Recent Changes in Water Discharge in Snow and Glacier Melt-Dominated Rivers in the Tienshan Mountains, Central Asia

Abstract

Global warming has generally led to changes in river runoffs fed by snow and glacier meltwater in mountain ranges. The runoff of the Aksu River, which originates in the Southern Tienshan Mountains, exhibited a positive trend during 1979–2002, but this trend reversed during 2002–2015. Through a comprehensive analysis, this study aims to estimate potential reasons for changes in the runoff of its two contrasting headwaters: the Toxkan and Kumalak Rivers, based on climatic data, the altitude of the 0 °C isotherm, glacier mass balance (GMB), snow cover area (SCA), snow depth (SD) and the sensitivity model. 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 SCA and SD, a slowing of the glacier negative mass balance, and a lowering of the snow-line altitude.

Spatio-Temporal Development of Vegetation Carbon Sinks and Sources in the Arid Region of Northwest China

“…Li et al [ 34 ] found that the vegetation in the Tienshan Mountains of NWC is extremely vulnerable and sensitive to water deficits. Recent studies showed that the temperatures in the mountains are warmer than the lower plains [ 50 , 51 ], which has aggravated the melting of water from glacier and snow [ 52 , 53 ]. Under the influence of climate change, the river runoff in the NWC from the glacier and snow meltwater has greatly increased [ 52 , 54 , 55 , 56 ], and this trend will continue.…”

Scientists’ warning of the impacts of climate change on mountains

“…Thus, the concept of sensitivity of the mountain cryosphere is multifaceted with the major control being temperature but precipitation and the properties of the land surface also being important. Sensitivity of the mountain hydrosphere is usually described in terms of changes in river runoff in response to climate change (including temperature, precipitation, and snow/ice melt) ( Shi & Durran, 2014 ; Zhang et al, 2020 ). Different measures of this ‘sensitivity’ have therefore been used, including peak, seasonal or annual discharge variations, varying snow/glacier melt contributions, timing of peak flow, groundwater recharge etc .…”

“…Different measures of this ‘sensitivity’ have therefore been used, including peak, seasonal or annual discharge variations, varying snow/glacier melt contributions, timing of peak flow, groundwater recharge etc . ( e.g ., Barnhart, Tague & Molotch, 2020 ; Zhang et al, 2020 ). This means that calculations of hydrosphere ‘sensitivity’ are location-specific and may not be comparable to other mountain river systems.…”

Variability of the precipitation over the Tianshan Mountains, Central Asia. Part II: Multi‐decadal precipitation trends and their association with atmospheric circulation in both the winter and summer seasons

“…Rapid warming accelerates the melting of glaciers, snow, and permafrost, thereby affecting the regional water cycle and causing changes in the amount of runoff and the ground water recharge (Aizen et al ., 2006; Farinotti et al ., 2015; Chen et al ., 2019). Glacial shrinkage will provide sufficient water in the form of increased glacial runoff for a short period (Hagg et al ., 2006; Shahgedanova et al ., 2020) but if temperatures continue to increase and precipitation remains constant or decreases in the future, continued glacier shrinking will eventually lead to a decrease in glacial recharge by solid precipitation and thus total runoff (Sorg et al ., 2012; Chen et al ., 2020; Zhang et al ., 2020). This is detrimental to the spatial distribution of water resources in Central Asia.…”