The Taklamakan Desert is flooding! But how can a desert flood?

The Taklimakan Desert in Xinjiang was hit by floods . Water more than one meter deep spread onto the road, causing some vehicles to stall and become unable to pass. What surprised many people even more was that floods were not uncommon in the Taklimakan Desert.

Taklimakan Desert hit by floods | Xinjiang Radio and Television

However, in our impression, the desert is an extremely dry and water-scarce place, so how could it flood?

Where does water come from?

According to the Xinjiang Water Resources Department, since July 15, due to high temperature snowmelt and heavy rainfall, the Aksu River, Hotan River and Yarkand River, the source of the Tarim River in Xinjiang, have experienced floods one after another; the Aral River section of the main stream of the Tarim River (Aksu City) has experienced floods exceeding the warning water level, among which the Xinquman River section (Shaya County) and the Yingbaza River section (Luntai County) have successively experienced floods exceeding the guaranteed water level, and the high water level in some river sections has lasted for nearly 1 month. At present, the entire Tarim River is showing a slow water retreat trend.

These rivers that flood are not ordinary rivers, they are called "seasonal rivers". In summer, they are exactly the same as ordinary rivers; but in spring and winter, they will disappear due to lack of water supply, leaving only a dry river channel. The water source of this type of river mainly comes from the meltwater of glaciers and snow in nearby mountains; in addition, direct rainfall in the area where the river flows (especially short-term heavy rainfall in mountainous areas in summer) is also a relatively important source of water.

Seasonal rivers are marked as blue dotted lines on the map, which means they are seasonal rivers | Ministry of Natural Resources

The Tarim River, the largest seasonal river in China, and its tributaries pass through the Taklamakan Desert.

The Taklimakan Desert is located in the Tarim Basin, surrounded by the Tianshan Mountains, Kunlun Mountains and Altun Mountains on three sides. The Tianshan Mountains are mostly above 4,000 meters above sea level, while the Kunlun Mountains have an average altitude of more than 5,500 meters. Their peaks are covered with snow and glaciers all year round. Whenever the temperature rises, the melted snow will flow down the mountain and gather into a river.

The Taklimakan Desert in the middle is like a big colander that cannot hold water. The melted snowwater will "break off" as it flows. But in the high temperature of summer, the melted snowwater increases, and seasonal rivers have the opportunity to rush through the desert, connect with each other, and become a big river.

The white areas are all ice and snow, which melt and gather into seasonal rivers｜Google Earth

Therefore, once the temperature rises and it rains heavily, the large amount of melted snow and rainfall will instantly fill up the capacity of the seasonal river , far exceeding the rate of evaporation and infiltration into the desert, causing a "flooding in the desert" scene.

Multiple heat waves + heavy precipitation

The meteorological conditions in recent times have resulted in high temperatures and heavy rains, which is the direct cause of the floods in the Taklamakan Desert.

Over the past month, the continental warm high pressure/Qinghai-Tibet high pressure controlled the upstream mountainous areas (green circle in the figure below). Under its control, the temperature in the Tarim Basin and surrounding areas continued to be high, and there were many periodic heat waves. Under this influence, the amount of meltwater from ice and snow in the mountainous areas increased significantly, and flowed into the main stream in the basin through the source streams of the Tarim River. The flood peaks of multiple melting ice and snow continued to overlap, forming a long-term and wide flood peak that lasted for about a month.

The height field (contour lines) of the middle troposphere (500hPa, about 5500 meters high) from July 22 to August 20 and its anomaly relative to the same period of previous years (coloring) | Japan Meteorological Agency

From July 22 to August 20, the national temperature was normal compared with the same period in 1991-2020. Positive values ​​are higher, and negative values ​​are the opposite. It can be seen that the temperature in Xinjiang has increased significantly compared with the same period in 1991-2020. | National Climate Center

At the same time, the overall precipitation in the mountainous areas of the upper reaches of the Tarim River has also been higher recently. These rains quickly converged on the steep terrain, which had a certain impact on the flooding of the middle and lower reaches of the main stream.

Percentage of precipitation anomaly across China from July 12 to August 10 relative to the same period from 1991 to 2020｜National Climate Center

In recent decades, the temperature and precipitation in the Taklimakan Desert have been increasing. Moreover, this rainfall occurs quite concentratedly . In Xinjiang, where the average annual rainfall is only more than 100 mm, there will be more than 40 mm of rainfall in just three or four days. Judging from the distribution of rainfall throughout the year, this is not rain, but simply pouring water.

