Spatial and diurnal characteristics of summer rainfall over Beijing Municipality based on a high-density AWS dataset

On basis of quality-control of hourly rainfall dataset of Automatic Weather Stations (AWSs) for the last 4years (2007-2010), the spatial and diurnal characteristics of summer rainfall in Beijing Municipality (BJM) is analyzed. Results show that the short-duration heavy rainfall events dominate summer rainfall in the study area. Rainfall events with 1-3h duration make a large contribution to both frequency and amount of summer rainfall, and the total rainfall amount in summer fall almost in the events with duration less than 6h. Two peaks in diurnal variation of rainfall event frequency are evident, with one in early morning and another in later evening, but only one peak in later evening occurs for diurnal variation of rainfall amount. The exact timing and magnitudes of the peaks vary from one station to another probably due to the influence of the complicated terrains and geographical conditions. Except for the southeast area of the BJM, however, the highest frequency of rainfall events always occurs in evening between 1900 and 2300 (Local Standard Time, or LST), almost consistent to the occurrence time of the maximum rainfall amount. The peak of rainfall event frequency over the southeast area is generally in early morning (0300-0500 LST) which might have been related to the combined influences from land-sea breeze and urbanization.