黄河源区降水与径流过程对ENSO事件的响应特征

On the Characteristics of Response of Precipitation and Runoff to the ENSO Events in the Source Regions of the Yellow River

根据最新季分辨率ENSO指数序列所确认的近 40多年来所发生的 2 0次ENSO事件 ,并确定了每次ENSO事件强度及其影响年 ,通过对相应年份黄河源区降水与径流距平变化值的对比 ,分析了降水与径流过程对ENSO事件响应的统计规律 :ENSO事件与黄河源区降水与径流年际波动变化有很好的相关性 ,这种相关性与ENSO事件的性质强弱、发生季节以及持续时间等有关 ,一般夏秋季暖事件无论强弱均使影响年降水减少 ,发生于春季的中等强度暖事件使发生年降水呈负距平 ,影响年降水呈增加趋势 ;冷事件与暖事件对降水的影响正好相反 ;暖事件对应年份黄河源区径流量减少 ,而冷事件则使其增加 .随着 2 0世纪 90年代以来暖事件发生频率的增加 。

In the source regions of the Yellow River (above the Tangnag Section), runoff is mainly nourished by precipitation, accounting for 64 1% of the total. Owing to climate change, variation in precipitation would result in runoff change in the source regions. According to a new ENSO index, which has a seasonal resolving ability, 20 ENSO events are identified from the spring 1952 through the spring 1998. There are 13 warm phase events and 7 cold phase events recognized. The strength and influence duration of each ENSO event is confirmed. Comparing the precipitation and runoff changing processes with the relative ENSO events, a statistical responsive relationship of precipitation and runoff to ENSO events in the source regions of the Yellow River are worked out in this paper. It is found that the annual fluctuation of precipitation and runoff in the source regions are obviously interrelated to ENSO events. The interrelationship was associated to the features, strength, occurring season and duration of the event. Generally, a warm phase event occurring in the summer and autumn may decrease the precipitation in the influence duration no matter how the strength of the ENSO event is. A warm phase event with middle strength occurring in the spring season would decrease the precipitation in the occurring duration, but would increase the precipitation in the influence duration. On the contrary, the cold phase event may increase the precipitation in the source regions. A warm phase event would decrease the runoff in the source regions. On the contrary, a cold phase event can increase the runoff. Because the occurring rate of the warm phase event has increased since the 1990s, runoff has a decrease trend in the source regions of the Yellow River.