With the continuous warming of the global climate， the ecological environment and water resources in the Yangtze River Basin are apt to be affected. The analysis and study of the future precipitation change trend in the region will help to provide a theoretical basis for water resources management and ecological protection in the Yangtze River Basin. Based on the observed precipitation data and precipitation data output from 13 global climate models of the Sixth International Coupled Model Comparison Program （CMIP6） with bias correction， this paper evaluates the precipitation simulation ability of climate models in the Yangtze River Basin from 1995 to 2014.The temporal and spatial variation trends of precipitation in 2021-2040 （near term）， 2041-2070 （middle term）， and 2071-2100 （long term） are analyzed under four SSP scenarios （SSP1-2.6， SSP2-4.5， SSP3-7.0， and SSP5-8.5）.The results show that： ① The model data with bias correction can simulate the characteristics of precipitation well in the Yangtze River Basin on the spatial and temporal scale， which is close to the observed values. ②The annual precipitation in the Yangtze River Basin will increase significantly with the increase in the radiation forcing level. Compared with the historical period （1995-2014）， the annual precipitation growth in each scenario is relatively flat in the near term， and the precipitation growth is the largest in the long term. In general， seasonal precipitation shows the largest increase in winter， and the increase in spring and summer precipitation is relatively gentle. In autumn， except for the negative value of the precipitation change rate in the near term under the scenario SSP3-7.0， the other scenarios and periods are slowly increasing with lower change rates. ③Spatially， the regions with larger annual precipitation increase are concentrated on the source region of the Yangtze River and the middle and upper reaches of the Yangtze River with relatively less precipitation. The high value center of spring precipitation increase is in the source area and the north of the middle and upper reaches， while the precipitation change rate is low in the south of the basin. The precipitation increment in summer and autumn is relatively low， and the near term and middle-term precipitation in the northern part of the middle and upper reaches is lower than that in the historical period. In winter， the precipitation in the whole basin has increased， which shows that the precipitation change rate in the north of the Yangtze River Basin is the largest， and it is smaller in the south.

As one of the important flood control engineering measures， reservoirs play an important role in ensuring the sustainable growth of national economy， maintaining social stability and alleviating the contradiction between supply and demand of water resources. Meanwhile， scientific and reasonable reservoir flood control operation can effectively promote its role. In order to solve the problem of insufficient utilization of historical flood operation data， this paper proposes a new method of using random forest （RF） regression algorithm to formulate reservoir flood control operation scheme. First of all， the optimal flood operation data set is generated by optimizing the historical flood data， and the main factors affecting the reservoir discharge are determined by the RF regression algorithm. Then， the main influencing factors and discharges of the training sample flood processes are input into the RF regression algorithm to construct the discharge regression trees. Finally， the discharges of the verification sample flood processes are determined by regression trees. The example of Tianzhuang Reservoir in Shandong Province proves the operability and rationality of this method.

Promoting the green efficiency of agricultural water resources is of great significance to alleviate the contradiction between supply and demand of water resources， improve the quality of regional water environment and ensure the sustainable development of agriculture. Based on the directional distance function， the evaluation model of agricultural water resources green efficiency including unexpected pollution of non-point source output is constructed， and the spatio-temporal characteristics and driving contribution of efficiency results of 31 provinces in mainland China from 2003 to 2018 is calculated. Then fixed effect regression method is used to test the influencing factors of the green efficiency of agricultural water resources in China. The results show that： firstly， during the study period， the green efficiency of agricultural water resources in China has experienced three stages： fluctuating decline， rapid rise and rising convergence.The efficiency level of most provinces has been increased， and inter-provincial differences have been narrowed. Secondly，technological progress is the main contribution source of the variety of the green efficiency of agricultural water resources， while the driving contribution of technical efficiency variety to the change of efficiency is minor. Thirdly， supply pressure of water resources and construction level of water conservancy have significant positive correlation with the green efficiency of agricultural water resources， while the increase in water resources demand level， strength of government control and the proportion of water consuming crops in agricultural production system have inhibit the improvement of efficiency level. Based on this， the paper discusses the ways to improve the green efficiency of agricultural water resources from three aspects： simultaneously expanding the contribution of technological progress and technical efficiency， coordinating the use of market mechanism and government regulation means and improving the level of irrigation， water conservancy construction and strengthen government control.

Scientific and accurate water demand prediction results can provide a reasonable basis for urban water supply and demand balance decisions. In this paper， a combined urban water demand forecasting model is proposed by incorporating GA-BP neural networks and normal interval estimation to address the problems of many factors involved in urban water demands， small sample sizes of historical data and fluctuation and uncertainty of water demands. The results show that the relative error of the point prediction results of a single GA-BP neural networks ranges from -6.2% to 5.13%； the relative error of the interval prediction results of the combined prediction model based on GA-BP neural networks and normal interval estimation ranges from -1.01% to 0.004%， which shows that the combined prediction model based on GA-BP neural networks and normal interval estimation is more stable， more accurate and closer to the actual water demand situation in Handan. The combined model can be used as a way to forecast the water demands in Handan.

