Temporal and Spatial Distribution of Evapotranspiration and Its Influencing Factors on Qinghai-Tibet Plateau from 1982 to 2014

Evapotranspiration is the key driving factor of the earth’s water cycle, and an important component of surface water and energy balances. Therefore, it also reflects the geothermal regulation function of ecohydrological process. The Qinghai-Tibet Plateau is the birthplace of important rivers such as the Yangtze River and the Yellow River. The regional water balance is of great significance to regional ecological security. In this study, ARTS, a dualsource remote sensing evapotranspiration model developed on a global scale, is used to evaluate the actual evapotranspiration(ET) in the Qinghai-Tibet Plateau from 1982 to 2014, using meteorological data interpolated from observations, as well as FPAR and LAI data obtained by satellite remote sensing. The characteristics of seasonal. interannual and dynamic changes of evapotranspiration were analyzed. The rates at which meteorological factors contribute to evapotranspiration are calculated by sensitivity analysis and multiple linear regression analysis,and the dominant factors affecting the change of evapotranspiration in the Qinghai-Tibet Plateau are discussed.The results show that:(1) The estimated values can explain more than 80% of the seasonal variation of the observed values(R^2 = 0.80, P < 0.001), which indicates that the model has a high accuracy.(2) The evapotranspiration in the whole year, spring, summer and autumn show significant increasing trends in the past 30 years, but have significant regional differences. Whether in the whole year or in summer, the southern Tibetan Valley shows a significant decreasing trend(more than 20 mm per 10 years), while the Ali, Lhasa Valley and Haibei areas show increasing trends(more than 10 mm per 10 years).(3) Sensitivity analysis and multiple linear regression analysis show that the main factor driving the interannual change trend is climate warming, followed by the non-significant increase of precipitation. However, vegetation change also has a considerable impact, and together with climate factors, it can explain 56% of the interannual variation of evapotranspiration(multiple linear regression equation R^2= 0.56, P < 0.001). The mean annual evapotranspiration of low-cover grassland was 26.9% of high-cover grassland and 21.1% of medium-cover grassland, respectively. Considering significant warming and insignificant wetting in the Qinghai-Tibet Plateau, the increase of surface evapotranspiration will threaten the regional ecological security at the cost of glacial melting water. Effectively protecting the ecological security and maintaining the sustainable development of regional society are difficult and huge challenges.

Changes of Soil Erosion and Possible Impacts from Ecosystem Recovery in the Three-River Headwaters Region, Qinghai, China from 2000 to 2015

Soil erosion poses a great threat to the sustainability of the ecological environment and the harmonious development of human well-being.The revised universal soil loss equation(RUSLE)was used to quantify soil erosion in the Three-River Headwaters region(TRH),Qinghai,China from 2000 to 2015.The possible effects of an ecosystem restoration project on soil erosion were explored against the background of climatic changes in the study area.The model was validated with on-ground observations and showed a satisfactory performance,with a multiple correlation coefficient of 0.62 from the linear regression between the estimations and observations.The soil erosion modulus in 2010–2015 increased 6.2%,but decreased 1.2%compared with those in the periods of 2000–2005 and 2005–2010,respectively.Based on the method of overlay analysis,the interannual change of the estimated soil erosion was dominated by climate(about 64%),specifically by precipitation,rather than by vegetation coverage(about 34%).Despite some uncertainties in the model and data,this study quantified the relative contribution of ecological restoration under global climatic change;meanwhile the complexity,labor-intensiveness and long-range character of ecological restoration projects have to be recognized.On-ground observations over the long-term,further parameterization,and data inputs with higher quality are necessary and essential for decreasing the uncertainties in the estimations.

Analysis of Water Resources Carrying Capacity of the “Belt and Road” Initiative Countries based on Virtual Water Theory

Most countries along the route of the"Belt and Road"initiative are faced with a shortage of water resources.However,successful implementation of the initiative depends on water availability to support economic and social development.We designed a water resources carrying capacity evaluation index system,assigned grades and weights to each evaluation index and calculated a water resources carrying index for the 65 countries along the route.We used virtual water theory to analyze China's net virtual water import from key bulk agricultural products through international trade.For more than half of the countries along the route,their water resources will be unable to support the economic development that will be necessary for fulfilling the goals of the Initiative.As a country with insufficient water resources carrying capacity,China is a net virtual water importer in the virtual water trade.This virtual water trade can improve China's water resources support capacity,and ensure China's water and food security for the future.