On the Characteristics of Response of Precipitation and Runoff to the ENSO Events in the Source Regions of the Yellow River
WANG Gen xu 1, 2 , SHEN Yong ping 1 ,LIU Shi yin 1 (1. Cold and Arid Regions Environmental and Engineering Research Institute, CAS, Lanzhou Gansu 730000, China; 2. Resources and Environmental College of Lanzhou University, Lanzhou Gan
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.