groundwater-related parameters ALPHA_BF and RCHRG_DP, and the evapotranspiration-related parameter ESCO. (3) The values of the four common sensitive parameters were varied with the time-scale, which was a key factor contributing to the superior simulation performance of the independent development method over the unified method.

Rainfall in East Asia is affected by two rain-bearing systems: tropical cyclones and monsoon-related frontal systems. Distinguishing typhoon rainfall (TR) and non-typhoon rainfall (non-TR) helps to understand the evolution process of regional rainfall at different timescales. Taking Fujian Province in the southeast coast of China as an example, based on the fixed box approach of separating TR, the method of determining the size of fixed box is explored. TR and non-TR are separated in Fujian Province, and the spatial variations of TR and non-TR at different timescales (annual, monthly, day of annual-maximum-rain) are analysed. The results showed that (1) according to the relationship between the sizes of fixed box and the rate of change of TR, the size of fixed box could be reasonably determined; thus, the expended size of fixed box suitable for separating TR in Fujian was 3.5 degrees, namely the range of 20 degrees-31.8 degrees N and 112.3 degrees-124.2 degrees E. (2) The spatial variations of TR at different timescales in Fujian were similar: TR decreased from the coast to the inland, and the northeast coast of Fujian was the high-value region. Due to the difference of water vapour sources, non-TR in March-June increased from the coast to the inland, but the high value of non-TR in July-September was distributed in the eastern coast. (3) The contribution rates of average TR to the total rainfall of the year, July-September and 1 day were 12.8%, 34.6% and 35.7%, respectively. In eastern coast, TR in July-September accounted for 1/3-1/2 of total rainfall, and the rainfall in a day was mainly affected by TR; while in western inland, rainfall was mainly non-TR and the influence of TR was less than 1/4. We explore a method to determine the size of fixed box for separating regional typhoon rainfall (TR). TR accounts for 12.8% of annual rainfall and 35.6% in July-September in Fujian, which is a major threat in the coast in terms of extreme rainfall. The spatial variations of TR at different timescales are similar but non-TR are different. image

ABSTRACT The water velocity undergoes a significant increase during the initial stage of floods. The present study focuses on investigating the scours and silting occurring in an S-shaped gravel-bed river. The primary objective is to analyze the impact of 10-year flood events on both the riverbed and bank stability. This river is located in the Sai-jiang River reach, Fujian Province, China. A numerical model of riverbed scours and silting is herein tested. The research results indicate that the morphological evolution of the whole river section is affected in the early stage of flood evolution; however, in the later stage, some key places such as the bridge and the river land are still greatly affected. The apex of the river bend is in close proximity to the downstream river island, resulting in scour at the head of the river island that deviates from conventional patterns of head scour and tail siting. Furthermore, the presence of artificial structures like bridges exacerbates the scour and silting processes in river beds during flood events. For this case, the riverbed adjacent to the Banzhong Bridge pier experienced a widening of approximately 50 m and downstream extension of around 300 m, with a maximum vertical scouring depth of 2.87 m.

In the context of global change, it is vital to comprehensively understand the spatial pattern and driving mechanism of vegetation growth to maintain the stability of watershed ecosystems. Previous research has focused mainly on identifying the main drivers of vegetation growth, while the direct and indirect effects of climate, terrain, and human activity on vegetation growth have rarely been explored. This study used the Minjiang River Basin (MRB), an important ecological barrier and the largest watershed in southeastern China, as an example. The kernel normalized difference vegetation index (kNDVI) was calculated on the Google Earth Engine (GEE) platform to examine the spatial pattern and evolution characteristics of vegetation growth. The optimal parameter -based geographical detector (OPGD) and partial least squares structural equation modeling (PLS-SEM) were used to analyze how terrain, climate, and human activity influenced the spatial pattern of the kNDVI. (1) From 2001 to 2020, vegetation growth in the MRB was predominantly rated as excellent or good, and 88.93% of the area showed an increasing trend of vegetation growth. (2) The OPGD revealed that the primary drivers influencing the spatial distribution of the kNDVI in the MRB included population density, nighttime light, elevation and temperature, which explained >40% of the variation in the kNDVI. The interaction of all paired drivers enhanced the explanatory power of the kNDVI, among which the strongest interaction was between population density and elevation, and the second interaction was between population density and temperature. (3) PLS-SEM revealed that human activity had a direct negative effect on the kNDVI, while terrain and climate had direct and indirect positive effects on the kNDVI. Overall, the total effects of terrain, climate and human activity on the kNDVI were 0.594, 0.233 and - 0.495, respectively, indicating that the positive effect of terrain outweighed the negative effect of human activity on vegetation growth in the MRB. These findings not only provide scientific evidence for ecological conservation and management in the MRB but also offer a useful reference for other regions exploring the complex causes of spatial patterns of vegetation growth.