Clarifying the characteristics of heat waves and their impacts on vegetation is essential for the development of industry and agriculture and the maintenance of the ecological environment.Based on the daily average temperature data of 712 meteorological stations in China and the normalized difference vegetation index （NDVI） data， the heat wave event is defined with the excess heat factor as an indicator， and four indexes like the number of heat waves， maximum duration， frequency， and amplitude are selected. The indexes analyze the temporal and spatial characteristics of heat wave events in 8 sub-regions of China from1961 to 2017， and uses Spearman rank correlation analysis to explore the impact of heat wave events on vegetation finally.The results show that the four heat wave indexes have increased significantly and have undergone abrupt changes in the 1990s and early 21th century. The number， maximum duration and frequency of heat waves in the Qinghai-Tibet region， western region and eastern region have large mean values and changing trends over the years. The mean and changing trends of heat wave amplitude show the characteristics of spatial change of north high and south low. Heat wave events have a significant impact on the growth of vegetation. Heat wave events in the southeast coast， eastern Inner Mongolia and Xinjiang have an inhibitory effect on vegetation growth， while in the western region， Qinghai-Tibet region and southwest China heat wave events have a more obvious promotion effect on vegetation growth.

The China Meteorological Assimilation Driving Datasets（CMADS） is based on a variety of meteorological field data and meteorological station measured data， coupled to support the SWAT model-driven data set in China. The source region of the Yangtze River is located in the center of Qinghai-Tibet Plateau， the natural environment is bad， and the distribution of hydro-meteorological stations is less. Four meteorological station’s data and the CMADS data in the source region of the Yangtze River are used as driving data to verify the applicability of the CMADS data in the source region of the Yangtze River. It is found that the SWAT model has certain applicability in the source region of the Yangtze River. The Nash efficiency coefficients of the calibration and the validation period are 0.682 and 0.615 respectively. The CMADS data are poor in the source region of the Yangtze River. The Nash efficiency coefficient of the simulated runoff is only 0.447. Compared with the measured precipitation data， the quality of CMADS precipitation data in the source region of the Yangtze River is worse， but the quality of temperature data is better.

Based on the actual situation of Yiwu， this study determines 68 system variables， combined with the interactions among hydrology， society， economy and ecosystem， and fully considers the reuse of reclaimed water to build a system dynamics model. The water demand of the region from 2020 to 2050 is projected by setting 48 future economy-society-environment coupling water demand scenarios. On this basis， three combination scenarios of reclaimed water reuse are added， 144 supply and demand scenarios are analyzed， and 6 combination scenarios that are most conducive to the water security and sustainable development of regional ecological environment are selected so as to provide basis and alternative scheme sets for medium and long-term water resources planning and decision-making. The model can dynamically reflect the influence of future social and economic development on the characteristics of water use in Yiwu City， and comprehensively consider the water demand of domestic， industrial， agricultural and ecological sectors so as to provide a scientific basis for the efficient development and utilization of water resources and optimal allocation in the future.

There is a serious “sawtooth” problem in the backward inflow flow of the Three Gorges Reservoir， which affects the real-time operation of the reservoir. The data smoothing algorithm can be used to handle the error effectively. In this paper， the five-point cubic smoothing algorithm and the discrete wavelet threshold denoising algorithm are selected to study by comparing the smoothing algorithms， and compared with the three-point smoothing algorithm commonly used in practical work. The smoothing effect is evaluated by constructing the hydrological element index and smoothness index. The results show that the smoothing effect of Db7 wavelet threshold denoising is better than other wavelets in the best comprehensive application conditions of Db wavelet and Sym wavelet. Compared with the three-point smoothing method and the five-point cubic smoothing method， the Db7 wavelet threshold denoising method can fully retain the flood peak， flood volume and peak occurrence time of the original sequence， and eliminate more sawteeth of the original inflow flow.The study shows that the method of discrete wavelet threshold denoising can be used to smooth the noise of the backthrust inflow of the Three Gorges Reservoir.

Evaluating urban water security is good for finding shortcomings that constrain urban development.This paper introduces the information substitutability index selection method to refine the index system， reducing the 24 indicators to 10 indicators， and using constant weights to check the index system before and after selection. Constant weight modified by the idea of variable weight， and the model is validated with Xi’an City as an example. The results show that the urban water safety level in Xi’an increases year after year and finally stabilizes at level II. The shortcomings are the amount of water resources per capita， the amount of groundwater recharge， the proportion of secondary industry， and the effective irrigation area. There is no change in water security level before and after index selection. After simplifying the index system， the method of information substitutability index selection can retain much of the information of the original index system.The method of variable weight can more realistically reflect the role played by each indicator in different states.Compared to the method of constant weight， the method of variable weight shows greater variability.

To explore the characteristics of the evolution of water resources in the Yellow River Basin， information entropy， CEEMDAN， and Copula theories are used to study the temporal and spatial evolution of precipitation in the Yellow River Basin from 1960 to 2017. It is found that， ① In the past 50 years， the precipitation in the Yellow River Basin as a whole has shown a downward trend， but the precipitation in the source area is increasing slowly； ②After 2002， the Spatiotemporal information entropy of precipitation in the Yellow River Basin declined and complexity decreased. ③CEEMDAN decomposition results show that the observation and research on precipitation in the Yellow River Basin should be mainly focused on the short cycle of 2~4 years， RES balance reflects the overall decline of precipitation sequence but gradually recovered in recent years； ④Through the Gumbel-Copula function， it is found that the combined distribution of annual and flood season precipitation in the Yellow River Basin at different stages is mainly abundant and dry， and the probability of synchronization increases after the mutation. This paper studies the spatiotemporal characteristics of precipitation in the Yellow River Basin at different stages， which helps to further understand and grasp the characteristics of the water circulation in the Yellow River Basin， and then provide support for the ecological protection and high-quality development of the Yellow River Basin.

