Why does the runoff in Hotan River show a slight decreased trend in northwestern China?

Abstract

During the recent 50 years, in response to global warming, nearly all of the rivers in the arid region of northwest China have shown significant increasing trends in runoff. However, runoff in the Hotan River has shown a slight decreasing trend that corresponded to a rate of −0.18 × 108 m3/decade for the same period. Here, based on an analysis of runoff from mountain pass hydrologic stations and precipitation during 1960–2009, as well as measurements of upper-air temperature (UAT) from the Hotan sounding station (1960–2011) and MODIS land surface temperature (LST) of the mountainous area (2001–2011), we found that the annual runoff in the Hotan River was mainly determined (75%) by summer runoff. We also determined that the summer runoff was strongly associated (correlation coefficient: R = 0.78, p < 0.001) with summer UAT at 500 hPa and mountain LST (R = 0.69, p < 0.001) during 1960–2009. Because the largest proportion of runoff in the Hotan River stems from glacial meltwater, we suggest that the decreasing trends exhibited by the UAT in the mid-lower troposphere and the LST within the mountainous area in summer are the main reasons why runoff shows a slight decreasing trend over the past half century.