Study region: Southeast coast of China Study focus: The reservoirs in southeast coast of China are mostly small due to the limitations of terrain. In order to analyze the impact of these densely distributed small and medium-sized reservoirs (SMRs) with lacking observation and operational data on runoff, this paper uses a hydrological model & scenario simulation method to separate the impacts of climate variability (CV), land use change (LUC) and SMRs group change on streamflow variation in two river basins of Southeast China. New hydrological insights for the region: (1) The streamflow of two basins has changed greatly, with CV and SMRs change being the main influencing factors, while the impact of LUC was relatively small. The contribution rates of CV to the annual runoff change of three hydrological stations in two river basins were 90.19%, 61.75% and 26.64%; Contribution rates of SMRs changes were 9.34%, 37.24% and 71.04%, correspondingly. (2) The regulation of streamflow by SMRs changes led to a decrease in both annual and monthly runoff, which was due to the fact that the main functions of SMRs in this region are agricultural irrigation and domestic water supply. (3) The three-factor separation method based on hydrological modeling, which separated the cumulative effects of SMRs in the form of SMRs group, would be valuable for the study and management of watersheds with numerous SMRs and lack of observation and operational data.

This study aimed to effectively evaluate the ecological restoration of the river reach where a small hydropower station was retired or renovated. An ecological health index system was constructed based on the environmental characteristics of the upstream and downstream of the small hydropower station after its retirement and renovation. Based on the combination weighting concept of game theory, the combination weights were obtained by the comprehensive analytic hierarchy process (subjective weight) and entropy method (objective weight). This ecological health assessment with fuzzy comprehensive evaluation was applied to assess the health status of Shimen (dam removal) and Changqiao (renovation in ecological flow) reaches of the Tufang River in Changting County, China. The results showed that the ecological health assessment index system proposed in this study was comprehensive and reasonable, and the revision degree of the hydropower station obviously influenced the process of ecological river restoration. The findings from this study would benefit for the rational utilization of water resources and the river ecological health maintenance in mountainous areas.

Study region: Minjiang River Basin of China. Study focus: This paper aimed to study the spatiotemporal changes in water cycle components including evapotranspiration (ET) and terrestrial water storage in a watershed. To achieve this, we proposed a method that is based on the water balance and utilizes measured annual precipitation and runoff data to correct ET products. Subsequently, we derived the annual terrestrial water storage changes and performed trend analysis on the water cycle components by the MannKendall trend test. New hydrological insights for the region: (1) The Global Land Data Assimilation System (GLDAS) product overestimated ET from 2000 to 2019 in the Minjiang River Basin (MJB), which was 105.18 mm higher than ET. Through sub-basin validation, the relative error between the corrected ET and the ET is less than 5.1%. The proposed method can construct a reasonable annual dataset of water cycle components. (2) From 2000-2019, the Minjiang River Basin witnessed nonsignificant increasing trends in precipitation and runoff. However, significant growth was observed in ET, indicated by a Mann-Kendall trend test Z-value of 2.63. The variation in ET was primarily influenced by the normalized difference vegetation index (NDVI) (correlation coefficients of 0.37) and temperature (correlation coefficients of 0.48). The terrestrial water storage change fluctuated between - 400 and 355 mm. The relationships among the water cycle components, as represented by the runoff coefficient and evapotranspiration coefficient show nonsignificant changing trends. Both displayed a non-significant decreasing trend. From 2000-2019, the water cycle process remained relatively stable under changing environments in the MJB.

Most of the methods using digital elevation models (DEM) to extract water systems require the determination of catchment area thresholds.For a better understanding of the rationality and applicability of several commonly used determination methods of the catchment area threshold for water system extraction,the distance error between the real river source and the extracted one is used as a criterion to determine the rationality of the real water system extraction methods.Four main methods,namely,the drainage density method,the water-system fractal dimension method,the method of the minimum error at the river source,and the channel branching ratio method,are selected,and the Jinjiang River Basin on the southeast coast is taken as an example.The distance errors between the extracted river sources by different methods and the real river sources are compared.The results show that the visual discrimination of the catchment area threshold used by the drainage density method,water-system fractal dimension method,and channel branching ratio method has a large uncertainty,and the distance errors are large.In the method of the minimum error at the river source,the catchment area threshold is determined according to the minimum distance error between the extracted river source and the real one,which is unique.Hence,it is a more reasonable method among the four DEM-based real water system extraction methods.

