标准化降水蒸散指数在中国干旱监测的适用性分析

Applicability Analysis of Standardized Precipitation Evapotranspiration Index in Drought Monitoring in China

针对国际上最新提出的干旱指数——标准化降水蒸散指数(SPEI),从拟合优度检验、对历史干旱事件的刻画、以及SPEI与SPI、PDSI指数的关系角度出发,全面分析了SPEI指数在中国区域的适用性。结果表明,只有在冬季且时间尺度小于3个月时,新疆南部、西藏西北部和华北至河套地区的样本不服从Log-logistic分布;而在冬季且时间尺度大于3个月以及夏季的任何时间尺度,中国范围的样本都符合Log- logistic分布,所得SPEI指数可靠。SPEI指数能够准确刻画几次特大干旱事件的地域中心、影响范围和强度。与SPI指数相比,SPEI指数引入了影响干旱的潜在蒸发项,能够更精确地刻画干旱。而与PDSI指数相比,SPEI指数具有多时间尺度特征,计算更简便。

The applicability of Standardized Precipitation Evapotranspiration Index(SPEI) in China has been analyzed.The main aspects of this research comprise goodness of fit test,capability in reproducing history drought events and the comparison between SPEI and Standardized Precipitation Index(SPI) and Palmer Drought Severity Index(PDSI),both of which are widely used in drought monitoring and analysis.The result of goodness of fit test shows that for the boreal winter and shortest time scales,the precipitation minus potential evapotranspiration series fail to match the presumed Log-logistic distribution in the south of Xinjiang,the northwest of Tibet and the area from North China to Hetao indicating the unreliability of SPEI values.With mentioned exceptions above,for most regions nationwide a good fit between the sample series and the Log-logistic distribution independent of the time scale and the month of the year guarantees the robustness of SPEI computation.Secondly,the comparison between spatial distribution of SPEI and China Historical Drought Dataset in typical years indicates that SPEI has good performance in measuring drought as well as flood.Furthermore,the relationship among SPEI,SPI and PDSI is also analyzed.The correlation coefficient between SPEI and SPI is roughly above0.8 for different time scales.However,how well the SPEI correlated with PDSI relies on the time scale.When the time scale is less than 10 months,the poor correlation is observed between SPEI and PDSI;when the time scale is greater than 10 months,the correlation coefficient between SPEI and PDSI remains between 0.7 and0.9.The comparison result shows that if the suitable time scale is chosen,the statistically based drought index,SPEI,has the similar capacity with PDSI which is based on complex soil water balance to describe and monitor drought reasonably.Furthermore,the SPEI has flexibility to adapt to intrinsic multi-scale nature of drought and advantage over simple calculation.