Possible causes of the significant decrease in the number of summer days with light rain in the east of southwestern China

Abstract

Abstract In this paper, we investigated the spatio-temporal characteristics of the amount of light rain and the number of days with light rain in the ESWC and explored the possible causes of the significant decrease in the number of days with light rain. The results show that: (1) Both the amount of light rain and the number of days with light rain over the ESWC in summer showed a decreasing trend, with linear trends of −1.5 mm/decade and −0.88 day/decade, respectively. The decrease in the number of days with light rain was more distinct than the decrease in the amount of light rain. (2) The decrease in the number of days with light rain was closely related to the decrease in the relative humidity caused by an increase in temperature and specific humidity. The trend in relative humidity resulting from an increase in temperature alone was −1.1%/decade, whereas the trend in relative humidity caused by an increase in specific humidity alone was 0.29%/decade. The trend in relative humidity was −0.76%/decade. The decrease in relative humidity was mainly a result of an increase in temperature. (3) The increase in temperature resulted in a decrease in the relative humidity and an increase in the surface evaporation. The increase in evaporation increased the specific humidity, which, in turn, increased the relative humidity. This compensated for the decrease in the relative humidity caused by the increase in the temperature and further decelerated the decrease in the number of days with light rain.