Spatiotemporal Evolution of Extreme Precipitation Events in Shaanxi Province during the Period 1961-2007

In this paper,the spatiotemporal change of annual extreme precipitation events is analyzed using the daily precipitation data observed by 78 meteorological stations in Shaanxi Province during the period 1961-2009. The results show that the threshold of extreme intensity precipitation varied in a range of 18.7-9.5 mm/d,and it decreased northward. The extreme precipitation events in the province occurred mainly in rainy season from May to September,especially during the period from July to September,their duration was mostly for one day,the extreme precipitation events with 2-day duration occurred mainly in the central-southern part of south Shaanxi Province,and those with 3-day duration were occasional. The change trend of annual extreme precipitation events in the province was not significant in recent 49 years,but the extreme precipitation events increased in summer. The EOF results reveal that there were 2 main spatial distribution patterns of frequency of extreme precipitation events in the province. The first one (EOF1) was that the high or low frequency of extreme precipitation events was accordant in whole province,and there were 22-year and quasi-8-year periodic changes. The second one (EOF2) was that the frequency of extreme precipitation events in the southeastern part was opposite to that in the northwestern part,and there were the 12-14-year and 2-3-year periodic changes.