Studying the carrying capacity of regional water resources is an important guarantee for realizing regional sustainable development. Taking the Beijing-Tianjin-Hebei region as the research object， this paper selects 16 evaluation indicators and divides the indicators into four sub-systems： society-economy-ecology-water resources from the perspective of the system. Then according to the principle of minimum information entropy， the entropy method， CRITIC method and mutation， the weights determined by the coefficient method are coupled， and the objective function is constructed to find the optimal combination weights through the genetic algorithm and calculate the comprehensive score. On this basis， the BP neural network is used to train the model and predict the future trend of the Beijing-Tianjin-Hebei water resources carrying capacity. The results show that the water resources carrying capacity of the Beijing-Tianjin-Hebei region was initially at a low level but there was an upward trend， the mid-term jitter declined at a low level， and showed an upward trend in recent years. It is predicted that the water resources carrying capacity of the Beijing-Tianjin-Hebei Region will be at a high level and reach a steady state.

Water resources safety is the basis and premise of social and economic security and sustainable development. Under the increasingly urgent situation of water resources problem， it has become the focus of attention from all walks of life. The commonly used water resources security evaluation index is sorted out， and the basic index database of water resources security evaluation is established. Considering the connotation of water resources safety， four criteria are set up， including water supply guarantee， water resources development， water resources allocation and water resources utilization， then a comprehensive evaluation index system consisting of 11 evaluation factors is constructed．According to the data of natural， economic， social and water resources in Linyi City from 2013 to 2018， the comprehensive evaluation of water resources security in Linyi City is carried out by using the analytic hierarchy process. The results show that the overall level of water resources security in Linyi City is in a good state， but there is a certain demand for water resources security in water resources development and allocation.

In this paper， the Lightweight Gradient Boosting Tree Model （LGB） is employed to simulate and forecast monthly runoff sequences of the Three Gorges Reservoir， and the forecasting uncertainties are analyzed by using the Hydrological Uncertainty Processor （HUP）. The findings of this paper are as follows： ① the comparison between predictions of GBDT and LGB models indicates that the LGB model has higher accuracy than the GBDT model for both calibration and validation periods； ② the preferred forecasts （Q50 values） generated by the HUP model present a higher accuracy than the deterministic prediction generated by the LGB model， especially for the flood season； ③ the 90% uncertainty confidence interval with a narrow bandwidth for both calibration and validation periods can cover most observed points， which suggests that the result of uncertainty analysis is accurate and reasonable.

In order to reveal the variation law and driving factors of runoff and sediments in the upper reaches of the Yellow River， according to the time series data of three representative hydrological stations in the upper reaches of the Yellow River， average difference T methods， double cumulative curve method， wavelet analysis， cumulative slope rate change rate method and other methods are used to analyze and study the characteristics of runoff and sediment change in the upper reaches of the Yellow River. The results show that the runoff and sediment discharge of the three representative stations in the upper reaches of the Yellow River showed a decreasing trend from 1960 to 2019. The annual runoff at Tangnaihai Station， Lanzhou Station and Toudaoguai Station in the upper reaches of the Yellow River havean abrupt change in 1989， 1985 and 1985， and the annual sediment load of the three stations abrupt change in 1989， 1999 and 1985. Wavelet analysis is used to find that runoff has a main cycle of 9~16 a， and sediment discharge has a main cycle of 11~16 a. The cumulative sediment reduction of the three stations in the upper reaches of the Yellow River is about 107 million t，1.1 billion t and 1.639 billion t， respectively， and the sediment reduction increased along the river. The variation law of runoff and sediment is influenced by precipitation and human activities， and human activities play an important role in the variation of water and sediment.

Slow water bodies， mainly represented by landscape lakes and ecological wetlands， are becoming more and more important in urban construction. How to increase water exchange areas and slow down the deterioration of water quality is an important problem we are faced with. Based on particle image velocimetry （PIV） technique， the effects of spacing ratio， diversion flow rate and shape of double bluff body （islands） on two-dimensional flow field distribution， water displacement rate and average velocity of the flow field in slow water are studied. The experimental results show that the diversion flow rate is the main controlling factor for the intensity of the flow field in the slow water， and the hydrodynamic exchange efficiency and the average velocity of the water flow are proportional to the diversion flow. The bluff body can obviously improve the range of flow movement and increase the fluidity of water. It is found that the fluidity of the flume water is the strongest and the displacement rate is the highest when the prism and cylinder are disturbed together. The maximum displacement rate reaches 72.89% when Q=6.8 L/min and G/D=6. The experimental results will provide some reference for optimizing the layout of islands in the landscape lake.

