Hydrological processes for rivers fed predominantly by snow and glacier meltwater will be more complex under global warming scenario. Tienshan Mountains, "water tower of Central Asia", provide the source of many transborder rivers that bring fresh water to more than 100 millions of people.
Researchers from the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences revealed recent changes in water discharge in snow and glacier melt-dominated rivers in the Tienshan Mountains, Central Asia.
They conducted a systematic analysis of runoff changes in two contrasting headwater rivers - Toxkan River (with glacierized area of 3.66%) and Kumalak River (with glacierized area of 16.34%) - from 1990 to 2015, as well as a comprehensive analysis to estimate potential reasons for their changes.
These included temperature, precipitation, and altitude of the 0 °C isotherm, snow cover area and snow depth, as well as glacier mass balance according to statistical mechanics and the maximum entropy principle (SMMEP) model and the sensitivity model.
In addition, they also discussed the impacts of these drivers on hydrological processes in different spatial and temporal, looked for potential links, and examined responses to the drivers' variabilities.
The researchers found that for the Toxkan River, the decrease in spring runoff mainly resulted from reductions in precipitation, whereas the decrease in summer runoff was mainly caused by early snowmelt in spring and a much-reduced snow meltwater supply in summer. In addition, the obvious glacier area reduction in the catchment (decreased to less than 4%) also contributed to the reduced summer runoff.
For the Kumalak River, a sharp decrease rate of 10.21 × 108 m3/decade in runoff was detected due to summertime cooling of both surface and upper air temperatures. Reduced summer temperatures with a positive trend in precipitation not only inhibited glacier melting but also dropped the 0 °C layer altitude, resulting in a significant increase in summertime snow cover area and snow depth, a slowing of the glacier negative mass balance, and a lowering of the snow-line altitude.
The study was published in the journal of Remote Sensing.
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