The Change of Water Budget and its Causes in Drylands of China

Abstract:

Abstract: The drylands of China serve as ecological security barriers, whose ecological environment is fragile and suffers severe problems of desertification at present. Some recent studies pointed that the drylands in northwest China are getting wet, which turns out to be significant for the regional ecosystem and human survival environment, as well as the projections of future climate change. In this study, the precipitation, evapotranspiration, runoff, water vapor convergence and other water cycle processes in drylands of China over the past four decades (1980-2019) are investigated. The atmosphere-land water balance equation in drylands of China is established according to three sets of precipitation observation datasets (PREC/L, GPCC, CRU), five existing reanalysis datasets (MERRA2, NCEP2, CFSR, ERA5, JRA55) and GRACE datasets. By integrating various datasets, the equation’s budget items get closed, thus the basic orders of the water cycle processes including precipitation, evapotranspiration, runoff and water vapor convergence are provided. Meanwhile, changes of all processes in the past 40 years are analyzed, and the differences between the east and the west of drylands are compared. The results demonstrate that the total precipitation and the average evapotranspiration increased, the total runoff decreased over the past 40 years in the drylands of China. Though the total precipitation and water vapor content in the atmosphere have increased, the west and east of drylands present opposite trends. Generally, the water cycle is accelerated in the drylands of China over the past 40 years. Despite of this, the increase of precipitation fails to balance the water consumption due to evapotranspiration, resulting in a significant decrease of water storage in drylands.