Heavy rainfall and high temperatures combined with melting snow have led to floods, which are not uncommon in Xinjiang in summer. From 2017 to 2021 alone, Xinjiang recorded more than 20 rainstorms and flash floods. In 2021, the Yuqi area of ​​Sinopec Northwest Oilfield was hit by a flood, nearly 50 exploration vehicles and 30,000 sets of equipment were flooded, and the flooded area reached more than 300 square kilometers.

Will global warming cause more and more desert floods?

Precipitation and high temperature heat waves in mountainous areas are the key factors that cause floods. Judging from these two factors, against the backdrop of global warming, there is a high possibility that subsequent flood events will increase .

Although global climate change does not necessarily lead to individual heat waves or extreme rainstorms, observations and simulations in recent decades have shown that the overall trend of increasingly severe and common extreme events is closely related to climate change .

The impact of climate change on the world lies not only in the increase in average temperature, but also in the significant increase in the overall deviation of temperature from normal . According to the sixth assessment report conducted by the Intergovernmental Panel on Climate Change (IPCC) of the United Nations in 2021, at present, when the global average temperature is 1°C higher than that in the second half of the 19th century, the frequency of high temperature heat wave events is about 2.8 times that in the second half of the 19th century; and if the global temperature rises further by 0.5°C, the frequency of high temperature events will be 4.1 times that in the second half of the 19th century .

Changes in the frequency and intensity of high temperature heat waves under different possible scenarios mentioned in the IPCC Sixth Assessment Report from 1850 to 1900 (baseline), the present (1°C above the benchmark) and the future｜IPCC

Why is climate change associated with an increase in the frequency of extreme events such as heat waves? A more widely accepted explanation is the albedo feedback mechanism : Under the current climate change, Arctic sea ice and high-latitude snow have melted significantly, and the exposed sea and land surfaces are darker than the previous ice surface, with a decrease in albedo, thereby absorbing more heat, resulting in greater warming in high-latitude regions than outside the Northern Hemisphere poles, and a narrowing of the temperature difference between the poles and the tropics.

According to the meteorological principle of thermal wind, the high-altitude westerly belt is driven by the temperature difference between the poles and the tropics, like a natural barrier between the poles and the equator, making it difficult for air masses on both sides to cross easily. When the temperature difference decreases, the intensity of the high-altitude westerly belt will weaken accordingly, and it will be easier for cold and warm air to "break through" the barrier and travel from south to north, which is more likely to cause more frequent extreme events in mid- and high-latitude regions .

From the perspective of precipitation trends, in recent years, especially since 2018, the Tarim Basin of the Tarim River and its surrounding areas have had significantly more precipitation .

Changes in precipitation from 2018 to 2023 relative to the 1981-2010 average

We are still uncertain whether climate change will have a long-term impact on floods in Xinjiang; however, some studies[3] suggest that by the end of the 21st century, Xinjiang will see a significant overall increase in temperature and precipitation ; if greenhouse gas emissions are higher (and human-induced warming is more severe), the impact will be even greater. This simulation also suggests to some extent that long-term climate change factors may lead to significant warming and wetting in Xinjiang, resulting in more summer floods.

Changes in the average annual temperature (a, unit: °C) and the average annual total precipitation anomaly percentage (b, unit: %) in Xinjiang simulated by CMIP6 multi-models (relative to 1995-2014) | Reference [3]

Floods cannot turn deserts into oases. On the contrary, the soil structure in desert areas is loose, and floods may cause severe soil erosion , destroying existing vegetation and affecting the growth of future vegetation. Under such rapid water force, broken rocks can easily be eroded into pieces and become fragments, which will make them more susceptible to weathering. For example, if the bottom of the wind-eroded mushrooms in the heart of the Taklimakan Desert is hit by floods, they will fall headfirst and slowly disappear in the sea of ​​sand. If severe floods occur for a long time, this force is even enough to change the shape of the mountain and form canyons.

This is also why the Xinjiang Meteorological Bureau is reminding everyone to guard against mudslides . If such a large amount of water rushes down from the mountain and is mixed with some rocks and mud, it will be no joke.

References

[1]http://www.igsnrr.cas.cn/cbkx/kpyd/zgdl/cndm/202009/t20200910_5692379.html

[2] Pu Zongchao, Zhang Shanqing, Li Jinglin, et al. Climate change in the Taklimakan Desert surrounding area over the past 47 years[J]. Chinese Journal of Desert Research, 2010, 30(2): 413.

[3] Dong Siyan, Shi Ying, Wang Pengling, et al. Prediction of warming and humidification trend of Xinjiang regional climate in the 21st century (2024). Desert and Oasis Meteorology, 1-13.

Author: Deep Thought, Wind and Cloud Dream

Editor: Mai Mai