Water balance change and its implications to vegetation in the Tarim River Basin, Central Asia

摘要

The Tarim River Basin (TRB) is one of the most important areas in Central Asia, and also the largest inland river basin in China. The runoff largely originates from alpine mountains, mainly supplied by glacier and snow melting. It meets the demand of oasis and more broadly ecosystems while shaping them up. In this study, the spatio-temporal variations of water balance and vegetation (as measured by the normalized difference vegetation index, NDVI) in the TRB during 2003-2014 were investigated on the basis of multiple satellite observations together with an energy balance model. The interactions between hydrological factors were discussed. Considering that hydrological processes affect on terrestrial ecosystem, variations in vegetation were also analyzed correspondingly. The analysis suggest that water budget has changed in the TRB. By looking into all components in the budget, it is found that there is a slight decreasing trend in precipitation, but a significant decreasing trend in ET at a rate of 38.4 mm/10 a. Meanwhile, there are an evident decreasing trend in both GRACE satellite derived terrestrial water storage change (GRACE-TWS change) and Global Land Data Assimilation System simulated soil moisture change (GLDAS-SM change), at rates of -17.8 mm/a and -17.0 mm/a, respectively, while the ground water (GW) was stable. Overall, the water balance in the TRB is negative during the period. However, it shows a significant increasing trend in snow/ice melting that is discharged into the TRB. The interactions among hydrological variables indicated that the ET, GRACE-TWS change and GLDA-SSM change are strongly dependent on the monthly precipitation. However, a time lag of the GLDAS-SM change occurs influenced by precipitation, which is more obvious than one of the GRACE-TWS change. GW change shows a positive correlation with precipitation over 1-month lag and 2-month lag. The results suggest soil moisture in warm seasons (summer and autumn) are mainly affecting vegetation growth in the TRB. The vegetation in the TRB was greening, the areas of low NDVI (0-0.15) decreased by 18.1% during 2003-2014.