Runoff of almost all rivers in the arid regions of China’s northwest has shown a significant increasing trend, with the aggravation of global warming in the last half century. However, that of the Hotan River in China’s Xinjiang autonomous region showed an abnormal trend of slight decreasing contemporarily.
Scientists in Xinjiang Institute of Ecology and Geography (XIEG), Chinese Academy of Sciences have recently uncovered the reason for this unusual decreasing trend of runoff. Their research results were published on Atmospheric Science Letters.
Temperature rises cause increases in the melting of snow and glacier in mountainous areas, and have a significant effect on runoff, especially for rivers whose most runoff depends the snow or glacier melting. Many glaciers in the northwestern arid region continue to retreat, and lead to increase in river runoff.
“That makes it rather unusual for the Hotan River runoff decrease,” said CHEN Yaning, lead author of the study and also researcher of XIEG.
75 per cent of Hotan River’s annual runoff was determined by summer runoff. And the summer runoff was strongly associated with summer upper-air temperature and mountain land surface temperature during 1960–2009, according to CHEN.
Through analysis on data from the last half century, scientists showed that the decrease in mountain land surface temperature and upper-air temperature in summer are probably the main reason for the slight runoff decreasing trend in the Hotan River over the most recent 50 years.