Seasonal Lake Changes on the Tibetan Plateau

Posted by on Jan 31, 2017

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Kunlun Mountain Chains (source: Yunsheng Bai / Flickr).

Kunlun Mountains (source: Yunsheng Bai/Flickr).

The Kunlun Mountains, featured as a mythical location in the legendary Chinese text Shanhai Jing, are one of the longest mountain chains in Asia. From the Pamirs of Tajikistan, the mountains run east along the border of Xinjiang and Tibet to the Qinghai province, forming part of the Tibetan Plateau. A number of important glaciers and lakes are found in the area, attracting glaciology researchers to the region throughout the year. Yanbin Lei, an associate research fellow at the Chinese Academy of Sciences, is one scientist conducting important field work in the region.

Recently, Lei et al. published a paper  in the American Geophysical Union Journal Geophysical Research Letters that describes how lakes in the Tibetan Plateau are growing and deepening due to climate change. In particular, the scientists identified two patterns of lake level seasonality.

Because the climate is warming, an earlier melt and a relatively large increase in spring runoff are observed for all scenarios. This in turn increases water availability in the Indus Basin irrigation scheme during the spring growing season, according to Lei et al. This finding projects that rainfall will increase, according to another study by Su er al. In addition,  the discharge in the major large rivers of South and East Asia will also increase.

Kotra Tso at the Kunlun Mountains (source: Dr. Yongjie Wang).

Kotra Tso at the Kunlun Mountains (source: Yongjie Wang).

“Though crucial, the paucity of instrumental data from the sparsely populated Tibetan Plateau has limited scientific investigations of hydroclimate response to recent climate change,” Lei told GlacierHub. The Tibetan Plateau has a large spatial coverage and high elevation (the average latitude is over 4000 meters), not to mention an incredibly harsh climatic condition, which makes conducting research and taking measurements difficult. Because the seasonal dynamics of the lakes is not sufficiently understood, the research conducted by Lei et al. in the Tibetan Plateau was unprecedented.

“In general, there is a lack of monitoring of lake levels in the Kunlun Mountains, and consequently, data is missing for the lakes,” Lei  added. “Even if remote sensing were developed as a major method for studying inter-annual changes of lakes, the accuracy and frequency of this method would still be limited to study seasonal changes.”

With the help of “situ observations,” Cryosat-2 satellite altimetry data between 2010 and 2014, and Gravity Recovery and Climate Experiment (GRACE) data, Lei et al. managed to identify two patterns of lake level seasonality. “In the central, northern, and northeastern Tibetan Plateau, lake levels are characterized by considerable increases during warm seasons and decreases during cold seasons, which is consistent with regional mass changes related to monsoon precipitation and evaporation,” Lei et al. describe in their paper.  “In the northwestern Tibetan Plateau, however, lake levels exhibit dramatic increases during both warm and cold seasons, which deviate from regional mass changes.”

In an interview with GlacierHub, Lei summarized the reasons for this finding: “The difference was mainly caused by the glaciers and precipitation. There are widespread glaciers in the northwest Tibetan Plateau and the area of glaciers is larger than the area of lakes. The precipitation in summer is also low, resulting in high spring snowfall and large summer glacier melt to feed the lake. Meanwhile, in the northern Tibetan Plateau, there are fewer glaciers but more summer rainfall, causing an increase in the lake level,” Lei told GlacierHub.

The location of the selected lakes in the NWTP, NTP, CTP, and NETP (source: Lei et al. / Wiley).

The location of the selected lakes in the NWTP, NTP, CTP, and NETP (source: Lei et al. /Wiley).

Additionally, the seasonal difference of precipitation is also important. Annual precipitation in the northern Tibetan Plateau is 300-400 mm with 90 percent of precipitation occurring in summer, according to Lei. Annual precipitation in the northwest Tibetan Plateau is about 200 mm because spring snowfall counts more. “The lake level responses to different drivers indicates heterogeneous sensitivity to climate change between the northwestern Tibetan Plateau and other regions,” Lei noted.

As Lei et al. demonstrate in their study, climate change has dramatically influenced the lakes and rivers of Tibet. Higher temperatures saliently have led to the expansion of the watershed. However, Lei is unsure about the exact effect of climate change.

“Since 2006, lakes in the central Tibetan Plateau have been stable, while lakes in the northern Tibetan Plateau and Northwest Tibetan Plateau are growing at a high speed,” he said. “When these lakes will reach equilibrium remains uncertain.”

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