The Study On Some Problems Of Climate Change Of Drought And Flood In Global Land During 1948-2001

Based on the global land monthly rain data (PREC/L) created by Chen et al (2001), this paper investigates some problems of the climate change of drought and flood of global land during 1948-2001. The main contents and results are as follows.We first calculated the mean duration of drought and flood events, we found that the mean duration of drought and flood events has little spatial variability over the globe. The mean of the duration is about 1-1. 5 months, with a standard deviation of 0. 5 months. The mean duration of drought and flood events also has little secular trend.We then examined the mean separation time between two adjacent events. We found that the mean time interval between two adjacent flood, drought, severe flood, severe drought months has large spatial variability, from several months to more than one hundred months , over the globe. Globally , from the period 1948-1976 to the period 1977-2001 the mean severe flood to severe flood interval increased by 2. 4 months , or 7%, and the mean severe drought to severe drought increased 3.3 months(12%). cThe time series of drought and flood area from 1948 to 2001 in global land and in six large-scale region was analyzed. The result shows that the flood area has a marked decreasing trend in global land in summer and autumn and winter, while the flood area has a remarkable increasing in North America in spring. And the trend of drought area is markedly increasing in global land in spring and autumn, while the trendof drought area is remarkably decreasing in South America in autumn Theflood and drought area also has decadal variety in global.The relationship between flood area (drought area) and ENSO events was analyzed. Result shows the variation of flood and area is associated with ENSO events. The drought area is markedly increasing and the flood area is remarkably decreasing in global land in summer and autumn and winter in warm event, while the flood area in spring and autumn is markedly increasing and the drought area in spring is remarkably decreasing in Africa in warm event.The flood area increase markedly and the drought area is decrease remarkably in global land in summer and autumn and winter in cold event, while the flood area in spring autumn decrease remarkably in North America in cold event.