Based on the ground radiation observation data of Hubei Huashi photovoltaic power station from April to September in 2022, the forecast accuracy of the ground radiation products of Wind Energy and Solar Energy Forecasting System of China Meteorological Administration (CMA-WSP) was evaluated. Overall, the correlation coefficient between ground solar radiation and observation in the next 5 days predicted by CMA-WSP is between 0.85 and 0.91, and the forecast effect on the first day is the best. With the increase of forecast time, the forecast accuracy gradually decreases. From the perspective of month-by-month effect, the CMA-WSP has the best effect on ground radiation forecasting in August and September, and the forecast accuracy rate in May and June is relatively low. In terms of daily changes, the CMAWSP has a relatively poor forecasting effect on ground radiation at 10:00~16:00, and is better in other periods. The prediction of ground radiation by CMA-WSP has strong seasonality. The forecast results of different times in spring are quite different, and are relatively stable in summer. The forecast effect in autumn is the most stable, and the correlation coefficient between the prediction results and observation can reach 0.92. In general, the CMA-WSP has a good effect on the ground radiation forecasting in Hubei Province, which can provide good support for the short-term forecasting of photovoltaic resources in Hubei Province.

Based on the daily precipitation data of 38 meteorological stations in the Huaihe River Basin from 1961 to 2020, the consecutive dry days (CDD) were selected. The variation characteristics of CDD and its response to 12 circulation index at different time scales were analyzed by using M-K trend test, principal component analysis, the lag correlation analysis and cross wavelet transform. The results indicate that the spatial distribution of CDD in Huaihe River Basin had obvious seasonal characteristics. It was high in the west and low in the east in summer, and high in the north and low in the south in spring, autumn and winter. In the past 60 years, the changes of CDD in different seasons were also different. The CDD increased in most stations and the basin tended to become dry in autumn, but the CDD decreased in all stations and drought slowed down in the basin in winter. The CDD with different time lags had good correlations with the WP, SOI and Nino4, and the strongest correlation with Nino4. The Nino4 had a significant strengthening effect on the CDD with a lag of 4 and 5 months, and a significant weakening effect on the CDD with a lag of 10 and 11 months. The significant influence of Nino4 on CDD was mainly concentrated in the resonance period of 10-15 months, and there was a significant negative correlation between Nino4 and CDD. The finding is prone to useful for drought prediction and water resources management in the future.

Analyzing the spatial and temporal characteristics of extreme precipitation and the response of wind speed before and after extreme precipitation are of great significance for extreme precipitation characterization, improving the understanding of the relationship between extreme precipitation and wind speed, as well as managing water-related disasters. This study defined event-based extreme precipitation by considering preceding and succeeding precipitation, and classified precipitation patterns into three types, i.e. early peak, later peak and bimodal types according to the locations of precipitation peak, after which the spatiotemporal distributions of extreme precipitation and its relationship with wind speed were analyzed. The results show that single-peak of extreme precipitation occurs more often than bimodal one, and the amount increases from northwest to southeast, with significant upward trend of extreme precipitation detected; Extreme daily precipitation threshold increases with higher wind speed over the southeast and northeast, contrary to the southwest; Moreover, wind speed tends to show anomalies before and after extreme daily precipitation, and it decreases when extreme daily precipitation occurs over the southwest; However, over other regions, it increases before extreme daily precipitation and decreases after then, reaching the peak at the extreme daily precipitation day.

In response to the complex mechanism of runoff yield and concentration, insufficient groundwater monitoring data, and low accuracy of runoff prediction in Karst areas, a similarity prediction method that integrates physical mechanisms and data-driven approaches has been proposed. The optimal combination prediction scheme has been established for different flow magnitudes, prediction factors, and preceding affected lag-time, which can achieve adaptive matching and intelligent switching of multiple modes under different water and rain conditions. It can generate interpretable runoff prediction results. This method is applied to the runoff prediction of Longtan Hydropower Station. The results indicate that this method improves the accuracy and effective prediction period of runoff in Karst areas, which has scientific significance and practical value for ensuring the scientific scheduling and safe operation of large power plants.

In order to quantitatively analyze the impact of upstream reservoirs and the operation of the Three Gorges Project on the hydrological rhythms of the lower reaches of the Yangtze River and lakes, M-K test, cumulative anomaly method, wavelet coherence spectrum method and other hydrological time series trend analysis methods with STL time series decomposition method were used to analyze the 49-year historical water level data of Sheshan Station at Lake Shijiu. The long-term change trend and law of hydrological rhythm of Lake Shijiu under the new relationship between Yangtze River and Lake Shuijiu were analyzed. The coherent relationship between hydrological rhythm changes and local meteorological factors were analyzed along with the ecological effects under the new river-lake relationship. Under the new river-lake relationship, the dry season is earlier and longer and the averaged water level is higher, the extreme low water level is more likely to occur, the variation is gentler, and it is difficult for high water level to happen. The extreme high water level in the flood season is lower and happens later, the averaged water level is lower, ends earlier, and the amplitude is gentler. The early dry season is beneficial to increase aquatic plant biomass, but the decrease of water level variation in dry season may cause biodiversity to decrease.

