中国现代干旱灾害的时空特征

CHARACTERS OF TIME-SPACE OF RECENT DROUGHT IN CHINA

本文提出了一个考虑前期降水短缺影响的干旱指数。利用１９５１－１９９１年逐月全国１６０个站的降水资料划分干旱等级，分析了我国干旱，包括多旱、重旱和持续干旱的区域分布，指出我国主要有四大干旱中心；分析了干旱随时间的变化，发现全国及多数区域的现代干旱存在着线性增长的趋势。最后利用全国干旱受灾和成灾面积讨论了干旱的影响，指出全国近代干旱受灾和成灾面积存在着三个高值期，且总体线性增长趋势也很明显。

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.