Spatial and Temporal Variations of Extreme Precipitation Events in the Red River Basin during 1960-2007

The temporal and spatial variations of extreme precipitation were studied by using extreme precipitation indices Based on the daily precipitation data of 23 meteorological stations over the Red River Basin in China from 1960 to 2007.The intensity and frequency of extreme precipitation gradually reduces from southeast to northwest,high value area was distributed along the south of the Jiangcheng-Luchun-Jinping-Hekou while low value area existed along the north of Weishan-Nanjian-Midu and the middle reaches of the Yuanjiang River Valley.The peak of extremely heavy precipitation occurred in July,while extreme precipitation occurrence frequency in flood season accounted for 91.48% of the annual total.In the past 48 years,an increasing trend was observed in indices such as the total wet day precipitation(PRCPTOT),the maximum 1-day precipitation amount(Rx1d),the maximum 5-day precipitation amount(Rx5d),the number of heavy precipitation days(R95N),the percent of total precipitation from heavy precipitation(R95T) and the simple daily intensity index(SDII),among which R95T and SDII increased significantly at the rates of 0.68%·(10 a)-1 and 0.17 mm·d-1·(10 a)-1 respectively.The trends of these indices exhibited spatial differences except for SDII,regions with the increasing trends are distributed mostly in the upstreams of the Lixianjiang and Yuanjiang rivers,as well as Tengtiao River Basin,while those of the decreasing trends were found in the downstreams of the Lixianjiang and Yuanjiang rivers,and Panlong River Basin as well.