Regional summer precipitation events in Asia and their changes in the past decades

Abstract

A recently derived data set of daily precipitation is used to study the summer precipitation events over Asia and their changes in the decades of 1978–2002. Regional features of the precipitation over entire tropical‐subtropical Asia are investigated, exploiting the increased resolution and improved accuracy of the data set relative to other estimates. The changes in precipitation amount and precipitation days for total, extreme, heavy, and light‐moderate precipitations are examined. Although the Asian summer monsoon precipitation falls mostly in the form of light‐moderate rainfalls, regions of relatively frequent extreme precipitation events are found over South Asia and East‐Southeast Asia. These regions are separated by a narrow zone over the Indo‐China peninsula, along 100°E, where extreme precipitation rarely occurs. During the period examined, the amount of total precipitation and light‐moderate precipitation exhibits positive trends over southeastern and northwestern China, separated by negative trends over central China and southwestern and northeastern Asia. This sandwich‐like pattern, which also appears in the fields of precipitation days and soil moisture content, is associated with the enhanced water vapor supply related to the strengthened monsoon flow over southeastern China and the anomalous easterlies over northwestern China. It is also associated with the decreased water vapor supply linked to the weakened monsoon flows over southern‐southwestern Asia and central China and to the anomalous northerly flow over northeastern Asia. Over the entire tropical‐subtropical Asia, the largest changes in precipitation, atmospheric circulation, and water vapor transport occur over southern China. On the other hand, the changes over India are much smaller.