1956-2012年黄河源区流量演变的新特征及其成因

利用黄河源区唐乃亥水文站1956-2012年的逐月流量实测资料，通过趋势分析、小波分析以及不均匀系数和贡献的计算，分析了1956-2012年57 a来黄河源区流量的趋势、年内双峰型变化新特征及其主要成因.结果表明：近57 a来黄河源区流量演变包括2个上升时段（1956-1967年和2002-2012年）、1个下降时段（1989-2002年）和1个振荡调整时段（1967-1989年）.流量年内分配不均匀性最大的是1980年代，最小的是1990年代.流量年内分配主要表现为双峰型，峰值点主要出现在7月和9月，但出现月份存在年际、年代际变化，且峰值点的月份也随着丰、枯水年存在着变化.降水对流量的正贡献呈7、9月双峰型，温度的负贡献则使9月峰值消失.当夏季高原附近区域，尤其是高原北侧低层600 hPa位势高度场降低，高原夏季风偏强时，有利于黄河源区降水增加、流量增大，出现流量年内分配的峰值点，且夏季高原高度场的变化对流量年内分配第二个峰值点（秋季）的出现有一定的指示意义.

Characteristics and reasons of the runoff variation in source regions of the Yellow River during 1956-2012

Based on the monthly runoff data in Tangnag during the period of 1956-2012, through trend analysis, wavelet analysis and calculation of inhomogeneity coefficient and contribution, the characteristics of runoff variation in the source regions of the Yellow River are analyzed. It is found that during the 57 years, there were two runoff rising stages (1956-1967 and 2002-2012), one runoff falling stage (1989-2002) and one runoff oscillation-adjusting stage (1967-1989); the annual runoff distribution in the 1980s was the most uneven, while that in the 1990s was the evenest; an average monthly runoff's characteristic was bimodal, with peaks appearing in July and September; the appearance of the peaks had annual and decadal variations. The wet years gave priority to bimodal distribution, the normal years gave priority to unimodal distribution. However, in dry years, the type of the annual runoff distribution was uncertain. The annual runoff distribution depends on the contribution difference between rain and temperature: the rain resulting in positive contribution and in bimodal distribution in July and September, but temperature resulting in negative contribution, which caused the peak in September disappearing. While in summer, the geopotential height field nearby the Tibetan Plateau reduced, especially in the north regions. The plateau summer monsoon strengthening makes wind field anomaly convergence in lower-level, makes moisture in the source regions of the Yellow River convergence and updraft, resulting in rise in precipitation in the regions, finally, increasing runoff and then first peak appearing. What is more, the change in the summer geopotential height field implies that the second peak of the annual runoff contribution will appear.