Spatio-temporal variations of dry season rainfall and circulation analysis of typical drought years in the Xijiang River Basin

The rainfall data from 1961 to 2023 in the Xijiang River Basin and ERA5 (the fifth generation global climate and weather reanalysis product of the European Centre for Medium Range Weather Forecasts) data are used to analyze the spatio-temporal variations of dry season rainfall in the basin and the composite anomalies of 850 hPa wind and 500 hPa geopotential height during typical drought years are examined. The results show significant decadal variations in dry season rainfall in the Xijiang River Basin. Typical severe drought years may follow years which have positive anomalies of dry season rainfall, highlighting the need to consider rainfall of previous dry season when forecasting the next dry season rainfall in the basin with the attention of sudden turn of floods and droughts. In typical drought years, the duration without rainfall in the dry season in the Xijiang River Basin may generally be longer, but the duration without continuous rainfall days may not be longer. Dry season rainfall in the Xijiang River Basin shows an overall "less in the west, more in the east" distribution, with decreasing rainfall trends in the northwest and increasing trends in the northeast of the basin. Factors such as a strong European trough, weak polar vortex, strong high-pressure ridge near Lake Balkhash, strong East Asian trough, anomalous north wind over South China, and active and intense cold air may make the Xijiang River Basin to be widespread droughts.