The raw water of R reservoir with Microcystis as the dominant algae and the raw water of J reservoir with Cylindrospermopsis rackiborskii as the dominant algae are taken as the research objects， and the preoxidation coagulation processes are tested respectively. Chlorine dioxide and sodium hypochlorite are used as pre-oxidants， and the mass concentration ratios of 0∶1，1∶1 and 2∶1 are combined with aluminum sulfate coagulant to analyze the removal effect of pre-oxidation coagulation on algae and organic matter， and an appropriate pre-oxidation dosing strategy is established. The results showed that all the three combinations could improve the effect of algae coagulation. For raw water in R reservoir， chlorine dioxide and sodium hypochlorite are not recommended for pre-oxidation. The raw water of J reservoir using chlorine dioxide and sodium hypochlorite is better than that using sodium hypochlorite alone to remove algae and organic matter.

In order to analyze the influence of the uncertainty of hydrogeological parameters on the output of the groundwater numerical simulation model， this paper studies a hypothetical example. First， a groundwater numerical simulation model is established. Then sensitivity analysis is used to screen out the parameters that have a greater impact on the output of the simulation model. As a random variable， in order to reduce the computational load caused by repeatedly calling the simulation model， the Kriging method and the BP neural network method are used to establish the replacement model of the simulation model and the accuracy levels of the two are compared， and the BP neural network replacement model with higher accuracy is selected to perform Monte Carlo simulation. Among them， when the BP neural network method is used to establish the replacement model， the third-point algorithm is used to quickly determine the number of hidden layer nodes that minimize the error of the replacement model. Finally， the results of the random simulation are statistically analyzed and the interval estimation and evaluation of the risk of groundwater pollution are compared. The results show that when the confidence level is 90%， the confidence intervals for the concentration of the three observation wells are 367.48~415.67， 205.12~230.33 and 118.85~132.82 mg/L. Combined with the risk assessment， it is calculated that the risk of groundwater pollution in observation wells No.1， No.2 and No.3 in the study area are 0.66， 0.60， and 0.58， which provides a scientific basis for groundwater pollution prevention and control.

An increasing and wide attention has been paid to the effect of artificial reservoirs on river geomorphology， water ecological environment system and hydrological characteristics. In this paper， two reservoirs on the Shiguan River， a tributary of the Huaihe River Basin， Meishan Reservoir and Nianyushan Reservoir are used as the study area. Samples are taken from the water body of the reservoirs， the Jiangjiaji section in the downstream of the reservoir， the Wangjiaba and Runheji sections at the upstream and downstream sections of the main stream of the Huaihe River in December 2020 to analyze the spatiotemporal variation characteristics of hydrochemistry ion， electrical conductivity， hydrogen and oxygen isotope content， and discuss the impact of reservoir construction on the water cycle of the basin. The results show that the two isotopic compositions of the water body have the same trend along the river direction， and the overall trend is positive. One is the dam interception and the other is the influence of latitude effect. The temporal change of isotopic concentration of the water bodies in the Meishan Reservoir and Nianyushan Reservoir is relatively stable， the isotopic temporal change of the upstream Wangjiaba Station is relatively stable， and that of the two sections on the tributary and the main stream affected by the reservoir fluctuates greatly. Hydrogen and oxygen isotopic composition of the river and the reservoir deviates from the local atmospheric precipitation line， mainly due to the interception effect of the reservoir， so that the evaporation is stronger than that of the ordinary river. The lower reaches of Jiangjiaji and Runheji Cl^- and the electrical conductivity are affected by the water discharge from the reservoir， the value of which decreases. Jiangjiaji is closer to the reservoir and has a greater impact.

The Qinghai-Tibet Plateau （QTP） is an important ecological barrier in China. In recent years， the large-scale conversion and reclamation of farmland in the QTP are bound to weaken or induce soil erosion. To explore the impact of different land-use change patterns on soil erosion in the QTP， taking the farming area of the QTP as an example， based on the CSLE model， the soil erosion status of the farming area in 2015 is analyzed， and the comprehensive index of soil erosion intensity change and the contribution of erosion reduction is proposed for the first time. The concept and calculation formula is used to quantify the impact of cultivated land changes on soil erosion and analyze the contribution of different cultivated land change patterns to soil erosion reduction. The results show that： ① The average soil erosion module in the farming areas of the QTP in 2015 is 195.6 t/（hm²·a）， and the potential annual soil loss is approximately \mathrm{446.51} \times {\mathrm{10}}^{\mathrm{6}} \text{?} \mathrm{t} / \mathrm{a}. ② The composite index of variation in soil erosion intensity in returning farmland to forest， back tillage to grass， and unused land-to-farmland are -378.24， -118.54 and -5.44 t/（hm²·a）， and the effect of reducing soil erosion decreases in turn， while the composite index of variation in soil erosion intensity in grassland and forest land reclamation as cultivated land， and farmland that degrades into unused land are 16.53， 32.34 and 200.61 t/（hm²·a）， the effect of increasing soil erosion increased in turn. ③ Land-use changes in 2000-2015 reduced soil erosion intensity by 245.54 t/（hm²·a） in the agricultural areas of the QTP with a decrease of 55.66% compared to the unchanging land-use scenario. Under the dual influence of soil erosion intensity change comprehensive index and area， the order of contribution of different land-use changes to soil erosion reduction is： returning farmland to grassland > returning farmland to forest > conversion of unused land to cultivated land >conversion of woodland to cultivated land > conversion of cultivated land to unused land > conversion of grassland to cultivated land. The research results provide a reference for the sustainable development and utilization of water and soil resources and ecological environmental protection in the agricultural areas of the QTP.