In order to study the water logging risk in lakeshore urban caused by the blocking drainage effect (BDE) of Poyang Lake, the "regulation and storage model" was used to elucidate the BDE of Poyang Lake on inner river drainage in Changnan District and to explore the impact of Poyang Lake on waterlogging risk of lakeshore urban. By defining the Index of Blocking Drainage (IBD) which quantifies the BDE, the main controlling factors that affect the IBD was explored and the response relationship between them was quantified. The results show that the main controlling factors affecting the IBD include rainfall intensity, water level of outer river, drainage capacity and storage space. There is an obvious quadric curve relationship between rainfall intensity and the IBD, and 11.67 mm/h is the inflection point of the curve. There is a four-quadrant risk diagram relationship between the IBD and the water level of outer river. The decrease frequency of the IBD increases with the increase of drainage capacity. The effect of reducing the IBD by improving the drainage capacity of Changnan District is obviously reduced when the rainfall intensity exceeds 11.67 mm/h. The IBD of the same rain intensity decreases gradually with the increase of storage space. The effect of reducing the IBD of Qingshanhu District by increasing the storage space is obviously reduced when the rainfall intensity exceeds 15.83 mm/h. The water logging risk in lakeshore urban caused by the DBE of Poyang Lake can be effectively reduced by appropriately improving the drainage capacity, reducing the proportion of impervious ground and increasing the adjustable storage space, but the ability to deal with extreme rainstorm events remains limited.

Aiming at the falling into locally optimal solution shortcomings of optimization algorithm and probability density method for inversion of river cross-sections in ungauged regions, this paper proposed a combination of Ensemble Kalman Filter (EnKF) method and particle swarm optimization algorithm (PSO). The PSO was used to initialize the missing section to form a trapezoidal initial section. Then the EnKF was used to correct the initial section, and the proposed method was verified by the ideal case. The results show that the R² and N_NSE of the model are higher than 0.99, and the relative mean square error is less than 0.04. Considering the observation errors in the engineering practice, the observation errors of 0.1%, 1%, 5% and 10% were selected to evaluate the hydrodynamic simulation errors of the missing section, the PSO initial section and the corrected section by the EnKF method. It is found that the errors are normally distributed with the selected errors, but the overall distribution is normal with different errors. But the EnKF method can maintain a high simulation accuracy with different observation errors, the R² is higher than 0.98, the relative mean square deviation (RMSD) is less than 0.06 m, and the N_NSE is higher than 0.98. Thus, the proposed method has a high feasibility.

To analyze the impact of the construction of the Hengsha Dongtan (Phase 6-8) project on the Yangtze River Estuary, a two-dimensional tidal flow model was established using Delft3D, and tidal level and velocity calibration verification was conducted using existing hydrological data from 2008 and 2016. Based on the hydrological conditions in normal and flood years, the hydrological conditions, such as tidal volume, tidal level, and flow field in the main tributaries of the Yangtze River Estuary before and after the implementation of the Hengsha Dongtan Phase 6-8 Project were simulated. The results show that under two flow conditions, the construction of the Hengsha Dongtan Phase 6-8 project has a relatively small impact on the rising and falling tide flows of the main tributaries of the Yangtze River Estuary. The variation of high and low tide levels in the Yangtze River Estuary does not exceed 0.01 m, and the variation of high and low tide levels in the water area where the project is located does not exceed 0.02 m; The project has no significant adverse impact on the large-scale flow field structure of the Yangtze River Estuary. The rising tide velocity of the Beigang Waterway and Beigang Beisha Jiahong has decreased, with a maximum decrease of 0.03 m/s in Beigang Waterway and 0.02 m/s in Beigang Beisha Jiahong. The rising tide velocity of the Hengsha Channel and the North Channel of the Yangtze River Estuary has remained basically unchanged. Under the current riverbed terrain and engineering boundary conditions (all of the Hengsha East Beach project has been completed), there is a northwest southeast channel on the northeast side of the beach surface. The northern edge of the eighth phase project and the northern edge of the downstream sand body have a high ebb tide velocity, with a maximum velocity of 1.5 m/s or above, which is not conducive to the stability of the Hengsha East Beach regulation project.

In order to reduce the impact of bridge pier groups on the water flow at the intersection of the main rivers of Hangzhou Zhijiang New City, three shoreline optimization schemes were studied to improve the flow pattern based on a two-dimensional mathematical model. The optimal remediation plan was recommended based on multiple objectives such as water resistance ratio, land area, water area, bridge pier safety, and so on. The results show that the widening one side of the river channel to prevent bridge piers from being located in the main channel or changing the route to avoid bridge piers can effectively reduce the impact of bridge piers on the water level. The three optimization schemes have the same improvement effect on the backwater of the bridge piers. Scheme 2 and scheme 3 will affect the safety of bridge piers, with relatively small water area and large land acquisition area. Scheme 1 has little impact on the safety of bridge piers and is relatively easy to implement. Scheme 1 has high comprehensive advantages, and is recommended as the optimal option.

The scour of seawall toe is the one of the main factors for influencing structural stability of seawall estuary. The study of the scour characteristics at seawall toe under complex hydrodynamics and prediction method is of great significance for the seawall stability. Based on the field monthly measured topographic data since 2010, the time evolution of toe scour at Xijiangtang Seawall in Qiantang Estuary was discussed and the influence of flood was identified. The research results show that the seawall toe is eroded during flood, while there is silting during tide, and the critical flood discharge for scouring is about 5 000 m³/s. Based on the theory of sediment carrying capacity and riverbed deformation, a new scour prediction method is developed and the relative error is significantly improved within 20%.