A similar basin identification method was proposed to improve the reliability of similar basin identification for hydrological forecasting in ungauged basin. The method introduced the basin time-varying feature information and constructed a time-varying feature matrix (TVFM). A dimension reduction method for the TVFM was proposed to obtain the basin feature vector. The classical K-means clustering method was adopted to implement the identification of the similar basins. Seventeen natural catchments in Jiangxi Province were selected and the Xin'anjiang model was applied in this research. A series of studies were carried out which includes feature vector and feature matrix construction, similar basin identification, parameter transfer, and comparison & analysis of hydrological forecasting results. The following conclusions can be drawn. The proposed TVFM can achieve better forecasting results in ungauged basins. Compared with the traditional similar basin identification method based on time-invariant underlying surface information, the prediction accuracy is improved. The similar basin identification based on time-varying comprehensive features generates the best predictions, and the prediction accuracy based on time-varying meteorological features is better than that based only on time-invariant underlying surface features. Comparison with the single factor methods, the directional problem of the parameter transfer can be partially solved by the proposed comprehensive method. Unfortunately, the directional problem cannot be completely overcame until recently.

The power imbalance between DC side and AC side of single-phase grid-connected photovoltaic inverter leads to double frequency power pulsation on DC side. The additional active power decoupling circuit can effectively suppress the secondary ripple, but due to the additional components, the system efficiency of single-phase inverter will be reduced. Aiming at the above problems, this paper proposes a control strategy based on Buck converter that can reduce the power loss of decoupling circuit. By calculating the power loss of the decoupling circuit and analyzing the working constraints, the relationship between the power loss and the average voltage of the decoupling capacitor was obtained, and then a control strategy to directly control the average voltage of the decoupling capacitor was proposed. Simulation results show that the proposed control strategy can effectively suppress the DC side voltage ripple and reduce the power loss of the decoupled circuit.

To study the internal flow characteristics of bulb tubular turbine with different blade opening structures under large medium and small flow conditions, and to make theoretical support for the optimization of the flow passage components structure and the coordinated relationship, the research indexes were taken as three-dimensional streamline distribution, central meridian plane streamline distribution and central meridian plane pressure distribution. The results indicated that the maximum flow velocity existed at the runner of the bulb tubular turbine in the flow pattern analysis, and the flow pattern was chaotic, which was the focus of efficiency optimization. The reason of vortex in the draft tube was analyzed, and it could be optimized by reducing the dead water area. The internal pressure showed an overall decline tendency from the inlet channel to the draft tube. The pressure value at the runner discharge cone was the smallest. The pressure in the draft tube gradually increased along the flow direction, and the highest pressure value was 82 464.15 Pa when the flow rate reached 124.92 m³/s. The calculation results can provide a reference basis for the modification and optimization of the bulb tubular turbine.

Since total organic carbon (TOC) is not a routine hydrological monitoring data, the monitoring frequency is much lower than that of flow data and it often has missing values, which makes it difficult to evaluate TOC flux. This study proposes an improved computational model based on functional data analysis (FDA) for the evaluation of riverine TOC fluxes. First, the discrete data set is functionalized, and all the indicators are transformed into s function curves in the same evaluation time domain. And then the TOC flux of the evaluation section during the study period is calculated by Riemann integral. The results of the TOC evaluation at the Zhutuo station on the Yangtze River show that, The average value of the annual TOC flux at Zhutuo Station from 2018 to 2020 is 702 000 t; The intra-annual distribution of TOC fluxes is extremely uneven, with a high concentration in the flood season, especially in summer; The annual average value of TOC flux during the flood season (June to September) is 438 200 t, equivalent to 62.43% of the total; The annual average TOC flux in summer is 349 000 t, equivalent to 49.72% of the total; While the annual average value of TOC flux during the dry season (October to May) is 263 700 t, equivalent to 37.57% of the total; The annual average TOC flux in winter is 71 300 t, equivalent to 10.15% of the total; Compared with the traditional method, the improved TOC flux model is also able to deal with missing values and inconsistencies in multi-indicator monitoring sequences more effectively, and to accurately assess the course of TOC fluxes over different seasons and periods of abundance and depletion.

To further promote the construction of sponge cities, system dynamics and Morris, EFAST sensitivity analysis methods were used to analyze the regional differences in the benefits of sponge facilities in residential areas. The research conclusions are as follows: The comprehensive incremental cost benefit and economic, environmental, and incremental social benefits of Shenzhen, Beijing, Lanzhou sponge facilities in operation for 20 years accounted for 1 504.5 (69%, 23%, 8%), 352.4 (54%, 28%, 18%), and 2.0 (27%, 53%, 20%) ten thousand yuan, respectively. The sensitivity of the comprehensive benefit parameters of sponge facilities from high to low is sorted as average annual precipitation, rainwater recovery rate, economic loss caused by water shortage, etc. Among them, the rainfall and rainfall characteristics limit the benefit value of Beijing and Lanzhou. The low of water use in Lanzhou also affects the benefit value.