The outbreak of algal bloom is a process of phytoplankton proliferation and aggregation under suitable hydrological， meteorological and nutrient conditions. Further exploration of the correlation between algal bloom and the corresponding environmental factors can provide a basis for risk warnings of algal bloom. Based on the nearly two-year monitoring data of hydrology， meteorology， water quality and water ecology of the Mianhuatan Reservoir in Longyan City of Fujian Province， the succession characteristics of phytoplankton community are analyzed in this paper. Meanwhile， the LSTM artificial neural network model is established to forecast the algal bloom. The results show that 6 phyla and 63 genera were found in the Mianhuatan Reservoir， and the main dominant species were cyclotella， synedra， chlorella and chlamydomonas. When the daily average temperature， water temperature， wind direction and inflow flow are used as input variables， the monitoring method is not only the simplest but also the best result. The fitting coefficient between the predicted value and the measured value has reached 0.76. The relative error is in the range of 0.02~0.73 in the high-risk period， which shows the stability of the model is acceptable. The model is expected to be used for risk warning of algal bloom in Mianhuatan Reservoir and provides a means for optimizing local water resources management.

Batch experiment is conducted to investigate the influences of Si application （0， 100， and 200 kg SiO₂/hm²， abbreviated as S₁ and S₂） on the isothermal adsorption of ammonium nitrogen in soils contaminated by Cd （2.5 and 5 mg Cd/kg CdBr₂， Cd_2.5 and Cd₅ for short ） . After that， five models including linear model， Freundlich model， Langmuir model etc. are used to fit the experiment data. The results show that ① the adsorption of NH₄ ⁺ decreases with the increasing Cd content due to the competitive adsorption between Cd²⁺ and NH₄ ⁺ in soil， which implies that the heavy metal pollution might increase the risk of non-point source pollution； ② the addition of exogenous silicon significantly improves the adsorption capacity and adsorption rate of NH₄ ⁺ in the following order：Cd₅<Cd_2.5<CK<Cd₅S₁<Cd₅S₂<Cd_2.5S₁<Cd_2.5S₂； ③ the experiment data can be simulated by all the six models among which Langmuir model has the best fit with the R ² ranging from 0.948 6 to 0.996 3， indicating that Langmuir model can better describe the influence of silicon application on the adsorption of NH₄ ⁺ in the Cd contaminated soil. Silicon application can effectively improve the adsorption capacity of NH₄ ⁺in the Cd contaminated soil and reduce the loss of nitrogen fertilizer， which is significant to the cooperative governance of heavy metal pollution and non-point source pollution.

The quantity of rubble revetment works is huge and the dynamic characteristics are prominent in the rapidly changing area of the Yangtze River. It is of great significance to study the change of flow conditions in the river reach to evaluate the implementation effect of the project and analyze the influence of river regime change. In this paper， based on Delft3D software， the influence of the rubble revetment project on the water level， flow velocity and diversion ratio of the nearby reach is studied by using the planar two-dimensional flow mathematical model. The results show that after the implementation of the project， the variation range of water level is generally within 0.01 m， and the variation range of water level at the low-water slack is slightly higher than that at the high-water slack. The flow in the river is affected by runoff and presents a relatively regular water level change situation. The flow velocity changes are mainly concentrated on the rubble-throwing engineering area， regardless of the rising hour or the falling hour， and the maximum amplitude of the flow velocity is about 0.3 m/s， which mainly shows the law that the flow velocity in the rubble-throwing area decreases and the flow velocity in the deep groove increases. The implementation of the project impedes the flow of Liuhaisha Channel and reduces its diversion ratio. The diversion ratio of Rugao middle branch and Rugao left branch increases， and the influence of the project on the flood tide is greater than that of the ebb tide. The results can provide reference for the Yangtze River Channel management and planning.

A water source vulnerability assessment index system based on the driving force-pressure-state- impact-response-management （DPSIRM） model is established， comprehensively considering the economy， society， resources， environment， ecology and other influencing factors of urban water resources in plateau basins. The entropy method is used to weight each evaluation index， and the set pair analysis and obstacle degree model is used to evaluate the water resources vulnerability of the Yunlong Reservoir water resources in Kunming from 2014 to 2019.The results show that the vulnerability of Yunlong Reservoir’s water resource was strongly vulnerable in 2014， and moderately vulnerable from 2015 to 2019. The confidence value of its middle-level vulnerability has been increasing year by year， and the vulnerability of water resources has gradually decreased， indicating that the implemented water resources management policies have achieved results. Judging from the diagnosis results of the obstacles in the various subsystems of the evaluation model， the pressure， status， and influence subsystems’ obstacles played a dominant role from 2014 to 2015， the influence and response subsystem played a leading role from 2016 to 2018， and the pressure and influence subsystem played a leading role in 2019， and subsystem obstacles have a greater impact. It is suggested that the sound development of water resources security should be promoted from the perspective of the system theory， the water quality management and control of water source areas should be strengthened， and the comprehensive development and governance of water resources should be strengthened.

