Are the shelterbelts in the “Three Norths” planted in vain? No, because the sandstorms are “cheating”

Basically every spring, people living in the north will experience a few sandstorms.

However, every time a sandstorm hits, some people will ask, "Don't we have the 'Three Norths' shelterbelts? Why are there still sandstorms?"

In the past few decades, the most representative and effective windbreak and sand fixation project in my country is the construction of the "Three Norths" shelterbelt. This project has played a very positive role in fixing sand in the domestic sand source areas and reducing the harm of sandstorms. Statistical results show that the average number of sandstorm weather processes in my country has dropped sharply from 27 times in 1961-1989 to 4 times in 2011-2020.

“Three Norths” Shelterbelt

The "Three Norths" shelterbelt refers to a large-scale artificial forestry ecological project built in Northwest, North China and Northeast my country. The project is planned to be built in three phases and eight stages from 1978 to 2050. It mainly increases the forest coverage rate through desertification control, returning farmland to forests and returning pasture to grassland. It is expected to afforest 35.083 million hectares and increase the forest coverage rate in the Three Norths from 5.05% to 15.95%. The "Three Norths" project aims to improve the local ecological environment, mitigate ecological disasters caused by drought, wind and sand hazards and soil erosion, and also build an artificial barrier against wind and sand.

Schematic diagram of the Three North Shelterbelt Area and its land use and cover (Source: Huang et al. 2020)

A paper published in Nature Sustainability in 2019 stated that satellite observations showed that in the past two decades, China, which accounts for only 6.6% of the world's vegetation area, contributed 25% of the global increase in leaf area index (LAI, in short, the sum of leaf areas in a certain area), with the increase in forest cover being the main contribution. The Three Norths Project has contributed greatly to the increase in the leaf area index.

Trends in average leaf area index (LAI) from 2000 to 2017

(Source: Chen et al. 2019)

However, why is it that such a large-scale afforestation project is still unable to completely resist the invasion of severe catastrophic weather such as sandstorms?

Before answering this question, we need to understand how sandstorms are formed.

Part 1

How are sandstorms formed?

There are three necessary conditions for the occurrence of sandstorms - sand sources, unstable atmospheric stratification and strong wind conditions.

1. Sand source

my country's northwest region is far from the ocean, with little precipitation and extremely high evaporation, creating a large area of ​​desert Gobi represented by the Taklimakan Desert. At the same time, my country is backed by the vast arid and semi-arid areas of the Mongolian Plateau, which are important sources of sandstorms in northern my country. Taking Beijing and Tianjin as an example, the transmission of sandstorms can be summarized into three types: north route, west route and northwest route.

Transmission paths of sandstorms affecting Beijing and Tianjin

(Source: China Weather Network)

2. Unstable atmospheric stratification

What is atmospheric stratification? In short, it is the vertical distribution of physical quantities such as atmospheric temperature and humidity. These factors together determine the vertical stability of the atmosphere.

Every spring, the land in the Northern Hemisphere begins to warm up. The precipitation in the sand source areas is generally low, the vegetation coverage is very low, and the soil conditions are loose. Since the soil has a relatively small specific heat capacity, the surface temperature rises quickly, so in the vertical direction, it is easy to form a spatial distribution with high air density in the upper layers and low density in the lower layers . This makes the atmospheric stratification very unstable, which easily causes vertical convection, and the sand and dust are naturally lifted from the surface into the air.

3. Strong wind conditions

How did the dust get transported to us from thousands of miles away? This brings us to the Mongolian cyclone, one of the dominant weather systems in spring in my country and the driving force behind the dust weather.

When cold air moves in winter and spring, the originally stable mid-latitude westerly belt will experience obvious fluctuations, generating northerly winds that carry cold air southward. At the same time, a counterclockwise rotating temperate cyclone will form in the eastern part of the northerly zone (it is named the Mongolian cyclone because it is generated and active on the Mongolian Plateau, and its horizontal range can reach 2,000 to 3,000 km). The stronger the cold air, the stronger the north wind will be, and the stronger the cyclone will usually be. The Mongolian cyclone can carry sand and dust from the sand source to an altitude of more than 2 km, accompanied by strong northerly winds, all the way south.

