甘肃黄土高原干旱半干旱区4～10月降水的气候特征

对甘肃黄土高原干旱半干旱区12个站1971-2000年4～10月降水，用EOF和REOF方法进行了分解，分析其空间分布特征和时间变化规律．结果表明，甘肃黄土高原干旱半干旱区4～10月降水具有明显的空间差异，最少的是景泰站为175．2mm，最多的是广河站为449．4mm，并呈从北到南、从西到东依次递增的态势，景泰有一干舌，一直南压到兰州、永靖一带，广河有一湿舌，北抬到榆中附近，南部和北部具有相反的分布趋势．其年际间变化振幅十分明显，最大值出现在1978年为415．0mm，最小值出现在1982年为199．1mm，最大值是最小值的1倍多．20世纪70年代初、80年代末和90年代后期为少雨段，其余时期为相对多雨时段，特别是90年代以来，降水呈持续减少的趋势．70年代其西部和东部减少，其余增加，80年代西部减少，东部增加，90年代西北部增加，东南部减少，综合反映出甘肃黄土高原干旱半干旱区4～10月降水时空分布特征的复杂性．

The Climatic Characteristics of the Precipitation Between April and October of Arid & Semi-Arid Area in Gansu Losses Plateau

Using EOF and REOF methods,the precipitation data of 12 meteorological stations through April and October from 1971 to 2000 located in the arid & semi-arid area in Gansu Losses Plateau were decomposed,and the distribution characteristics and time trends were analysed.The results showed that the precipitation through April and October has significant spatial difference,the minimum value,175.2 mm,appeared in Jingtai and maximum value,449.4 mm,appeared in Guanghe.,and the precipitation is getting more and more from north to south and from west to east,there is a "dry tongue" in Jingtai,tent to Lanzhou,Yongjin,and there is a "moist tongue" in Guanghe,tend to near Yuzhong,and the distribution is opposite in the south and norh.The time trend of the precipitation is that annual change is very significant,and the maximum value,415.0 mm,appeared in 1978 and minimum value,1991.1 mm appeared in 1982, the maximum is more than and time compared with minimum.The precipitation was less duing early 1970s,end of 1980s and late 1990s,other time were more,especially since 1990s the precipitation has shown a significant decreasing trend.In the study areas,During 1970s in west and east the preciptation was less than the mean value other areas were more,during 1980s west was less and east was more,and 1990s northwestern more and southeastern less,showing the complexity that the climatic characteristics of the precipitation through April and October of arid & semi-arid area in Gansu Losses Plateau.