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用历史降水和温度资料得到全球陆地区域(分辨率为2.5°×2.5°)1870~2002年间的月Pal-m ar干旱指数(PDSI)。伊利诺斯州、蒙古及中国与前苏联部分地区有土壤湿度资料,暖季的PDSI与实测土壤湿度(土层厚度为1 m)呈显著相关(r=0.5~0.7),夏末和秋季相关最好,而春季由于融雪的影响相关最差。对世界最长河流(其中7条)及几条其他河流进行分析,各流域平均的年PDSI变化与径流相关很好(r=0.6~0.8),表明PDSI可以很好地表征地表土壤湿度状况与径流。对PDSI进行经验正交函数(EOF)分析,揭示了由降水、温度趋势及ENSO引起的年际内变率所产生的线性趋势。全球严重干旱区(PDSI<-3.0)面积自20世纪70年代以来增加了1倍多,其中80年代初由于ENSO引起的降水减少造成干旱区面积的突增,后来的增加主要归因于地表增温;全球非常湿润区(PDSI>+3.0)面积80年代减少不明显。自1972年以来,全球极干或极湿地区面积从20%增加到了38%,80年代中期以后地表增温是其主要原因。这些结果为日益增加的干旱风险提供了观测证据,干旱风险的增加是人类活动导致全球变暖的结果。
The monthly Pal-m ar drought index (PDSI) over the global land area (resolution 2.5 ° × 2.5 °) from 1870 to 2002 was obtained using historical precipitation and temperature data. Soil moisture data were obtained in the states of Illinois, Mongolia, China and parts of the former Soviet Union. The PDSI in warm season was significantly correlated with the measured soil moisture (soil thickness 1 m) (r = 0.5-0.7) and summer and autumn The best, while the spring due to the impact of snow melting the worst. Analysis of the longest river (7 of them) and several other rivers in the world showed that the average annual change of annual PDSI in each basin was very good (r = 0.6-0.8), indicating that PDSI can well characterize the relationship between surface soil moisture and run-off. An Empirical Orthogonal Function (EOF) analysis of the PDSI reveals the linear trend resulting from precipitation, temperature trends and ENSO-induced interannual variability. The area of the global arid zone (PDSI <-3.0) has more than doubled since the 1970s, with a sudden increase in the area of arid zones resulting from a decrease in precipitation due to ENSO in the early 1980s, with the subsequent increase mainly attributable to the increase in the surface area Temperature; the area of the world’s very wet zone (PDSI> +3.0) was not significantly reduced in the 1980s. Since 1972, the area of extremely or very wet areas in the world has increased from 20% to 38% and the surface warming has been the main reason since the mid-1980s. These results provide observational evidence of the growing risk of droughts as a result of the increased risk of droughts as a result of human activities leading to global warming.