Declining frequency of summertime local-scale precipitation over eastern China from 1970 to 2010 and its potential link to aerosols

Summer precipitation plays critical roles in the energy balance and the availability of fresh water over eastern China. However, little is known regarding the trend in local-scale precipitation (LSP). 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 particular, more LSP events tended to form when the atmosphere was slightly polluted. Afterward, LSP was suppressed. These findings have important implications for improving our understanding of the climatology of daytime precipitation at local scales. Plain Language Summary Summer precipitation plays critical roles in the energy balance and the availability of fresh water over eastern China. However, the knowledge remains poorly understood regarding the trend of local-scale precipitation (LSP). Long-term hourly gauge data in the summer afternoon throughout eastern China for 1970 to 2010 reveal that LSP occurrence hours decrease at an annual rate of 0.25%, which differs greatly by region, ranging from 0.14% over the Yangtze River Delta to 0.56% over the Pearl River Delta. In contrast, large-scale precipitation events do not show significant increasing/decreasing trends over most regions. Further, concurrent visibility observations exhibit a decreasing trend, whose linkage to declining LSP is investigated. In particular, more LSP events tend to form as the atmosphere is slightly polluted. Afterward, LSP is suppressed. The findings provide deep insight into how precipitation changes over long term from a perspective of smaller spatial scale rainfall. Key Points A novel method developed to identify a local-scale precipitation event based on hourly rain gauge data A widespread declining trend of daytime local-scale precipitation events was observed in eastern China in summer for 1970 to 2010 Coincident increase in aerosol could partly account for the decreasing trend of local-scale precipitationNational Natural Science Foundation of China [91544217, 41405006]; Ministry of Science and Technology of China [2015DFA20870, 2013CB955804]; Natural Science Foundation of China [41471301]; Chinese Academy of Meteorological Sciences [2015Z003]SCI(E)ARTICLE115700-57084