Long-term precipitation change by hourly data in Haihe River Basin during 1961–2004

Hourly summer precipitation data recorded at 21 stations during 1961-2004 in the Haihe River Basin in North China were analyzed. The results show that the precipitation frequency and amount and the morning peak mainly relating to long-duration rainfall events decreased during this period, whereas the normalized afternoon peak mainly relating to short-duration events increased, which may suggest that the proportion of short-duration rainfall has increased as the total summer rainfall has decreased. For short-duration events, the mean intensity and peak intensity increased at most stations and the time to peak intensity decreased, which may be attributable to the higher thermal contrast between the warmer lower surface and cooler upper level. In the case of long-duration events, the total amount was significantly correlated with the East Asian summer monsoon index for the period 1961-2001 (correlation coefficient of 0.63). Although the total amount of rainfall in long-duration events decreased in the basin, the mean intensity and peak intensity, as well as the extreme hourly precipitation, increased in the western basin and decreased in the eastern basin.