The long-term trends of reference evapotranspiration （ET ₀） and the main caused in Dianxi Plain were studied in this paper， which provides the basis for dealing with the impact of climate change on agriculture and water resources planning and management. The daily ET ₀ during 1955-2018 was calculated by using the Penman-Monteith formula recommended by FAO， the variation regularity of ET ₀ and radiation term （ET_rad ） and aerodynamics term （ET_aero ） were analyzed. The trends of mean temperature， humidity， sunshine and wind speed， which are the main driving factors of ET ₀ were analyzed by using the Mann-Kendall method. The relationship between ET ₀ and main driving factors was obtained by partial correlation analysis. The results show that ET ₀ decreases obviously in 1955-2018， its decline rate is -19.5 mm/10 a. The average annual ET ₀ is 1 070.5 mm. The annual average ET_rad and ET_aero as the percentage of ET ₀ is 61.2% and 38.8% respectively. The annual average daily ET ₀ shows a single peak curve and its average value is 2.9 mm/d. ET _rad accounted for 53.0%~80.2% is dominated from April to October， while ET _aero accounted for a larger proportion in other periods. The average temperature shows a significant upward trend； its decline rate is 0.23℃/10a. The sunshine， average wind speed， relative humidity all show an obvious downward trend in Dianxi Plain， the decline rates are -138.85 h/10 a， -0.09 m/s/10 a and -0.58/10 a respectively. ET ₀ is linearly positively correlated with the average temperature， sunshine hours， and average wind speed and the correlation coefficients are 0.909， 0.608， and 0.534， respectively. ET ₀ is linearly negative with relative humidity， and the correlation coefficient is -0.371. It is mainly due to the significant decrease of sunshine and wind speed that ET ₀ shows a significant downward trend in Dianxi Plain.

The variation of volute section area has an important influence on the hydraulic performance of centrifugal pump. The influence of five kinds of volute section area on pump performance was studied by CFD numerical simulation. The results show that the N-type model has the best hydraulic performance and the U-type model has the worst hydraulic performance，the difference in head and efficiency is 5.01% and 9.47%，respectively.Slowing down the area change speed of the latter two sections can effectively reduce the low velocity area of the tongue and the diffusion section. Under off design condition， the influence of volute area on pressure fluctuation decreases with the increase of flow rate； The main frequency of pressure fluctuation of U-type， inverted S-type and linear models all appears at the blade frequency. The main frequency of pressure fluctuation of N-type and S-type models appears at the blade frequency under the design condition， and it is lower than the shaft frequency under the off design condition. The overall pressure fluctuation of N-type and S-type models is small.Under off design condition， the amplitude of pressure fluctuation increases at the main frequency of each model， which is greatly affected by the change of volute area. On the whole， the spiral case with good hydraulic performance should conform to the law that the area of spiral section tail increases slowly and the area of spiral section front half increases appropriately.

Good water and fertilizer regulation mode is conducive to the exchange of nutrients elements between soil and crops， which is one of the important factors for high yield of rice. In order to explore the mechanism of the effect of slow-release fertilizer on paddy soil， fertility root dry weight and yield under alternate wetting and drying irrigation conditions， pit test of rice planting was carried out in Hubei Irrigation Experiment Center Station from May to September 2019. Plant height， chlorophyll SPAD value， tiller number and soil samples were collected under the interaction of flooding irrigation （W1， CF）， alternate wetting and drying irrigation （W2， AWD） coupled with traditional fertilizer （N1） and slow-release fertilizer （N2） to analyze the nitrogen and phosphorus content， yield and root dry weight at yellow ripe stage. The results show that the total nitrogen of upper layer （0~20 cm） and lower layer （20~40 cm） of AWD is 2.2%~78.63% higher than that of CF， the total phosphorus of upper layer is 64.27%~162.86% higher than that of CF， and the total phosphorus of lower layer is 30.80%~43.52% lower than that of CF. The total nitrogen in the upper and lower layers of slow-release fertilizer is 5.06%~79.95% lower than that of traditional fertilizer. Total nitrogen in lower soil is significantly different under different fertilizer types， and total phosphorus in upper soil is highly significant under different fertilizer types. Slow-release fertilizer significantly improves the dry weight of roots. AWD and slow-release fertilizer （W2N2 ） has the highest yield of 10 505 kg/hm²， AWD and slow-release fertilizer （W2N2） is 8.53% higher than that of lowest control treatment CF and traditional fertilizer （W1N1）.

The study is carried out on the loess surface of the Wangdonggou sub-basin in the loess tableland region， combining field sample collection and indoor and outdoor laboratory analysis to investigate the spatial and temporal response of soil moisture and soil water-hydrogen-oxygen stable isotopes to secondary rainfall events under different land use patterns， with the aim of identifying the mechanism of soil moisture infiltration and redistribution in the loess tableland region， and providing scientific and technological support for the optimization of agricultural production patterns and ecological restoration in the loess plateau region. The results show that ① before and 7 days after the rainfall event （47.6 mm）， the average soil moisture content in the range of 0~3 m is 16.13% ± 1.23%， 16.01% ± 1.38% and 16.53% ± 1.43% in the barren grass， apple and maize fields， respectively. The maximum depth of soil moisture response to this rainfall event is in the order of maize field， apple field and barren grass field， with the first two having a lag in response. Soil moisture is classified into active， weakly active and relatively stable zones by using ordered cluster analysis， with the depth ranges of 0~0.2， 0.2~0.4 and 0.4~3 m in the barren grassland， and 0~0.2， 0.2~0.6 and 0.6~3 m in the apple and maize fields respectively. ③Under this rainfall event， the rainfall δ²H and δ¹⁸O are -81.30‰ and -11.12‰ respectively. The infiltration capacity of the soil surface layer after rainfall is in the order of apple field > maize field > maize field； the stable isotopes of soil water hydrogen and oxygen in the 0~3 m soil layer shows alternating processes of “piston flow” and “preferential flow” for rainwater infiltration.

