Search

In the context of global warming, the frequency and intensity of extreme climate events, especially extreme precipitation events, have increased. The middle and lower reaches of the Yangtze River Basin are important areas for economic development, and are also one of the areas where rainstorms and flood disasters frequently occur in China. Improving the prediction of future summer extreme precipitation in this region under the greenhouse gas emission pathway that aligns with sustainable economic development (Representative Concentration Pathway 4.5, RCP4.5) will help decision-makers better cope with the impact of increased natural disasters, such as floods. The medium-resolution CESM1.0 (Community Earth System Model 1.0) data (1° × 1°) has limitations in capturing regional climate differences. Therefore, we designed a downscale experiment using the WRF3.8 (Weather Research and Forecasting 3.8) model to obtain the daily summer precipitation grid data with 0.25° × 0.25° latitude and longitude resolution over the middle and lower reaches of the Yangtze River Basin from May to September in 2006–2030 (WRF025). The research shows that the WRF025 data is reliable in simulating the summer extreme precipitation events over the middle and lower reaches of the Yangtze River Basin, especially in the lower reaches of the Yangtze River. Compared to CESM1.0 data, WRF025 data significantly improves the ability to simulate the numerical value and distribution of summer extreme precipitation in the middle and lower reaches of the Yangtze River. Under the RCP4.5 scenario, compared to 2006–2014, there is no significant change in daily summer precipitation in the middle and lower reaches of the Yangtze River Basin during 2015–2030, with a significant decrease in daily summer extreme precipitation. There are significant regional differences in spatial distribution, with a significant decrease in Hunan and Hubei, and a significant increase in Jiangxi and Fujian. Under high-pressure control, the lower reaches of the Yangtze River are dominated by downdraft, resulting in more sunny days and less precipitation. The increase (decrease) in water vapor transport and divergence may be the reason for the increase (decrease) in extreme precipitation. The most direct factor leading to an increase (decrease) in extreme precipitation is the vertical movement upwards (downwards). Furthermore, the anomalous descent (ascent) can be well explained by the easterly (westerly) wind anomaly on the southern (northern) side of the anomalous anticyclone via the isentropic gliding mechanism.

Characteristics of extreme precipitation over Yellow River Loop Valley (YRLV) and links to European blocking are investigated in this study. Spatial and temporal analysis of extreme precipitation shows that it contributes more than 30% of the total summer precipitation in the YRLV and is characterized by a strong and short period of local rainfall. Most of the extreme rains in the YRLV occur in July and August. Two typical circulation patterns were identified using a k-means clustering method. The extreme precipitation results from the combined actions of intensified high pressure over northeast China (NECH) and the westward extension of the western Pacific subtropical high (WPSH). The intensified southerly flow of the amplified NECH strengthens the water vapor transport induced by the westward extension of the WPSH from the northwest Pacific or Bay of Bengal into the YRLV. The NECH is amplified by the wave energy propagating from European blocking via the Silk Road pattern (SRP). This is the subseasonal cause of extreme precipitation over the YRLV. The composited July and August mean 500 hPa geopotential anomaly pattern for extreme precipitation years shows a high-pressure anomaly over the European continent and a negative phase of the SRP. The former provides a background for the occurrence of European blocking, and the latter explains the preexistence of the NECH and provides a linkage between the activity of European blocking and the subseasonal evolution of the NECH. Thus, the interannual variation in the extreme precipitation over the YRLV is mainly reflected by the phase of the SRP and the stationary waves over Europe.