Coastal reservoirs could be used to store freshwater in coastal cities, but the conversion of coastal reservoirs to freshwater reservoirs is relatively time-consuming, and coastal reservoirs are facing a risk of salinization. Taking Zhuyu Lake as the research object, the Spatio-temporal variations of water salinity under different seasons were investigated using the field survey and modeling. The influencing factors of the water salinity of the reservoir were analyzed to discover the variation mechanism. The results showed that the disturbance of overlying water is the most significant factor affecting the salt release of sediment, and salt release was increased by 63.3% with the disturbance. The depth of the overlying water and the salt content of bottom sediment also significantly affected the release of salt, with maximum enhancement by 23.1% and 45.6%, respectively. The microbial content in the bottom mud played an essential role in maintaining the salt, and inhibiting the microbial activity could enhance the release of salt by 35.7%. Therefore, disturbing the sediment by using disturbance ships or aeration devices, and the establishment of a long-term periodic plant harvesting belt could be used in the coastal fresh reservoirs desalination and slowing down the salinization of fresh reservoirs.

该文通过采样调查汀江干流上游涂坊河流域丰、枯水文季节不同流域段底栖动物,综合分析流域内底栖动物的群落结构、优势类群、BI指数、需氧类型及生境指标等,客观反映小水电退出河段与小水电未退出河段水生态状况差异.研究结果表明:涂坊河流域已退出的石门水电站河段与仍在运行的长桥水电站河段相比,底栖动物物种数明显增加,物种多样性明显提高,高需氧种类及比例明显上升,低需氧种类及比例明显减少.经综合评价,涂坊河流域上游天然河段水环境质量为最清洁,已退出的石门水电站河段水环境质量为清洁,仍在运行的长桥水电站河段水环境质量为中度污染.

自2015年7月起,福建省展开了万里安全生态水系建设,目前此项工作已接近尾声.该文分析了福建省安全生态水系建设效果和存在问题,提出下阶段工作的建议及对策,以期有助于“十四五”期间福建省安全生态水系建设工作的开展.

通过小水电退出或转型升级,达到修复河流生态,实现经济、社会、生态效益三者统一是小水电退出政策的根本目的.该文以小水电退出后影响综合评价为总体目标,以河流水文物理特性、环境化学特性、生态特性、经济特性、社会特性为准则层,建立层级结构体系,根据群策层次分析法确定各影响因子权重,结合已退出小水电所在河段为期两年的实地调查成果和模拟计算分析成果确定评估因子分级和评分,建立量化的层次分析综合评价模型,综合评价小水电退出后影响,为后期小水电的生态修复和有序退出工作提供参考.

Seawater intrusion caused by groundwater over-exploitation is a kind of geological disaster caused by human economic activities and natural environment changes. Using freshwater recharge curtain technology is an effective means to prevent seawater intrusion. Based on the analysis of the characteristics of seawater intrusion in Pingtan island, Fujian Province, and in view of the possible seawater intrusion problems in the construction of Luyangpu underground reservoir in Pingtan Island, this paper expounds the basic principle of seawater intrusion prevention with freshwater recharge curtain, the technical measures of installing a row of recharge wells in the northern coastal zone of Luyangpu plain in Pingtan Island and using freshwater recharge curtain are put forward to prevent seawater intrusion. Through groundwater numerical simulation,the dynamic distribution of groundwater level in the north of Pingtan Island in the next 20 years is analyzed and predicted. The results show that the seawater intrusion can be effectively prevented by installing freshwater curtain recharge wells in the northern coast of Luyangpu.

该文通过物理模型试验方法模拟生态砌块挡墙在不同河道、墙后不同填料类型、不同水流作用下结构抗冲稳定变化,分析其失稳破坏机理,为生态砌块挡墙应用提供科学依据.

该文介绍邵武石壁溪河道综合治理中河道水流数值模型的应用。通过数值模型计算,求出石壁溪综合治理后河道沿程水位、流速场分布、特征断面流速、流量等变量的时空变化规律,揭示了铁路桥、弓墩桥下游、各个支流入汇处等河段的复杂流态和防冲问题,从优化水流流场角度,为石壁溪治理河道防冲方案优化提供了科学依据。