Satellite cloud image of a severe sandstorm in 2021. The cloud system rotating counterclockwise on the right is the Mongolian cyclone. The sand and dust in the clouds can be clearly seen (Image source: China Meteorological Administration)

It can be seen from this that if the source of the sandstorm weather is not the area where the shelterbelt is located (that is, external input), even if there are shelterbelts, their role will be just a drop in the bucket in the face of 2km high sandstorm transmission.

Part 2

Why have sandstorms become more frequent in recent years?

Entering the third decade of the 21st century, the frequency of sandstorms in my country seems to have increased again.

For example, in 2021 and 2023, my country experienced 13 and 11 sandstorm weather events respectively, both far exceeding the average state from 2011 to 2020, and their intensity also increased.

Professor Chen Wen's team at Yunnan University used the hybrid single-particle Lagrangian integral trajectory model (HYSPLIT) to trace the sources of sand during the 11 rounds of sandstorms that affected Beijing in 2023, and found that most of the sandstorms were external inputs, with the Mongolian Plateau being the main source of sand.

Schematic diagram of the reverse trajectory of 11-day sandstorm weather at 1 km height in Beijing in 2023 (Reference: Piao et al. 2023)

The increase and intensification of sandstorm weather processes can actually be attributed to the following factors.

1. Natural factors

The frequent dust storms in northern China may be related to the change in the strength of the East Asian winter monsoon. The resurgence of dust storms since 2021 may be related to the East Asian winter monsoon entering a strong cycle again. When the East Asian winter monsoon becomes strong, cold air activities usually become active, which can easily lead to stronger northerly winds.

Another reason is the alarming warming rate of the Mongolian Plateau. In the general debate of the 74th session of the United Nations General Assembly in 2019, Mongolian Foreign Minister Tsogtbaatar pointed out: "As a landlocked developing country, Mongolia has suffered the catastrophic impact of climate change while making little contribution to global warming. In the past 80 years, the average annual temperature in Mongolia has risen by 2.26℃. In the past 40 years, the area of ​​permafrost in Mongolia has shrunk by more than two times, and more than 800 lakes have dried up." This warming rate is more than twice the global average.

In recent years, some studies published in top international journals such as Nature and Science have shown that the degree of warming and drying of the Mongolian Plateau may have reached or even exceeded the critical point - the threshold at which the regional climate changes from one equilibrium state to another. When the critical point is exceeded, regional climate change tends to change suddenly and irreversibly.

Surface air temperature changes on the Mongolian Plateau (MP) were calculated based on multiple sets of reanalysis data. (a) Spatial distribution of summer temperature trends in the MP from 1986 to 2004 (unit: °C per decade). (b) Nine-year moving average sequence of regional average temperature anomalies in summer in the grey box (relative to the average from 1981 to 2010). (c) Frequency distribution of average summer temperature anomalies on the MP every 20 years from 1861 to 2020. (Source: Cai et al. 2024)

Warmer and drier regional climates are usually accompanied by less precipitation. The Mongolian Plateau has less precipitation and higher temperatures in spring. Due to the lack of soil moisture, the near-ground temperature is cooled by evaporation. The atmosphere and soil will make the ground temperature higher through the "land-air feedback" effect, thereby enhancing the instability of the atmospheric stratification and creating good lifting conditions for loose soil.

2. Human Factors

In addition to natural factors such as climate change, land desertification caused by human factors is also a factor that cannot be ignored. Due to scarce precipitation, Mongolia is basically dominated by an arid and semi-arid climate, and the vegetation types are mainly temperate grasslands and desert Gobi. Therefore, animal husbandry is one of the country's pillar industries, and the livelihoods of more than 80% of the rural population are basically completely dependent on natural conditions.

Large-scale animal husbandry has also had a serious impact on the local ecological environment. According to statistics, from 1990 to 2020, the number of livestock in Mongolia has increased from more than 20 million to nearly 70 million, a number that has far exceeded the ecological carrying capacity. As a result, 77% of the country's territory is suffering from varying degrees of desertification and land degradation.

Changes in total livestock population in Mongolia

(Image source: International Monetary Fund)

3. The role of domestic sand transport is also worthy of attention

Although Mongolian desertification is the main source of sand for China's sandstorms, objectively speaking, the contribution of domestic sand sources such as the Turpan Basin cannot be ignored. The team of Academician Huang Jianping of Lanzhou University used the concentration weight trajectory analysis method to quantify the contribution of different sand sources to 10 sandstorms in northern China in 2023. The results show that the average contribution of the Mongolian Plateau to sandstorms in northern China is about 42%, but the average contribution of the Taklimakan Desert is also 26%.

