Based on the precipitation data of the 14 observing stations in Chaohu basin from 1961 to 2000,the spatial-temporal characteristics of precipitation in flood season are analyzed with the method of Z index and GIS.The results show that flood and drought disasters in Chaohu basin are frequent.There exists a positive correlation between the frequency of flood and drought and the precipitation.Flood and drought are periodicity.Their spatial distribution indicates a certain structure.The northern part of Chaohu ...