Freshwater resources have always played a vital role in the development of human society, but with the impact of global warming and human activities, most of the lakes that store a large amount of freshwater resources are in a state of retreat in the world, but the lakes on the Qinghai-Tibet Plateau have unusually expanded significantly, does this mean that the shortage of freshwater resources has been alleviated?
Image source: Veer Gallery
This is not the case, on the contrary, the Tibetan Plateau may also face a huge disaster.
Zhang Guoqing, a researcher from the Environmental Change and Multi-Sphere Process team at the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences, systematically predicted the status of lakes on the Tibetan Plateau by 2100 (area, water level, water storage, etc.) through model simulation, field investigation and remote sensing monitoring, revealed a series of disasters that may be caused by lake expansion, and emphasized the need to develop effective strategies to reduce the harm caused by lake expansion.
At the same time, the study found that it is necessary to further protect biodiversity and ensure the safety of life and property of people living in this ecologically sensitive area, and the research results were published in the journal Nature Earth Sciences on May 27, 2024.
What are the challenges facing the Tibetan Plateau?
Water is the source of life, especially freshwater resources, which are extremely important for sustaining life on Earth, and at the same time affect the functioning of ecosystems and the economy of human society. Eighty-seven percent of the planet's available surface freshwater resources are stored in lakes, but the effects of global warming and human activities in recent decades have led to the retreat of most of the world's lakes, while the lakes on the Tibetan Plateau are expanding, which is not a good thing.
Lakes on the Tibetan Plateau (Credit: Science Bulletin)
The Qinghai-Tibet Plateau has the largest number of lakes in China (accounting for more than 50% of the country's lakes), and if only the lakes with an area of more than 1 km2 are counted, the number of lakes exceeds 1,400. In addition to lakes, there are large quantities of glaciers and permafrost, which are precious liquid (lake) and solid (glacial, permafrost) freshwater resources.
The rivers originating from the Tibetan Plateau provide a large amount of fresh water for the inhabitants of Southeast Asia, so the Tibetan Plateau is also known as the "water tower of Asia".
In recent decades, due to global warming, glaciers and permafrost on the Qinghai-Tibet Plateau will bear the brunt of the impact, and a large number of glaciers and permafrost will begin to melt, meltwater will enter the lakes, and the lakes on the Qinghai-Tibet Plateau will begin to expand.
While lake expansion and increased freshwater resources may lead to a greener and more livable environment, lake expansion will also have worse impacts: the continued expansion of lakes is leading to potential basin mergers or reorganizations, threatening the region's infrastructure and ecological security.
Lakes on the Qinghai-Tibet Plateau - Jieze Chaka (Image source: taken by the author)
It is obvious that lake expansion will pose serious natural and social problems, but how much will the lake expand in the future? What specific impacts will it have on the Tibetan Plateau? Although there have been some models for predicting lake changes in the past, previous studies have focused more on specific large lakes or single case studies, but have not been able to cover the overall changes in the entire plateau lakes and their broader impact on the entire Tibetan Plateau in the future.
To this end, a team led by Zhang Guoqing, a researcher at the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences, developed a generic data-driven modeling framework to address these issues, integrating the key drivers of lake area (precipitation, glacial meltwater, surface evapotranspiration, lake evaporation) and combining field surveys and remote sensing observations.
Under the Shared Socioeconomic Pathways (SSP) scenario, the team quantified the annual changes in the area, water level, and water storage of each endogenous lake from 2021 to 2100. Finally, the degree of impact on the reorganization of the lake basin, infrastructure and ecological environment was assessed.
In the next 80 years, the lakes of the Tibetan Plateau will expand significantly
According to Zhang's team, by 2100, under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 schemes (SSP1-2.6, SSP2-4.5 and SSP5-8.5 represent three different simulation schemes), the future surface area of inland lakes on the Tibetan Plateau is expected to increase to 53,657±5,068 km2 respectively (an increase of 52% compared with the lake area in 2020, equivalent to an increase of about 2,303 km2 per decade), 54,311±5,308 km2 (+54%, about 2,385 km2 increase per decade) and 58,716±6681 km2 (+67%, about 2,936 km2 increase per decade).
