Deserts and climate change
Deserts, which occupy approximately 20 percent of the Earth's land surface, are sensitive ecosystems that are increasingly impacted by climate change. Characterized by low humidity, high temperature fluctuations, and variable precipitation, desert environments are vulnerable to alterations in rainfall patterns and temperature increases. Climate change poses significant challenges, as rising temperatures may intensify drought conditions and alter the availability of water sources crucial for both human and ecological systems.
Predictions regarding future climate impacts on deserts are complex and vary widely across different models. Some regions may experience increased monsoon precipitation, while others, like parts of the Sahara and southwestern United States, face the risk of severe drying. These changes could lead to shifts in vegetation patterns, increased sand mobility, and heightened competition for water resources. Additionally, the frequency and intensity of sand and dust storms have escalated, creating further challenges for desert communities.
Overall, climate change threatens to exacerbate existing vulnerabilities in desert regions, necessitating adaptive management strategies to address reduced water availability and heightened ecological pressures. Understanding these dynamics is essential for fostering resilience in both natural and human systems within these fragile environments.
Subject Terms
Deserts and climate change
Deserts cover some 26.2 million square kilometers, or about 20 percent, of the Earth’s land surface, mainly in the subtropical to midlatitudes. The importance of water to human and natural systems in deserts makes those systems very sensitive to climate changes affecting the amount, type, timing, and effectiveness of precipitation.
Background
Deserts are fragile environments, easily affected by natural and human disturbance. They are being affected by a rapidly growing and increasingly urban population that is dependent on scarce surface- and groundwater. The historical and observational record indicates the great natural variability of climates in these regions, including the occurrence of periodic severe and multi-decadal droughts.
Causes of Deserts
Desert climates are characterized by low humidity (except in cool, foggy coastal deserts such as the Namib and Atacama), a high daily range of temperatures, and precipitation that is highly variable in time and space. The most extensive deserts lie astride the tropics. Solar heating in equatorial latitudes gives rise to rising moist air, which then condenses, loses moisture as tropical rainfall, cools, and descends away from the equator. As the air descends, it warms and becomes very dry. This descending, dry air in the subtropical anticyclonic belts maintains arid conditions throughout the year. The effects of stable air masses are reinforced in some areas by mountain barriers, which block moist air masses (for example, the Himalaya and other mountain ranges prevent the penetration of the southwest monsoon to the Gobi and Takla Makan Deserts of central Asia). Deserts located on the west coasts of South America and southern Africa (the Atacama and Namib) owe their hyperarid climates to the influence of cold oceanic currents offshore. These currents reinforce the subsidence-induced stability of the atmosphere by cooling surface air and creating a strong temperature inversion.
Effects of Climate Change
The effects and potential effects of past and future climate change on deserts are many and are influenced by the topographic and climatic diversity of desert regions. Global climate models differ in their predictions of the direction and magnitude of future change in arid regions. In some areas—such as China, southeastern Arabia, and India—increased monsoon precipitation is predicted, but its effects may be offset by higher evaporation as a result of increased temperatures. In the Sahara Desert, there is support in many climate-model predictions for increased rainfall in the southern and southeastern areas (including the Sahel), but strong drying in the northern and western areas. Some models, however, suggest a strong drying throughout the region.
The differences between varioius models’ predictions for the Sahara demonstrate the complexity of forcing factors in the region, as well as the possible influence of feedbacks between land-surface conditions and the atmosphere. Such feedbacks could affect rainfall total, effectiveness, and spatial distribution. Most of the interior of southern Africa is also predicted to become drier, leading to the mobilization of sand dunes in the Kalahari Desert, as well as severe impacts on surface and groundwater resources.
In the southwestern United States, higher temperatures are predicted to increase the severity of droughts. Some models indicate that the region may already be in transition to a new, more arid state as a result of anthropogenically influenced climate change. The economies of many desert regions (including Atacama, the American Southwest, Iran, western China, and southwest Asia) depend on runoff derived from winter snow in mountain areas for domestic use and irrigated agriculture. Higher temperatures are already reducing the amount of snowpack and changing the timing and duration of spring runoff. More precipitation is falling as rain, leading to less natural storage and an increased risk of flooding. Such changes, if continued into the future, will require costly upgrades of water management systems and possibly a reduction in available water supply.
Many desert areas experienced significant increases in temperature and reductions in rainfall during the 1990s and early twenty-first century. During that time period, droughts occurred in the Colorado River Basin, Australia, Southern Africa, Iraq, and Afghanistan. Sand dunes occupy up to one-third of the area of many desert regions. Dune mobility is a function of the ratio between wind strength and effective rainfall and is measured by the dune mobility index. Increased temperatures, accompanied by decreased rainfall, are predicted to lead to remobilization of vegetated sand dunes in the Kalahari and drier areas of the Australian desert.
The effects of climate change on vegetation patterns in desert regions is difficult to separate from disturbance. Increased levels of atmospheric may increase plant productivity in arid regions. Higher CO2 levels may also favor invasive exotic species such as cheat grass, with possible effects on fire regimes in the Great Basin Desert. Models that incorporate CO2 fertilization of vegetation indicate a reduction in desert areas in the next century, introducing an additional level of uncertainty about the future of desert ecosystems.
During the 2020s, the advancement of global climate change caused significant problems in many desert communities. One of the most striking problems faced by these communities was a significant increase in the strength and frequency of sand and dust storms. To help raise awareness of this issue, in 2023, the United Nations named July 12 the first International Day of Combating Sand and Dust Storms.
Context
The great natural variability of climatic conditions, especially the distribution of rainfall in space and time, presents challenges for the prediction of the response of desert regions to future climate change. However, the experience of recent drought episodes indicates that the natural and human systems of deserts and desert margin areas are highly susceptible to soil moisture deficits. Climate change is expected to decrease water availability in all desert regions, through increased temperatures, changes in the amount of precipitation, or a combination of both. The result will be increased pressure on existing water resources for human and ecosystem use, possibly leading to higher levels of conflict over scarce resources.
Key Concepts
- drought: an extended period of months or years during which a region experiences a deficit in its water supply, mainly as a result of low rainfall
- dune mobility index: a measure of potential sand mobility as a function of the ratio between the annual percentage of the time the wind is above the sand transport threshold and the effective annual rainfall
- subtropical anticyclonic belts: a series of high-pressure belts situated at latitudes 30° north and south of the equator
Bibliography
"As Climate Changes, Sand Storms Wreak Havoc on Desert Communities." UN, 11 July 2023, www.unep.org/news-and-stories/story/climate-changes-sand-storms-wreak-havoc-desert-communities. Accessed 21 Dec. 2024.
Ezcurra, E., ed. Global Deserts Outlook. Nairobi, Kenya: United Nations Environment Programme, 2006.
Goudie, A. S. Great Warm Deserts of the World: Landscapes and Evolution. New York: Oxford University Press, 2002.