甘肃黄土高原半湿润区4～10月降水气候特征分析

Analysis on the Climatic Characteristics of the Precipitation Between April and October in Semi-humid Area of Gansu Loess Plateau

用EOF和REOF等方法，对甘肃黄土高原半湿润区全部26个站1971年～2000年4～10月农作活跃生长季降水进行分解，分析其空间分布特征和时间变化规律．结果表明，甘肃黄土高原半湿润区4～10月降水量，具有明显的空间差异，最少的是西北部永靖站为428．9mm，最多的是东端正宁站为549．8m，4～10月降水在由南向北依次递减的总体趋势下，以天水为界，其东西两侧的变化呈“八”字形相反趋势：陇东地区，从东南向西北依次递减；临夏州和临洮、渭源一线，总体上由西南向东北依次递减．EOF及REOF分解的结果更为复杂．其时间演变规律是：26站多年多站4～10月降水综合平均值，年际间变化振幅十分明显，最大值出现在1984年为638．5mm，最小值出现在1982年为346．7mm，最大值是最小值的1．8倍多．20世纪70年代前期和90年代中后期为少雨时段，其余为相对多雨时段，90年代末以来，降水又有增加的趋势．就各年代各区域而言，70年代以庆城、宁县、华亭、清水一线为界，其以南以东低于多年平均，而以北以西高于多年平均；其中西部的东乡、广河也低于多年平均．而80年代研究区域整体均高于多年平均．90年代，整个区域均为负距平，尤其是其南部降水减少的更为明显．

Using EOF and REOF methods, the precipitation data of 26 meteorological stations between April and October from 1971 to 2000 in semi-humid area of Gansu Loess plateau were decomposed and the distribution characteristics and time trends were analysed in this paper. The results showed that the precipitation between April and October has a significant spatial difference with more precipitation in the eastern part and less in the northwestern part. The biggest value, 549. 8 mm, appeared at Zhengning and the least value, 428.9 mm, at Yongjing. The precipitation is getting less and less from south to north. To the east of Tianshui the precipitation is getting less and less from southeast to northwest, and to the west it is getting less and less from southwest to northeast. The time trend of the precipitation is that the annual change is very significant, and the biggest value, 638.5 mm, appeared in 1984 and the least value, 346. 7 mm, appeared in 1982. The precipitation is less during early 1970s and during mid-and-late 1990s. The precipitation is getting more and more since late 1990s. Druing 1970s, to the southeast of the line of Qingcheng, Ningxian, Huating and Qingshui the precipitation is less than the mean value, and to the northwest of the line it is more than the mean value. The precipitation is more than the mean value in the total study area druing 1980s. The precipitation is less than the mean value in the total study area during 1990s, significant especially in the southern part.