1961-2013年黄土高原地区旱涝特征及极端和持续性分析

Extreme and persistent analysis of drought-flood variation in the Loess Plateau during 1961-2013

基于1961-2013年黄土高原地区54个气象站点逐日降水和气温资料,采用降水和蒸发均一化旱涝指数,从多时间尺度对旱涝的演变特征及极端和持续性旱涝事件进行分析,结果表明:①近53年,黄土高原地区具有明显的变旱趋势。②年代变化上,20世纪60-80年代整体偏涝,90年代整体偏旱,21世纪初进入全面干旱期;季节变化上,春、夏、秋、冬四季均呈变旱趋势,且最显著的是春、夏、秋三季;年代际旱涝变化存在突变现象,突变时间发生在1992年。③空间变化上,在降水和温度双重因子的共同驱动下,年际旱涝指数表示的变旱区域涉及整个黄土高原,四季的旱涝变化具有一定区域差异,但以大范围的涝转旱为主;春季显著变旱决定着年际变旱的空间分布。④年代际极端洪涝总体为减少趋势,而极端干旱则为增加趋势;春、夏、秋三季极端旱涝发生频次较多且最多的是夏季,春、冬两季极端洪涝的发生频次多于极端干旱,而夏、秋两季极端干旱的发生频次多于极端洪涝;极端干旱与极端洪涝分别在1989年和1996年发生增多和减少突变;增温对极端干旱/极端洪涝的影响越来越突出,是促进和维持极端干旱、抑制和减少极端洪涝的重要因素。⑤持续性干旱事件有增多的趋势,但干旱强度却呈减弱趋势;持续性洪涝事件总体为减少趋势,但洪涝强度并没有明显的趋势;持续性干旱事件与洪涝事件多发区主要集中在黄土高原西北部和东南部。

Based on the daily precipitation and temperature data of 54 meteorological stations in the Loess Plateau during 1961- 2013, by using homogenized drought- flood index（DFI） of precipitation and latency evaporation,extreme and persistent characteristics of drought- flood are analyzed in multi- time scale. The results showed that：（1） The Loess Plateau saw a significant drought trend in recent 53 years.（2） On the interdecadal timescale, water- loggings were frequent in the 1960 s, 1970 s, 1980 s, while the 1990 s was drouthy, then total drought period occurred since the early 21 st century. On the inter-seasonal scales, drought trends were found in four seasons, among them spring, summer and autumn were remarkable; Moreover,the interdecadal variation presented a jump phenomenon in 1992.（3） In spatial variation,driven by both precipitation and temperature factors, the interannual DFI indicated that there was a consistent drought trend in the whole Loess Plateau. There existed a regional difference of seasonal drought and flood variation, but the drought trend covered the wide range. The spatial distribution of interannual drought was determined by drought areas in spring.（4） The interdecadal extreme flood frequency decreased, while extreme drought increased. The extreme drought- flood frequencies were higher in spring, summer and autumn, especially in summer.The frequency of extreme flood was higher than that of extreme drought in spring and winter,however, in summer and autumn, it occurred in the other way. An abrupt increase of extreme drought occurred in 1989 while the number of extreme flood events was reducing since 1996.The impacts of temperature increase on extreme drought and flood were becoming more and more prominent, which was the important factor promoting and sustaining extreme drought, as well as repressing and reducing extreme flood.（5） A growing trend of persistent drought events was going on, while the intensity was weakening. The persistent flood events showed a decreasing trend, while their intensity was not obvious. The northwest and southeast parts of the Loess Plateau were frequency-occurring areas of persistent drought and flood events.