1986年以来黄河上游可利用降水量变化及对径流影响分析

Utilizable Precipitation Variations and Its Effects on Runoff in the Upper Reaches of the Yellow River Since 1986

以黄河上游兰州以上历年逐月可利用降水量为基本资料，分析确定1986年为近57年变化转折点，进而统计分析了1986年以来汛期可利用降水量较前期的时空变化，并依据天然径流量与其的关系，建立天然径流量计算公式，计算分析了可利用降水量变化和其它因素对径流量的影响。主要结论为：（1）可利用降水量年际变化特点有：①近57年总体呈减少趋势，并有前期偏多，中期基本正常和近期明显偏少的阶段性特点；②1986年前以正距平居多，之后则以负距平为主。（2）近期较前期变化特点有：①全年总量减少，主要由汛期总量明显减少所致；②尽管非汛期11、12、1、4月有所减少，但因2、3月显著增多使得其总量相对增多；③不同月份差异甚大，如5、10月变化不大，6月有所增加，7～9月明显减少；④夏秋季明显减少，冬春季有所增多；⑤中南部普遍减少20～60mm；⑥北部湟水流域变化不大；⑦西北小部分有所增加。（3）时段不同，可利用降水量变化和其它因素对径流的影响幅度不同：①20世纪80年代后期不及其它因素的影响显著（二者影响幅度比为2：8）；②20世纪90年代和近8年影响相对较为显著，二者影响的幅度比为3：7。

According to the basic data of monthly available precipitation quantity before Lanzhou station of Yellow River, the data collected in 1986 has been determined to be used as the turning point during the past 57 years. Based on the Calculating and analyzing the temporal and spatial variety of available precipitation quantity in flood season after 1986 comparing with that before the year, the calculation formula of natural runoff is set up according to the relationship between available precipitation quantity and natural runoff, which can be used to study the influence of available precipitation quantity variation and other factors on runoff. The main conclusions are.. （1） the characteristics of the annual available precipitation variations are. ①In the past 57 years, available precipitation quantity was decrease as a whole, and the available precipitation quantity was correspondingly high in prophase, normal in the middle and obviously low in recent years.②Before 1986, the majority was anomaly, whereas after that, the most part was negative anomaly. （2） The characteristic of available precipitation quantity change in recent years comparing with that in prophase are shown as below. ①The gross quantity decreased because rainfall decreased in flood season. ②Despite the precipitation decreased in non-flood season on November, December, January, and April, the total precipitation still relatively increased due to the significantly precipitation increasing in February and March. ③Substantial differences occurred in different months, such as little variations in May and October, a little increasing in June, significantly decreasing in June to September. ④The precipitation decreased obviously in summer and autumn, and increased in winter and spring. ⑤The precipitation decreased 20 to 60 mm universally in mid-southern part of China. ⑥The change was not obvious in Huangshui basin. ⑦Certain increase appeared in north-western part of China. （3） The influence of available precipitation variation was less obvious than that of other factors （ration of the former to the latter is 2 ： 8） in the latter part of 1980s and the influence was a bit notable in 1990s and recent 8 years （ration of the former to the latter is 3 ：7）.