Increased Discharge in the Tianshan Glacierized Watersheds

Western Tianshan Mountains in Xinjiang, China, overlooking the glacier-fed Sayram Lake (Source: Jaymar Alvaran/Creative Commons).

In the arid and semi-arid regions of Central Asia, including western China, the glaciers of the Tianshan Mountains are an important water source for the inhabitants of the area. But accelerated glacier retreat is an unfortunate product of the changing climate, and the Tianshan glaciers are no exception. A recent study published in Hydrological Processes by Chinese scientists Min Xu, Hao Wu and Shichang Kang explored how the glacierized watersheds of the Tianshan Mountains have changed over almost 60 years.

Home to some 8,000 glaciers and spanning across approximately 7,200 square kilometers, the Tianshan Mountains are among the largest mountain systems in the area as well as a “water tower” of Central Asia. According to the study, the snow and glaciers yield 40 to 70 percent of the total river discharge of the region, feeding the water that supplies approximately 50 million people in Kyrgyzstan, Uzbekistan, northern Tajikistan, and the Xinjiang province of western China. The researchers used non-parametric tests and wavelet transforms to assess the changes of temperature, precipitation, discharge, glacier volume and runoff of six various watersheds of the Tianshan from 1957 to 2004, ultimately examining how different rivers have responded to climate change.

The study concluded that the glacierized region of the Tianshan Mountains has undergone significant change in the past several decades and that “regional climate warming was obvious.” Additionally, they found patterns in the results. For temperature, “the warming trend increased gradually from east to west, and the increase in temperature was greater on the north slope than on the south slope,” according to the paper. The results mentioned similar patterns for precipitation. From the eastern to central region, the trend increased but was followed by a trend decrease from central to western. However, despite the decline, the value in the west was still higher than in the east. As for the discharge, it also generally increased from east to west. Lead scientist Min Xu explained to GlacierHub that the main reasons for the differences in trends across the regions are the variations in precipitation and glacier area, which are generally larger in the west. This pattern reflects the predominant atmospheric circulation, which comes from the west; the moisture-bearing winds deposit the largest amount of precipitation on the first mountains which they encounter.

Image of the Tianshan Mountains (Source: travelingmipo/Creative Commons).

One of the significant concerns regarding the increase in glacier discharge is how the waters supported by Tianshan Glacier meltwater stand concerning the peak water value—as glacier retreat advances, rivers first carry more water, reflecting the more rapid melting, but then later have lower flow, because the glaciers are depleted.

Although this study does not address the concept of peak water directly, it does report on three highly relevant points. First, there is an overall upward trend across the six discharge locations. These results thus indicate that the calculated trends are currently pre-peak value. Second, the patterns do vary from river to river depending on the geography. For instance, where the exact position is in the mountains. Additionally, where on the individual mountains, whether the north or south slope or high or low elevation. These differences demonstrate the variability in predicting peak value. And third, not all glaciers are melting at similar rates and react to climate dynamics differently. Many higher glaciers have remained relatively stable regarding discharge variability. But scientists do expect even the upper glacier watersheds to exhibit more substantial fluctuations as glaciers will shrink under a warming climate.

Such a phenomenon will have broad ramifications across the region. “Changes in the spatial and temporal distribution of water resources due to climate change will lead to unbalanced developments in the productivity of the region, which would aggravate discrepancies of the economy,” glaciologist Shiqiang Zhang of Northwest University in China told GlacierHub. “It is very important to evaluate the fluctuations of glaciers and water resource changes on the watershed scale under the changes in climate, which not only provides references for assessing the changes of water resources in future, but also provide important suggestions for water management in Central Asia.”

Image of a glacier-fed river feeding into Ala-Kul Lake deep inside the Tianshan (Source: Journeys On Quest/Creative Commons).

Hongkai Gao, postdoctoral research associate at the Julie Ann Wrigley Global Institute of Sustainability at Arizona State University, shared his remarks on the importance of the study. “It is essential to study runoff changes of glacier-fed watersheds in different climatic regions of the Tianshan Mountains,” Gao told GlacierHub. “This study helps us to gain a better understanding on the recent changes in the Central Asian ice cover with regard to the ongoing climate change and for the assessment of the contribution of the glaciers’ meltwater to the total runoff.”

However, the concerns go beyond Central Asia. “The hydrological implications of climate change are a global concern,” Xu told GlacierHub. Melting glaciers across the world face changes in discharge and face peak water value. Once this peak water value has passed, “water resources are expected to diminish in glacier-fed watersheds, and significant economic and societal impacts are expected in peripheral regions,” Xu elaborated. “Therefore, we evaluate the fluctuations of glaciers and water resource changes on the watershed scale under the past climate change. This work will help us to understand the changes of runoff in future climate change and provide the references for adopting policies for water resource management.”

Adopting sustainable water resource policies now could partially offset the potential threat towards local peoples’ livelihoods and well-being to occur in the decades to come as a result of melting glaciers. Researching and understanding the trends, as these scientists did for the Tianshan, is the crucial first step to making effective policies.