中国西北地区伏期干旱指数及干旱分析

利用西北4省(区)137个气象站1971-2000年伏期(7～8月)总降水、蒸发资料,定义了干旱指数.分析了西北地区降水和蒸发的空间分布特征,以及定义的干旱指数确定的干旱分布状况,选取6个代表站典型湿润年份和特别干旱年份的干旱指数与Palmer指数的干湿等级进行比较.结果表明:伏期总降水量由西北向东南逐渐增加,最多是最少的66倍,蒸发量最大仅是最小的2～3倍,整个西北地区降水的变率比蒸发的变率大,定义的干旱指数反映了新疆南部、青海大部、甘肃河西走廊中部和甘南伏期干旱严重,干旱频率超过了80%,中旱出现最多,30年中各地适宜和湿润的年份不足1/3.6个代表站典型湿润和干旱年份的干旱指数与降水距平对应较好,湿润年份降水明显偏多,干旱年份降水明显偏少,与Palmer指数的干湿等级对干旱的状况描述接近.其中,干旱指数在对以庆阳为代表的西北地区东部的干旱状况反映更好.

Analysis on the Drought Index and Drought Events in Northwest China in the Hottest Season

In this paper, the drought index is defined using the total precipitation and evaporation dala from 137 meteorological stations in 4 provinces and autonomous regions in northwest China in the hottest season during the period of 1971 - 2000. Moreover, the spatial distribution of precipitation, evaporation, and drought events defined by the drought index are analyzed, and the drought indexes at 6 representative meteorological stations in relatively rainy and drought years are compared with Palmer Drought Index. The results show that the total precipitation in the hottest season increases gradually from northwest to southeast of northwest China, and the maximum precipitation is 66 times of the minimum one, but the maximum evaporation is only 2-3 times of the minimum one. The variability of precipitation is higher than that of evaporation in northwest China. The defined drought indexes reveal that drought is serious in south Xinjiang, most of Qinghai Province, central Hexi Corridor and south Gansu Province in the hottest season, and the drought occurring frequency is higher than 80%, in which the occurring frequency of moderate drought is the highest, and the occurring frequency of moderate and rainy years is less than one third in recent 30 years. The drought indexes at the 6 representative meteorological stations in typical rainy and drought years accord well with the anomalies of precipitation, that is the precipitation is significantly high in relatively rainy years but significantly low in drought years. These are similar to the situations defined by Palmer Index, however, the drought index can .ideally reflect the drought condi- tions in the Qingyang region located in the eastern part of northwest China.