In general, the "Three Norths" project can play a good role in fixing local sand sources and reduce the frequency and intensity of sandstorms to a certain extent. However, sandstorms are a natural phenomenon, and humans do not have the ability to completely eliminate such disastrous weather at present, but can only slow it down and adapt to it.

In addition, we should have a deeper understanding that as a naturally existing ecosystem type, blind management of desert Gobi will instead ignore regional suitability and the carrying capacity of water and soil resources, leading to some unsustainable phenomena.

Part 3

Fighting sandstorms requires joint efforts

Just as the last round of sandstorms arrived in Beijing after a long journey, the top international academic journal Nature published a news report on April 15 about Chinese scholars using artificial intelligence (AI) to predict the sandstorm weather process. The report introduced that the team of Academician Huang Jianping of Lanzhou University used a large amount of existing sandstorm weather data and developed a sandstorm spatiotemporal evolution forecasting system with the help of AI. In the trial operation in 2023, the error rate of the system was 13% lower than that of the non-AI model. Humans have one more technological means to deal with sandstorms.

However, we should also see that in addition to China, many Asian countries are also threatened by sandstorms every year. Sandstorms not only bring inconvenience to people's lives, but also affect our health. Therefore, the prevention and control of sandstorms has always been an international research hotspot, but it is also a global problem.

In an interview, Wang Zifa, a researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, said that desertification mostly occurs in remote and economically underdeveloped areas. Using scientific means to alleviate sandstorms requires a solid foundation of human and material resources as well as extensive attention and support from the government and people from all walks of life.

Against the backdrop of global warming, the control of sandstorms also requires the promotion of international cooperation. In November 2022, Chinese President Xi Jinping proposed in a meeting with Mongolian President Khurelsukh that he hoped to discuss with Mongolia the establishment of a "China-Mongolia Desertification Control Cooperation Center" to provide Mongolia with Chinese technology and experience in desert control and balance ecological protection and economic development in the sandy areas.

Hopefully, with active and effective international cooperation, combined with the development of the sand and dust forecasting technology mentioned above, people will be able to better mitigate and adapt to extreme climate change in the future and protect our home planet.

References:

[1]https://www.nature.com/articles/d41586-024-01076-7 Lethal dust storms blanket Asia every spring — now AI could help predict them

[2]Duan, H., Hou, W., Wu, H., Feng, T. & Yan, P. Evolution Characteristics of Sand-Dust Weather Processes in China During 1961–2020. Front. Environ. Sci. 10, (2022).

[3]Huang, T., Pang, Z., Yang, S. & Yin, L. Impact of Afforestation on Atmospheric Recharge to Groundwater in a Semiarid Area. Journal of Geophysical Research: Atmospheres 125, e2019JD032185 (2020).

[4] http://www.forestry.gov.cn/c/sbj/gcjj/501731.jhtml Introduction to the Three North Shelterbelt System Construction Project.

[5]Chen, C. et al. China and India lead in greening of the world through land-use management. Nat Sustain 2, 122–129 (2019).

[6]Piao, J. et al. Increased sandstorm frequency in North China in 2023: Climate change reflection on the Mongolian plateau. Innovation 4, (2023).

[7] http://www.news.cn/talking/2023-04/14/c_1212086349.htm Why are sandstorms so frequent this year?

[]8https://news.un.org/zh/story/2019/09/1042632 [General Debate of the United Nations General Assembly] Mongolian Foreign Minister Tsogtbaatar

[9]Zhang, P. et al. Abrupt shift to hotter and drier climate over inner East Asia beyond the tipping point. Science 370, 1095–1099 (2020).

[10]Cai, Q. et al. Recent pronounced warming on the Mongolian Plateau boosted by internal climate variability. Nat. Geosci. 1–8 (2024)

[11]https://wapbaike.baidu.com/tashuo/browse/content?id=b699ee53431386862bfa14c9 Behind the Mongolian sandstorm: Overgrazing for cashmere exports

[12]Chen, SY, and Coauthors, 2023: Mongolia Contributed More Than 42% of the Dust Concentrations in Northern China in March and April, 2023, Adv. Atmos. Sci.

[13]https://chinadialogue.net/zh/3/107461/ Under the influence of sandstorms, China and Mongolia are promoting cooperation in desertification control