Forecast Of Summer Extreme Precipitation Over The Middle And Lower Reaches Of The Yangtze River

Based on high-resolution observation of daily precipitation data and monthly atmospheric circulation data,a physical-based empirical model was established to predict extreme summer precipitation in the middle and lower reaches of the Yangtze River?27°N-32°N,108°E-122°E?.Three predictors with significant correlations,independent of each other,and significant physical impact were selected.The three predictors are:spring sea surface temperature?NIO-SST?in the North Indian Ocean?20°S-20°N,40°E-110°E?,and Pacific Northwest?31°S-30°N,122°?.E-1480W)Spring sea surface pressure minus the Aleutian Seas?50°N-67°N,160°E-160°W?Spring Sea Surface Pressure?WNP-AI-SLP?,May Arctic Oscillation Index?M-AO?.The analysis of the physical mechanism shows that when the spring NIO-SST is high,the South Asia high voltage extends eastward and the western Pacific subtropical high voltage extends westward.The resulting secondary circulation causes abnormal upward movement of the middle and lower reaches of the Yangtze River.The water vapor transport in the basin increased,which led to an increase in extreme summer precipitation in the middle and lower reaches of the Yangtze River.When the WNP-AI-SLP was higher in spring,the surface pressure in the western Pacific Ocean was abnormally high,which was maintained by the cold-warm sea surface temperature in the sea area of the basin.At the same time,the heating from the North Indian Ocean to the middle and lower reaches of the Yangtze River also increases the extreme precipitation in the middle and lower reaches of the Yangtze River.When the M-AO is in a positive phase,the East Asian jet flows northward and the western Pacific subtropical high turns to the northeast.Shifting,causing the rain belt to move northward,the East Asian summer monsoon is enhanced,and there are obvious sinking movements in the middle and lower reaches of the Yangtze River,which are not conducive to precipitation.The regression model was established between 1961 and 1999 with a correlation coefficient of 0.61?p<0.01?.The independent prediction of the physical experience model during 2000-2014 showed a higher predictive power with a correlation coefficient of 0.52?p<0.05?.).Based on the weather forecast and research model?WRF?,the summer daily precipitation data?WRF₀25,resolution:0.25°*0.25°?of the middle and lower reaches of the Yangtze River in 2006-3030 under the RCP4.5 scenario were obtained.The observation data were used to verify the simulation ability of WRF₀25 test data for summer extreme precipitation in the middle and lower reaches of the Yangtze River in 2006-2014.Based on the analysis of WRF₀25 test data from 2015 to 2030,the temporal and spatial variation characteristics of extreme precipitation in the middle and lower reaches of the Yangtze River are discussed.The results show that the summer extreme precipitation in most of the middle and lower reaches of the Yangtze River shows a decreasing trend.Only the northwestern part of Hubei,Zhejiang and Fujian have an increasing trend;the extreme precipitation in the middle and lower reaches of the Yangtze River has obvious interannual.There are also obvious two-year cycles for changing characteristics.The physical mechanism of interdecadal variation and interannual variation of summer extreme precipitation in the middle and lower reaches of the Yangtze River under the RCP4.5 scenario is further analyzed.The results show that the decrease of summer extreme precipitation in the middle and lower reaches of the Yangtze River from 2015 to 2030 are related to the weakening of the summer monsoon and the obvious sinking movement in the middle and lower reaches of the Yangtze River;the increase of summer extreme precipitation and proportion in the middle and lower reaches of the Yangtze River in 2026 is related to the strong El Nifto phenomenon in the winter of 2025.