Contrasting Trend of Summertime Local-Scale Precipitation (LSP) and Non-LSP in Eastern China and Potential Link to Aerosol Pollution

Summer precipitation plays critical roles in the energy balance and has experienced significant changes due to the intense anthropogenic activities. However, our understanding with regard to the trend in local-scale precipitation (LSP) remains to be limited. Here we developed a novel method to determine LSP events in the summer afternoon throughout eastern China from 1970 to 2010 based on hourly gauge measurements. The LSP occurrence hours decrease at an annual rate of 0.25%, which varies considerably by region, ranging from 0.14% over the Yangtze River Delta to 0.56% over the Pearl River Delta. This declining frequency of LSP is generally accompanied by an increase in rain rate of LSP but a decrease in visibility, whose linkage to LSP events was investigated. In contrast, summertime non-LSP (NLSP) did not show any discernible changes, indicative of an observed contrasting trend for both LSP and NLSP. In particular, more LSP events tended to form when the atmosphere was slightly polluted. Afterward, additional aerosol particles tend to suppress LSP. These findings have important implications for improving our understanding of the climatology of daytime precipitation at local scales.