Based on CFX software， N-S equation and RNG k-ε turbulence model were used to simulate theflow pattern of the forebay of a pumping station. To analyze the flow pattern of the forebay without rectification， and study the influence of the position， length and bifurcation angle of the V-shaped diversion pier on the flow pattern of the forebay and the uniformity of axial velocity distribution at the inlet of the unit. The results show that the laminar flow pattern of the forebay surface of the pumping station is better without rectifying measures， and there is a large area of the backflow on both sides of the bottom. V-shaped diversion pier have good diversion and diffusion effect on the incoming flow， but a single V-shaped diversion pier scheme is difficult to improve the uniformity of axial velocity distribution of each unit. The setting of two identical V-shaped diversion piers often leads to the deviation of the water flow in front of the No.1 unit， resulting in the poor inflow state. Setting two different V-shaped diversion piers is more beneficial to the elimination of the bad flow pattern in forebay. When pier A and pier B are respectively 15D and 20D away from the inlet of the inlet pool， 7.5D and 5D away from the centerline of Unit No.2， the lengths are both 3D， and the bifurcation angles are respectively 15° and 30°， the backflow area on both sides of the front pool has A better improving effect. The uniformity of axial velocity distribution at the inlet of No.1， No.2 and No.3 units increases by 17.8%， 2.7% and 9.8%， respectively.

In order to reduce the axial force of the semi-open centrifugal pump with low specific speed， the influencing factors of the axial force of the semi-open centrifugal pump are analyzed and studied by means of orthogonal experiment by combining numerical analysis. The blade tip clearance and balance hole diameter are selected as experimental factors， and each factor takes 5 levels to carry out orthogonal design. SST k-ωTurbulence equation is used to calculate the axial force of the semi-open centrifugal pump. According to the comparison between the calculated results and the experimental results of the original model， it is found that the head and efficiency change within 5%， so the numerical simulation method is feasible. Based on L₂₅（5 ²） orthogonal table， 25 groups of experimental schemes are designed， and the optimal scheme is obtained by analyzing the numerical simulation results of 25 groups of experimental schemes. The results show that by reducing the tip clearance and establishing the balance hole， the back cavity pressure increases significantly， and the axial force of the centrifugal pump decreases greatly， the maximum reduction is 440.59 N， accounting for 45.6% of the total axial force of the original model. At the same time， it has little effect on pump performance， efficiency only reduces by 3.76%， and the head reduces by only 0.3%.

In recent years， with the issuance of the total water consumption statistics scheme （for trial implementation） and the water consumption statistical investigation system， the statistical investigation of agricultural water consumption in China has become increasingly standardized， and the scientificity and rationality of statistical methods have been further improved. The scope of the report has continued to expand， and the reporting platform has also been continuously improved. However， since the “Statistical Investigation System for Water Use” is still in the initial trial stage， there are still many problems in the implementation process， which need to be further studied in the next step.

The scaling effect has significant influences on the stress deformation feature and dilatancy characteristics of rockfill materials. Many understandings on the scaling law have been detected， while the underlying mechanism is still unclear. In order to further reveal the mechanism of scaling effect of rockfill material， the numerical triaxial tests of rockfill materials with different sizes are carried out based on the crushable discrete element method （DEM）. The results show that the larger the sample size is， the lower the shear strength is and the stronger the shear shrinkage is， and this phenomenon is more significant with increasing confining pressure. The initial load-bearing structures of the specimens generated by similar grading method are similar， while the load-bearing structures will become thinner with increasing sample size. In addition， the reduction of the effective coordination number distribution of each particle size group decreases with an increasing sample size， and this phenomenon becomes more obvious with larger confining pressure. The evolution of the effective coordination number distribution of each particle size group is positively correlated with the particle breakage rate. The higher the particle breakage rate is， the higher the effective coordination number distribution of each particle size group is. It is found that the differences in the evolution of effective coordination number distribution difference among different size groups of rockfill specimens is one of the meso-mechanism of the scaling law of dilatancy characteristics.

In order to explore the contradictory relationship between power generation and ecological benefits of Qiao-qi Hydropower Station， this paper establishes a reservoir multi-objective optimization operation model with the goal of maximizing the annual power generation and average ecological flow of Qiao-qi Hydropower Station according to the ecological flow discharge methods of different time scales. The model is based on the platEMOopen source toolbox of MATLAB， and runs the ecological water release model generated by the Tennant method based on the annual and monthly flow processes， and analyzes the benefits of power generation in the two modes. The results indicate that when the ecological flow is 20%~30% of the average flow for many years， the Pareto surface of the two goals of ecological flow and annual power generation shows an approximately linear trend； the optimal power generation is obtained under the same leakage as the actual ecological flow. The amount of electricity is 836 million kWh， which increases by 21 million kWh compared to the actual power generation of the year； the ecological water release model based on the annual scale has more power generation benefits than the ecological water release model based on the monthly flow process.

