基于前期降水指数的气象干旱指标及其应用

摘要

从气象干旱定义出发,考虑干旱累积效应,借鉴前期降水指数(API)和标准化降水指数(SPI),建立基于标准化前期降水指数(SAPI)的逐日气象干旱指标,并利用1961-2010年全国632个台站的气象资料分析SAPI的适用性特征.结果表明:逐日SAPI曲线呈典型“锯齿型”特征,在降水持续偏少时段平稳下降,克服了基于“等权累加”建立的综合气象干旱指数由于前期降水移出计算窗口而导致的“不合理旱情加剧”问题,能够精细刻画干旱发生、发展和结束过程.SAPI敏感性分析表明,加剧一个干旱等级需要的无雨日数在降水越少的季节(地区)越多,减缓一个干旱等级需要的日降水量在降水越少的季节(地区)越少.各等级旱日频率总体上与理论频率一致.降水量较少的季节(地区),轻旱、中旱及总旱频率略高于降水量较多的季节(地区),而重旱、特旱频率时空特征相反.1961-2010年全国平均各等级旱日频率均呈下降趋势,其中特旱较为明显,但具有复杂的时空特征:9-11月各等级旱日频率显著增加,其余月份以减少为主；各等级旱日频率总体上呈“西减东增”趋势.%According to the definition of meteorological drought, considering cumulative effect of drought, a daily meteorological drought indicator is presented based on the standardized antecedent precipitation index (SAP1), and the applicability of SAPI were examined by using daily precipitation data of 632 meteorological stations in China froml961 to 2010. SAPI shows a typical "jagged fluctuation pattern" and decreases steadily during rainless periods, thereby overcoming the "unreasonable drought aggravation" problem of the comprehensive meteorological drought index based on equal weight accumulation due to the antecedent precipitation moving out of the calculation window. SAPI is able to describe the processes of occurrence, development and end of drought accurately. Sensitivity analysis show that the needed rainless days to increase one drought level are more in areas or seasons with less rainfall than in those with more rainfall, and the needed daily rainfall to reduce one drought level is less in areas or seasons with less rainfall than in those with more rainfall. In general, drought days of various levels are consistent with their theoretical frequencies. Light and moderate drought days are slightly more in areas or seasons with more rainfall than in those with less rainfall, and the opposite is true for severe and extreme drought days. During 1961-2010, national-averaged drought days of each level all show decreasing trends, among which the trends in extreme drought days are most obvious but with complex spatial-temporal characters. Drought days of each level increase significantly in September-November, however decrease in most of the rest months. Drought days of each level overall decrease in the west but increase in the east of China.