Climatic Characteristics and Trends of Precipitation for Different Grades in Jianghuai Region in Recent 45 Years

Based on meteorological observation data from 1979 to 2023 in the Jianghuai region and ERA-5 reanalysis data, this study analyzes the spatiotemporal variations of different precipitation grades and their influencing factors. The results reveal that total precipitation and precipitation below the heavy rain level exhibit a latitudinal distribution, decreasing from south to north, whereas extreme heavy rain is concentrated in the Dabie Mountains and the mountainous areas at the junction of Jiangxi, Anhui, and Zhejiang provinces. Precipitation shows a significant negative correlation with latitude and a positive correlation with altitude, with the correlation coefficient between extreme heavy rain and altitude reaching approximately 0.30. Over the recent 45 years, the total number of rainy days and light rain days has significantly decreased, while total precipitation and precipitation above the heavy rain level have significantly increased. This indicates that the overall growth in precipitation is driven by heavy precipitation events. Seasonal variability in precipitation becomes increasingly pronounced with increasing intensity: heavy rain and above occur most frequently in summer, while light rain is relatively evenly distributed across all seasons. The precipitable water has a good discrimination for different grades of precipitation in different seasons. Interannual variation of precipitable water is highly consistent with precipitation trends, particularly the number of days mean daily with precipitable water ≥60 mm and extreme heavy rain, suggesting that extreme moisture conditions are a key driver of heavy precipitation. Furthermore, years with above-normal extreme heavy rain are associated with a westward shift and stronger intensity of the western Pacific subtropical high, accompanied by anomalous wind patterns favorable to upward motion and moisture transport over the Jianghuai region. In contrast, during years with below-normal extreme heavy rain, the opposite pattern prevails.