With the expansion of the lake area, it is expected that by 2100, the water level will rise by 10.21±4.14m (approximately 1.28m per decade) under the SSP1-2.6 scenario, 10.64±4.33m (approximately 1.33m per decade) under the SSP2-4.5 scenario, and 13.29±5.18m (approximately 1.66m per decade) under the SSP5-8.5 scenario.
Compared with the increase of lake area by about 11,400 km2 and the water level increase of about 5.25 meters from 2000 to 2020, respectively, the rate of lake surface area expansion and water level rise is expected to slow down significantly in the future. Over the next 80 years, lake water storage is expected to increase by 652.97±211 Gt (about 81.50 Gt per decade), 665.32±220 Gt (about 83.13 Gt per decade) and 908.44±282 Gt (about 113.50 Gt per decade).
The increase in lake water storage in the next 80 years is about 3.9, 3.9 and 5.4 times that of the increase in lake water storage between 2000 and 2020 under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios, respectively, and about 4-fold increase in water storage by 2100 compared with the period from the 70s of the 20th century to 2020.
The research of Zhang Guoqing's team shows that there is obvious heterogeneity in the spatial distribution of lake changes in the future. The greatest change is in the northern Tibetan Plateau, where the total area of lakes is expected to triple by 2100 under the SSP5-8.5 scenario.
Although the lake area in other regions has changed less than in the northern part of the Tibetan Plateau, the lake area in the southeastern, central, and northwestern inland Tibetan Plateau will also expand significantly (51%-71%). From the perspective of historical variation, the lake area in the southern part of the Tibetan Plateau showed a shrinking trend.
However, Zhang's team's research projections suggest that around 2021, lakes in the southern Tibetan Plateau will see a significant shift from contraction to expansion. There are significant differences in the evolution of lake surface area, water level and water storage.
During the period 2020-2100, the lake water storage (water level and area) varied from about 0.61 Gt (equivalent to 11.89 m and 8 km2) to 66 Gt (59 m and 903 km2). The increase in water storage in most lakes ranged from about 0.86 Gt (3.96 m and 7.83 km2, 25th percentile) to about 1.29 Gt (14.21 m and 47.14 km2, 75th percentile).
It is worth noting that Seringco (the largest lake in Tibet and the second largest lake on the Qinghai-Tibet Plateau; The largest lake on the Tibetan Plateau is Qinghai Lake) showed the greatest increase in water storage at about 66 Gt, and under the SSP2-4.5 scheme, the surface area of the lake increased by about 800 km2 and the water level increased by about 21 m.
Under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 schemes, by 2100, 70, 70 and 79 lake basins were reorganized into 28, 28 and 31 basins due to lake expansion. These lake-basin reconstitutions will occur mainly in the northern, eastern and southern parts of the Tibetan Plateau.
In addition, under the above three scenarios, 21, 19 and 23 lakes will be merged to form 10, 9 and 11 lakes, respectively. Lake consolidation is expected to occur mainly in the northeast and southeast of the Tibetan Plateau.
Expansion of lakes in different regions of the Tibetan Plateau by 2100 (Source: Nature Earth Sciences)
The serious consequences of lake expansion
To summarize the results of Zhang's team, by 2100, the lake area and lake water level of the Tibetan Plateau will increase significantly, especially the expansion of lake water storage in the northern part of the Tibetan Plateau, which leads to the reorganization of lake basins (mainly in the northern, eastern and southern parts of the Tibetan Plateau) and the merging of lakes (mainly in the northeast and southeast of the Tibetan Plateau). So what are the impacts of lake expansion, lake basin reorganization, and lake merging with each other on human society and natural ecology?
By the end of the decade, 1,023±281, 959±±274 and 1,481 km of roads will be submerged under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 simulation schemes, respectively. According to SSP2-4.5 (SSP1-2.6 and SSP5-8.5), about 118 km (149 km and 136 km), 215 km (264 km and 258 km) and 331 km (382 km and 390 km) of roads are expected to be at risk of flooding in 2030, 2040 and 2050, respectively. The flooded roads are mainly concentrated in the southern interior of the Tibetan Plateau.
