关键词: 干旱, 受旱面积, 受旱成灾面积, 中国

Abstract: Drought is normally defined as water shortage caused by the imbalance between water supply and demand.The fomation and intensity of drought are gradual cumulative processes.A new drought index considered the effect of rain shortage of early days is given in this paper.Three grades of drought:moderate,severe and extreme drought are divided.On the basis of the data of drought during 1951-1991,we analyse the area distribution of drought, including frequently-occurring drought.serious drought and continued drought. Based on the number of drought occurrences and an analysis of the average number of drought months,regional differences in drought oc currence are notable.The result shows that there are four large drought centers in China.It is shown from the time series of drought index that there is a linear tendency of drying in the whole country and in most areas.They are the Huang-Huai-Hai Plain region.the south China and Middle and Lower Yangtze River Region,the Southwest China Region and the Western Part of Northeast China Region. Using the time series the drought-affected area and the drought-damaged area in whole country,the impacts of droughts are discussed at last.The periodicity of drought-affected and drought-damaged areas in China has been significant in the last 40 years. During this time,three wet Periods and three dry periods occurred.The periods of 1958-1962,1971-1981,and 1986-1988 were observed as significant drought periods(i.e.,more than 20 million ha were affected).During the Periods 1950-1957,1963-1970,and 1981-1985,less than 20 million ha were affected.In total,seven severe drought years(1959,1960,1961,1972.1978,1986 and 1988) were recorded during the significant drought periods.In each instance,the drought-affected areas encompassed more than 30 million ha.The variability in the occurrence of drought-affected and damaged areas seems to increase during the last 40 years.Averaged by decades,the drought-affected areas in China from the 1950s to 1980s are 12.6,21.7,26.1 and 24.1 million ha,respectively.This trend is consistent with the general trend of summer aridization in China.It is concluded that there are periods with large drought-affected area and large drought-damaged area,and there is also a linear increasing tendency with the fluctuation.

Key words: Drought, Drought-affected area.Drought-damaged area, China