In a recent paper in Science of The Total Environment, a team of Chinese researchers created a model of the Urumqi No. 1 catchment in Xinjiang, China, and made a surprising discovery. As they sought to estimate the effects of global warming on glacier thinning, retreat and local supply of water resources, they found that the glacier is expected to reach “peak water,” with runoff shrinking by half of its 1980 extent in the next 30 years. The glacier will also lose approximately 80 percent of its ice volume.
As glaciers shrink, runoff increases (with more melting) but then decreases thereafter when the size of the glacier has permanently decreased. Peak water, or the tipping point of glacier melt supply, when runoff in glacier-fed rivers reaches the maximum, is estimated to occur around 2020. This phenomenon shares its concept with the term “peak oil,” which refers to the hypothetical point in time when the global oil production rate will reach maximum capacity. Thereafter, oil production will only decline.
In contrast to peak oil, glacial reserves can be estimated with a higher certainty. Annina Sorg, an independent researcher with expertise in geomorphology, geography and climatology, explained the concept to GlacierHub. “Peak water for a catchment can be assessed with quite good precision if the past climate and glacial volume loss are well known and if reasonable climate models are being used,” she said. This is because, unlike oil, consumption of glacier meltwater does not have a direct impact on glacial melting. Glaciers will continue to melt no matter if the demand for glacial meltwater is high or low.
“Peak water is an important aspect of glacial impact of hydrology, and the term absolutely makes sense,” Matthias Huss, a senior lecturer from the University of Freiburg, expressed in an interview with GlacierHub. “After peak water, annual runoff sums from glaciers will be steadily decreasing, which might cause problems with water availability.”
Huss’s team recently published a paper on the first complete global assessment of when peak water from glaciers will occur. Huss believes the smaller scale study on the Urumqi glacier uses a very similar approach as he did for all 200,000 glaciers globally but with more accurate data for calibration and validation to fit the local context. Both studies also yield consistent findings.
In the arid regions of Central Asia, meltwater from glaciers determine streamflow. Glaciers are not only valuable water sources for the communities around rivers, but can also serve as buffers against droughts during dry periods.
“Conditions are ‘good’ before peak water— we even have more water than in the case of balanced glacier mass budgets. This water can be used for irrigation or hydropower production. However, after peak water, less water is available, most importantly in the summer months, which might have considerable impact on water resource management,” Huss warned.
The story is also more complex in a broader context. Whether water shortage is experienced due to glacier recession strongly depends on the climate regime. In general, glaciers play a more important role when summer climates are dry, as in the case of Xinjiang. Peak water also strongly varies with glacier size, with larger glaciers experiencing later peaks than smaller glaciers.
“As Urumqi Glacier is a relatively small glacier, it might not be fully representative for regional peak water, which is governed by the larger glaciers,” Huss explained.
Still, Sorg holds the view that the abundance of meltwater before peak water “might slow down a society’s attempts to elaborate mitigation measures, which would be needed to handle the second period of decreasing meltwater runoff.”
In the case of Xinjiang, runoff from glacier melting will likely experience a dramatic decrease from 2020 to 2050, post peak water. The east and west branches of Urumqi No. 1 Glacier also have different responses to climate change. By the end of the 21st century, as compared to 1980 rates, the area extent and ice volume of the west branch could decrease by up to 58 and 82 percent, respectively. While at the east branch, glacier area could shrink by 95 percent, losing about 99 percent of its ice volume.
“In my opinion, it is important to spread the term ‘peak water,’ also in popular media, not science alone. It draws awareness to the point that the depletion of glacial reserves is not a continuous process like emptying a bathtub,” Sorg told GlacierHub. Rather, peak water is a period of abundance that Sorg thinks is probably not appreciated enough and is taken for granted.
Sorg concluded with a somber reminder. “After peak water, the days of plenty are over— at least in respect to glacial meltwater availability,” she said. As Xinjiang is very dependent on its glaciers, mitigation measures are required to adapt to glacier mass changes for long-term water security in the region.