If you look at an image of Earth from space, you can easily spot several vast brown tracts. The Gobi and Taklamakan in Asia, the Sahara and Namib in Africa, the Sonaran Desert in North America, along with many others, comprise these areas of limited vegetation, little to no rainfall, and often high temperatures. The Sahara alone covers over 9 million square kilometers, making it as large as the continent of Europe or the United States.
If you could go back in time, 50, 100 years ago, though, many of these deserts were smaller. Climate change alone cannot explain why. Desertification claims 6 million hectares a year, an area nearly the size of West Virginia. After 7 years, that’s an area the size of California.
There are several causes of desertification, all of human origin. These include overdrawing on subsurface water, the diversion of surface water for human and industrial use, and the greatest amount of damage is caused by over-grazing and other agricultural purposes.
Much of the sub-surface water in arid and desert regions is what’s often referred to as fossil water. These aquifers, once drained, do not get replenished on any sort of meaningful time scale. Essentially, once used, they are done, and the water they held no longer available for the region’s plant and animal use. Without the water, plants perish, and are no longer able to retain the soil. The deserts spread.
Surface water is also diverted for human use, whether for industrial uses or to water lush grass lawns that really shouldn’t be in the middle of a desert. Even water used in irrigation falls into this category. The water will typically evaporate before runoff can carry it back to surface water sources, and so it, too, is lost to the region. And the desert spreads.
Africa has over 600 million people, and nearly that many head of livestock. As the population increases, more livestock are bred to support the people. These societies are still very much agrarian, and even nomadic, societies. They rely on their herds to support them, and provide milk, meat and skins. Unfortunately, these herds are the main cause of the increasing area of the Sahara. The large herds, mainly goats and sheep, can graze available forage right down to the ground, while their hooves compact the loose ground, preventing further growth. The ground cover dies. The desert spreads.
In the uplands of Madagascar, there is a desert that covers nearly 10% of the entire country. This desert is relatively new, and is the result of slash-and-burn agricultural methods. The soils of many forest regions is fairly poor, and when the ground cover has been burned away, the soil is quickly exhausted. The farmers move on to the next plot of land, to burn again. In the abandoned fields, there is nothing left to hold the soil, and the winds start to blow. The desert grows.
In some of these cases, the people involved have little or no choice in the matter. They have to survive, and their animals, or their crops, are the only way they have to do so, they have no options. In the developed world, however, there are options, and no excuses.
There is no quick and easy fix for desertification. Some areas have taken to building sand fences of living trees, in an attempt to stop the land from blowing away. In the developed world, the means exist to more efficiently use the water resources available, and to protect the land, should the will be there. In the developing world, though, as long as most people are subsistence farmers, the problem will continue. Better land management practices would help, though, and would go a long way to checking the spread of the world’s deserts.