Although the most significant lake expansion is expected to be inland in the northern part of the Tibetan Plateau, the presence of seasonal permafrost restricts road construction and human access, resulting in fewer flooded roads. Conversely, although less expansion of the lake is expected in the northeastern part of the Tibetan Plateau, a large number of road sections are expected to be inundated due to increased human activity and the popularity of roads near the lake.
On the scale of the lakes, 12 lakes (including the three largest lakes, Serinco, Namco, and Qinghai Lake) are considered to be the most potentially hazardous: the most flooded roads are near Serinco, and the length of the inundated roads is expected to reach about 84.13-119.08 km by 2100. Previously, due to the rapid expansion of Serinco, the S208 highway was washed away by floods at the end of September 2023.
There are almost all roads in the vicinity of Namtso, and under the three simulation schemes of SSP1-2.6, SSP2-4.5 and SSP5-8.5, it is estimated that about 73.27 km, about 34.02 km and about 118.91 km of roads will be flooded, respectively. Due to the significant expansion of Qinghai Lake, some roads in the northwest were flooded. According to SSP5-8.5, about 46.9 km of roads are expected to be flooded.
In conclusion, future lake expansion will lead to the potential risk of inundation of a large number of roads, which is a serious threat that should be considered in future rail and road planning.
Highway S208 near Serinco was washed away (Credit: Nature Geosciences; annotated as added by author)
Under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios, projections indicate that by 2100, an estimated 5.66 million, 7.4 million and 5.78 million people will live on the Tibetan Plateau, respectively, and that approximately 462, 458 and 615 settlements will be inundated, most of which are located inland in the southern part of the Tibetan Plateau.
In addition, 83 to 93 lakes are expected to inundate nearby settlements, with the most damage caused by Serinco, which will inundate between 64 and 81 settlements under various SSP scenarios. Some settlements are already facing flooding or are at greater risk, such as villages and buildings near Zarinam Mso Co.
A large number of settlements will be inundated (Credit: Nature Geosciences)
The village near Zhari Nam Mtso will be submerged (the yellow box is the original location of the village) (Image source: Nature Geosciences)
By 2100, the inundation area is expected to reach 8,533, 9,132 and 11,576 km2 under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios, respectively. Assuming that the livestock are evenly distributed, more than 500,000 head of livestock may be disturbed. In each SSP scenario, 4241±1168, 4459±1241 and 5968±1823 km2 of grassland will be submerged by 2100.
This will directly lead to a decline in livestock production, severely affecting the livelihoods of local herders and further exacerbating poverty levels. In their research, Zhang's team also identified 291 lakes on the plateau, which pose a serious threat to the safety of the grasslands. The loss of farmland can disrupt food production, affecting local food security and regional agricultural economies.
Grasslands are in danger of being submerged (Credit: Nature Geosciences)
In addition, glacial meltwater entering the lake leads to a decrease in lake salinity, altering the local lake ecosystem, causing species loss and biodiversity destruction. The expansion of the lake has led to changes in hydrology and landform, such as the outburst of Zhuo Nai Lake (one of the main calving grounds of Tibetan antelope) in 2011, which blocked the migration route of Tibetan antelope and greatly affected the survival and reproduction of Tibetan antelope. From a socio-economic perspective, based on the investment costs in 2022, the direct economic loss caused by road flooding by 2100 is estimated at RMB 20 billion to RMB 50 billion under the SSP2-4.5 projection scenario.
epilogue
Given the current context of global warming and climate change, a comprehensive understanding of future lake changes on the Tibetan Plateau is essential for effective water management, mitigation of hazards, and ecological protection of this important region. Zhang's team's research provides a scientific guide for future planning and valuable insights into avoiding the devastating consequences of impending lake expansion.
With global warming and melting glaciers, the lakes of the Qinghai-Tibet Plateau will continue to expand in the future, and if not addressed, villages and roads will be submerged, causing a lot of economic losses. The already fragile ecological environment has been devastated, and biodiversity has been destroyed. Effective strategies are needed to avoid possible future hazards, while protecting biodiversity and safeguarding the well-being of the people living in this ecologically sensitive area.
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Producer: Popular Science China
Author: Zang Tonggang (Master student in paleoclimatology)
Producer: China Science Expo