Drought tolerance

Droughts are caused by prolonged periods in which there is little or no precipitation, leading to water shortages. Plant and animal species respond to drought stress in different ways, known as drought tolerance. Plants that have adapted to arid and semiarid climates are known as xerophytes and include cacti and succulents. Domesticated animals that survive best in drought conditions include camels, some types of cattle, and small herded animals such as sheep and goats.

Brief History

For centuries, Indigenous people around the world have pioneered methods to adapt to droughts. Indigenous communities have cultivated drought-resistant crops and raised animal breeds known to be more tolerant of drought. For instance, the Hmong in Vietnam developed crop varieties like hilly sticky rice that are more resistant to droughts. Indigenous people have also developed ways to deal with the impacts of drought. Those native to the US Pacific Northwest, for example, grew zucchini plants that helped to prevent drought-related fires and used beaver dams to increase water storage during periods of drought. The Miriwoong in Australia burned native grasses in specific patterns to help prevent bushfires during the dry season.

Farmers, too, have long considered the best way to adapt to droughts. They have selected crops that can either continue to produce during a drought or will be able to reproduce or rebound after a drought is over. When these crops are planted with care, they can survive a drought and do not require additional irrigation.

Herding communities, known as pastoral nomads, have also adapted to droughts by domesticating and keeping herds of drought-tolerant animals such as camels, sheep, and goats. Because they are able to move their herds to new pastures, they are able to avoid drought conditions. Herders are often successful in drought-prone areas because they do not rely on planning and harvesting crops. Instead, the majority of their food comes from their herd animals in the form of meat and milk.

Farmers and herders have historically prepared for and survived droughts in arid regions, such as deserts and areas alongside deserts. In regions such as central Mongolia, winter droughts are common and occur when there is not enough snowfall. These winter droughts cause problems for herders because in the spring there is not enough snowmelt to water new grasses and their herd animals do not have enough to eat as a result. To cope with winter droughts, herders must move their herds to other regions of the country that have enough water. Farmers who are faced with the same situation must bring water from elsewhere. This process is known as irrigation.

Drought Tolerance Today

Agricultural researchers are working to determine the best ways for plants and animals to adapt to changing patterns of drought brought on by climate change. The United Nations estimates that by 2030 nearly half the world’s population will be living in areas facing serious water shortages. One of the regions expected to be affected by these changes is sub-Saharan Africa, where up to 250 million people may face conditions of water scarcity by 2030. To prepare for these demographic and climatic changes, agricultural researchers are developing drought-tolerant crops that can adapt to and thrive in drought conditions. Much of this knowledge has been learned from studying Indigenous communities around the world and the methods they developed and have used for centuries to deal with drought.

For example, some researchers are exploring genetic engineering to create plant species that can grow and produce with lower levels of water. Such changes have been made to corn crops and have included breeding corn plants to have longer roots, which can reach water deeper underground. Other crops have been bred to have leaves that lose less water during photosynthesis. By developing and breeding drought-tolerant crops, scientists hope to secure the world’s food supply and reduce the demand placed on water supplies by agricultural irrigation. Critical to this effort is ensuring these new crops are still affordable to farmers and consumers in developing countries.

Other researchers have been advocating for a change in the ways in which crops are planted. These researchers suggest that farmers should replace crops that require a lot of water for those that can thrive on less or grow alongside other crops. Using a method known as "complementary crop management," farmers are encouraged to grow several crops next to one another in an attempt to minimize the loss of soil and best use the available water in one area rather than having to irrigate large spaces. Furthermore, by growing plants closer together, the soil is more likely to remain shaded during the day, resulting in less water lost to evaporation.

Herders have also been making changes. In Texas, some cattle ranchers are beginning to crossbreed their cattle breeds with those from India and sub-Saharan Africa. These new breeds of cattle have a different physiology, often weighing less and therefore requiring less water. Additionally, small cattle eat less, which means that less water is needed to grow the crops that are fed to cattle. These types of changes allow consumers to maintain meat-eating diets while lessening the impact of cattle herds on the supply of water and crop volatility caused by drought.

Policymakers have also entered these debates, working to regulate how much water farmers can access, how to promote the planting of drought-tolerant crops and how to resolve conflicts when multiple stakeholders demand to use the same water table. For example, in southern California, policymakers are encouraging homeowners and landscapers to plant native shrubs and grasses that are better adapted to the semiarid conditions there in order to minimize the need for homeowners to water their lawns. The term xeriscaping describes a landscaping method in which drought-tolerant plants, efficient methods of irrigation, and mulch are used to reduce evaporation and water use. Some homeowners have also opted to seed their lawns with grasses that have better drought resistance and summer dormancy capabilities than traditional bluegrass.

While many areas around the world are facing drought conditions, these scientific advances and practical changes are ensuring that crops are still alive and producing food. Without such advances, many crops would have succumbed to drought stress and significantly reduced their output or died. Climate scientists expect that droughts will continue to occur and may increase in frequency due to climate change. However, by developing and implementing drought-tolerant crops and herds, humans will be able to adapt to their changing environments.

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