This paper aims to analyze the reliability of the deflection of the main beam of the plane gate more reasonably， and solve the problem of the inability to obtain an accurate probability distribution of the hydrostatic pressure of the gate due to the insufficient statistical data of the acting water head of the gate， interval analysis can be performed on the limited gate acting water head data， and its mean value and standard deviation can be expressed in interval quantities， that is， the interval parameter of the hydrostatic pressure of the gate can be obtained. By taking a plane submerged gate in Danjiangkou Reservoir as an example， the reliability results of the deflection of the main girder of the gate are calculated by using interval parameters and traditional parameters. It can be seen that the results obtained by using interval parameters include the deflection reliability index of the gate main girder using traditional parameters， and can give the confidence that the true value of the gate girder deflection reliability index falls within the range of the obtained interval. Intervalization of the statistical parameters of the hydrostatic pressure of the gate can well solve the problem of insufficient statistical data of the hydraulic head of the gate.

The bottom outlets of many high dams adopt deep-water short-hole pressurized inlet type， choose eccentric hinge arc door and corresponding sudden expansion and sudden fall articulation arrangement. As sudden expansion and fall can abrupt change in body shape， complex water flow conditions， its hydraulic characteristics are important factors affecting the safe operation of the bottom hole. It is concluded that the bottom hole flow coefficient is in the range of 0.88~0.9， the water pulsation is strongest at the bottom plate of the sudden expansion and drop jet impact， the maximum pulsation pressure can reach 1.4 times of the water impact force， the size of the bottom hole of this body type increases from 1m to 1.2 m， the ventilation hole area increases by 25%， the concentration of gas doping in the water flow of the drainage channel is obviously increases， and the minimum gas doping concentration is more than 3% as specified in specification. The results can have some reference significance for the gas doping and corrosion reduction of similar projects as well as design and construction.

Considering irrigation， flood control， ecology and power generation， a multi-objective joint optimal operation model was established in this study. Maximizing power generation benefit of cascade hydropower stations was selected as the optimization objective， the agricultural irrigation， ecological flow and flood control objectives were transformed into solid constraints， and the improved differential evolution algorithm is used to solve the model. This paper introduced the scaling coefficient of irrigation water plan， analyzed the competition relationship and replacement rate between irrigation and power generation objectives through multi-scenario simulation， and revealed the benefit replacement mechanism between multiple objectives and the gain mechanism of joint optimal operation of hydropower stations. The results show that： ① Compared with the actual operation， the total power generation and benefit increase by 4.32% and 4.30% respectively. ② An obvious competitive relationship exists between the total power generation and irrigation water supply， and the replacement rate is 0.0845 kWh/m³； ③ With the decrease of the scaling coefficient， the adjustment of the joint optimal operation strategy realizes the maximum overall benefits of the cascade through the replacement of water volume and water head between upstream and downstream power stations.

J₁b^1-4-2 layer of sandstone has been exposed on the spillway right side slope of Tuoying Reservoir， which have deep weathering at the folds，the rock mass is broken， the muddy interlayers developed.Due to the influence of bad geological conditions， the stability problem of the slope during the construction period is prominent. Based on the geological conditions exposed by the spillway excavation， this paper analyzes the existing deformation and support status of the slope， and uses FLAC3D software to evaluate the stability of the constructed excavation and support scheme， and then proposes two reinforced support schemes to calculate and compare， which provides a design basis for the slope reinforced support practice. Based on the numerical simulation results， the broken sandstone layer J₁b^1-4-2 has a certain impact on the displacement field of the spillway right side slope， and the deformation of the pile number 0+067 m~0+129 m is relatively large. Under the constructed excavation and support scheme， the maximum Y-direction displacement of the slope reaches 17.437 mm. Compared with the anchor cable reinforced support scheme， the Y-direction maximum displacement value and the larger deformation area of the slope after the anchor cable and anchor pile reinforced support scheme is significantly reduced， and the supporting effect is more ideal. Using the anchor cable and anchor pile reinforced support scheme is recommended.

With large-scale wind energy， solar energy and other new energy access to electricity， the randomness and intermittence bring great pressure to power grid dispatching and real-time balance. Pumped storage power station will play a more important role in ensuring the safe and stable operation of power grid and improving the quality of power supply. Equipment maintenance is a necessary measure to ensure the healthy operation of pumped storage units. A digital maintenance technology integrating virtual reality， intelligent decision and multiple information is proposed. A digital management system for unit maintenance of pumped storage power station is developed. The system structure and three key technologies including maintenance planning， maintenance implementation and maintenance control are introduced. Based on engineering practices， four functional modules of the system： maintenance panorama， maintenance planning， maintenance implementation， maintenance evaluation are displayed. Functions such as maintenance knowledge base construction， fine modeling， operation deduction， standardized operation， schedule control and resource prediction have been realized. Practical application shows that the system can effectively guide the maintenance of the unit， improve the quality and efficiency of maintenance operation， and save costs. The intelligent development of unit maintenance of pumped storage stations in China can also be promoted.