Bureau of Hydrology Tibet

Potential evaporation is characterized by significant inhomogeneity over regions with high mountains and deep valleys. It is usually difficult to map sparse potential evaporation data over such regions for hydrological modeling and water resources management. This paper presented an analysis of potential evaporation estimation model for such a region, the Lhasa River basin in Tibet, China. The correlation of potential evaporation with the monitored meteorological factors including the water vapor pressure difference, air water temperature difference, air temperature, and wind speed, was analyzed. The applicability of the Dalton model corrected with air water temperature difference and believed to be universal for use in China was examined. An improved Dalton model that is corrected with both air water temperature difference and air temperature was then proposed. Residual error analysis proved its adequacy and verification against the monitored data showed its applicability. The improved model would be useful for mapping potential evaporation data over the Lhasa River basin.

Water loss and soil erosion is serious in regions with high mountains and deep valleys such as the Hengduan Mountains region in eastern Tibet.It is crucial to investigate the characteristics and predict the tendency of water loss and soil erosion in such regions.This study adopted the digital watershed model developed at Tsinghua University to model soil erosion in the Qamdo region,Tibet,as a case study.Scenario analysis was performed to explore the impacts of changes in precipitation,land use,and vegetation coverage due to climate change and human activities.It is shown that soil erosion will be significantly enhanced by increased precipitation;the decrease in precipitation or increase in vegetation coverage ratio will reduce soil erosion.Planting trees and growing grass could effectively control soil erosion,but the feasibility of 'conversion from farmland to forest and/or grassland' remains for future research.

Yamzho Lake, with a drainage area of 6, 100km2, is the largest closed interior lake in the southern part of the Qinghai-Xizang Plateau. The elevation of the lake stage is 4,440m, lake storage is about 16 billion m3. Water recharge mainly depends on rainfall, melting water from glacier area, taking up 16%. In the drainage basin about 2% of the area is covered with glacier. Seasonal range of variation in the lake stage is small, usually less than 0.6m. The biggest water level in a year appears in September or October, not in July or August of the rainfall concentrated period, because of the lake’s self-adjustment. The lowest lake level occurs in May, June or July. In wet years the stage fluctuation has clear periodicity, in dry years the lake level tends to fall down around the year. There is a close correlation between rainfall and water level variation. Based on the analysis of the patterns of the lake level fluctuation during the recent 100 years, according to the measuring and investigation data, the fluctuation range of the lake level varied at 4 to 5 meters, and the water level has been gently descending at the rate of 0.6m/100 years.