Reservoir operation rules, as an important tool to guide reservoir operation, are not only the decision-making reference in the reservoir planning and design period, but also one of the key technologies affecting the comprehensive benefits of the reservoir in the operation and management period. Therefore, based on the historical operation data of reservoirs in the upper reaches of the Yangtze River, the number of periods, early water level, inflow, outflow and current inflow were selected as the influence factors to form the input factor set combined with the reservoir operation principle and operation characteristics. Comprehensively considering the characteristics of operation data and the principle of decision tree, the end of period water level was determined as the model output and then the corresponding simulated water level evaluation index was proposed based on the reservoir regulation capacity. The correlation coefficient and mutual information were used as the correlation evaluation index of model input factors, and the tree Parzen evaluator was introduced to optimize the number of input factors and algorithm super parameters. Finally, the reservoir operation rule extraction model based on decision tree and its integrated model was established and the reservoir operation rule integrating historical operation process and expert experience was formed. The experimental results show that the decision tree and its integrated model have strong ability and applicability in the extraction and application of reservoir operation rules.

The paper aims to comprehensively grasp the carrying capacity of water and soil resources in Ningxia, and promotes the coordinated development of water and soil resources in arid and semi-arid areas. An evaluation index system was constructed based on DPSIR model. The CRITIC-entropy weight-TOPSIS was applied to evaluate the carrying capacity of water and soil resources in Ningxia from 2012 to 2019. The obstacle degree model and R/S method were used to explore the influencing factors and predict the future trend. The results showed that from 2012 to 2019, the carrying capacity of water and soil resources in the whole Ningxia region shows an upward trend, but the overall situation is basically overloaded. The carrying capacity in Guyuan City is greatest in the Ningxia region. Based on the obstacle analysis, the driving force subsystem has the strongest restriction on the carrying capacity of water and soil resources in Ningxia. Economic density, natural population growth rate, per capita GDP, grain output per unit of arable land and per capita water resources are the main factors affecting the water and soil resources carrying capacity in Ningxia. According to the R/S method, in the future, the water and soil resources carrying capacity in Ningxia will show an upward trend. Guyuan and Zhongwei have a significant upward trend, while other cities have a weak upward trend.

In order to study the influence of climate change on rainfall extreme value distribution in main flood season, based on the daily rainfall data from 1960 to 2017 in Jiangxi Province, a variety of test methods were used to detect and test the abrupt change points. Genetic algorithm and Fisher's optimal segmentation method were used to stage the flood season before and after the climate abrupt change, and the extreme distribution of staged rainfall and design rainfall before and after the climate abrupt change were discussed. The results show that 1991 was the abrupt change year of precipitation in Jiangxi Province from 1960 to 2017, and it was necessary to pay more attention to the occurrence of extreme heavy rainfall in Guangchang and Poyang Lake regions. Genetic algorithm is suitable for the division and staging of flood season. After the abrupt climate change (1991-2017), the designed rainfall value in the main flood season of Jiangxi Province was greater than that before the abrupt climate change (1960-1990), and also greater than that in the whole period (1960-2017). When calculating the designed flood based on the designed rainfall, the influence of climate change on the designed rainfall value should be considered, and strengthen protection against floods.

Taking four small and medium-sized watersheds in the mountainous city (Chongqing) as the research objects, the application prospects of multi-source rainfall data in short-term hydrological forecasting were explored. The GPM-IMERG remote sensing precipitation data was introduced as the source of the satellite precipitation data, and the Mean Bias Correction (MBC) method, Linear Regression Model (LRM) and Geographically Weighted Regression (GWR) method were used to realize the fusion with the ground station measured data. A leave-one-out validation method was used to evaluate the accuracy of the fused precipitation data, and the SWAT model was applied to simulate the runoff of the selected basins using the precipitation data corrected by MBC, LRM, GWR, the original IMERG-early, and the measured data. The results show that the GWR was the best fused effect. The topography had great influence on the accuracy of the IMERG-early data and the fusion method. The accuracy of the fusion method was relatively high in low elevation regions, while in mountainous areas, the accuracy became low comparatively. The results showed a better agreement between the SWAT model and the measured runoff process using all kinds of precipitation data, in which the model using precipitation data corrected by GWR method was more accurate. Results can be referenced for hydrological forecast in similar small basins in the future.

Vegetation is an important part of terrestrial ecosystem and is vulnerable to extreme climate events. It is of great significance to explore the spatio-temporal evolution and dynamic response relationship between extreme climate events and vegetation for scientific response to climate anomalies and prevention of natural disasters. Therefore, the RClimDex, trend analysis and detrended fluctuation analysis were used to analyze the spatio-temporal evolution of extreme climate and NDVI in the Huaihe River Basin from 1998 to 2019, and discuss their causes and future variation tendency as well as clarify the response of NDVI to extreme climate. The results demonstrate that the NDVI shows an increasing tendency with an increase of 0.002 5 a^-1 from 1998 to 2019. Among the extreme climate indices, warm temperature indices showed an increasing tendency, while the cold temperature indices and precipitation indices (except RX1day) showed a decreasing tendency. The distribution of NDVI in the Huaihe River Basin was closely related to the distribution of urbanization in the region. The NDVI has a lag response of about one month to extreme climate and will continue to rise. The annual variation of the NDVI is closely related to natural and human factors, and the intra-annual variation of the NDVI is mainly affected by the growth rhythm of crops in the cultivated land.