Hydro-climatic changes and their impacts on vegetation in Xinjiang, Central Asia

Central Asia is one of the most arid regions in the world. Xinjiang is the core area of the arid region in Central Asia. Climate warming and hydrological changes might affect the vegetation dynamics in the region; however there has been no systematic evaluation of the hydro-climatic changes and their impacts on vegetation in Xinjiang. In this study, the vegetation growth and its response to hydro-climatic changes from 2003 to 2013 were analyzed based on multiple satellite observations. It was found that precipitation increased, with fluctuations, at a rate of 12.07 mm/decade, and evapotranspiration decreased, also with fluctuations, at a rate of -14.79 mm/decade. The change in total water storage, derived from the Gravity Recovery and Climate Experiment satellite, displayed an increasing trend, with a rate of increase of 112.91 mm/decade. The changes in the Global Land Data Assimilation System-derived soil moisture and groundwater estimated by the water budget presented a slight increasing trend from 2003 to 2013. The total water storage, soil moisture, and groundwater all significantly increased after 2008, and the increases in soil moisture and groundwater had positive effects on the increasing total water storage in Xinjiang. There were more obvious time lags in the response of changes in total water storage to precipitation than for the changes in soil moisture. The changes in the normalized difference vegetation index from 2003 to 2013 indicated a slight greening, and the accumulated normalized difference vegetation index anomalies also increased sharply after 2008. There were significant increases in the Tianshan Mountains, Altay Mountains, and around the Tarim Basin, especially along the Tarim River. The results suggested that the changes in total water storage and soil moisture were regarded as better indicators of the vegetation dynamics than other hydro-climatic variables in Xinjiang. Climate warming has led to accelerated glacier shrinkage and snow melt, and the increased runoff is likely to lead to more infiltration of surface water into the soil and ground, resulting in increased total water storage.