Climatic Characteristics of Water Vapor Resources over the Jinsha River Reaches and Its Surroundings

The Yangtze River rises in the Tanggula Mountains and the Qinghai-Tibet Plateau in southwestern China.The reach from Yushu in Qinghai Province to Yibin in Sichuan Province is called the Jinsha River,lying on the eastern edge of the Plateau and influenced by a variety of monsoon,e.g.,tropic monsoon,subtropical monsoon,and Qinghai-Tibetan Plateau Monsoon.This leads to a complex and particular climate.In the meanwhile,this region plays a prominent role in determining water resources of China.Water vapor resources,as the ultimate source of supply for the surface water and groundwater,are the key component of water resources.Moreover,most major impacts of climate variability and climate change on water resources over some critical regions still remain uncertain.Based on monthly precipitation and runoff in the Jinsha River Reaches,and monthly reanalysis data provided by the European Center for Medium-Range Weather Forecasts(ECMWF),climate characteristics of the water vapor resources over the Jinsha River Reaches and its surroundings were comprehensively examined.Results indicated that the precipitable water of the Jinsha River reaches attains the minimum in winter and the maximum in summer,with an evident seasonal variation.The Jinsha River reaches lies on the maximum meridional grads of the precipitable water around the Plateau,significantly affected by the Plateau.In winter and spring,the moisture over this region comes mainly from the middle-latitude westerly water transports,among which,the south branch water vapor transports south to plateau are of particular importance.In summer,the moisture originates mainly from the Bay of Bengal,the South China Sea,and the west Pacific Ocean.In autumn,the water vapor is from the South China Sea and the West Pacific Ocean.Since the 1960s,through the main water vapor source and water vapor transport channels of the Jinsha River reaches,the atmospheric precipitable water had an increased trend in general,in particular showing an evident increasing trend since the 1990s.From 1958 to 2002,the water transport of most Jinsha River reaches were enhanced in summer largely caused by the enhanced zonal transport.Variations in precipitation and runoff,and frequent extreme weather and climate events over the Jinsha River reaches since the 1990s appeared to be closely related to changes in the water vapor resources.Soil erosion in the Jinsha River of Yunnan Province is significant.Much attention should therefore be paid to ecological construction in the context of increased heavy rainfall events in the future.