Diurnal variations of summer precipitation in Beijing

Climatic characteristics and secular trends of diurnal variations of summer precipitation in Beijing are studied using hourly self-recording rain-gauge data during 1961-2004. The results show that both rainfall amount and rainfall frequency present high values from late afternoon to early morning and reach the minima around noon. Two separate peaks can be identified in the high value period, one in the late afternoon and the other in the early morning. Taking the rainfall duration into account, it is found that the rainfall during late afternoon to midnight mainly comes from the short-duration rainfall events (an event of 1-6 hours in duration), while the rainfall during midnight to early morning is accumulated mostly by the long-duration rainfall events (an event that lasts longer than 6 hours). In the recent 40 years, the summer precipitation in Beijing has been considerably restructured. The total rainfall amount of short-duration events has increased significantly, while the total rainfall amount of long-duration events has decreased.