Drying Of The American Southwest

Plate Tectonics

Last Updated on Mon, 16 Jan 2023

A drought is a prolonged lack of rainfall in a region that typically experiences a significant amount of precipitation. If a desert normally receives a small amount of rainfall, and it still is getting little rainfall, then it is not experiencing a drought. In contrast, a different area that normally receives more rainfall than the desert may be experiencing a drought if it normally receives significantly more rainfall than it is at present, even if it still experiences more rainfall than the desert. A drought-plagued area may become a desert if the drought is prolonged. Droughts are the most serious natural hazard in terms of their severity, area affected, loss of livelihood, social impact, and other long-term effects. Droughts can cause widespread famine, loss of vegetation, loss of life, and eventual death or mass migrations of entire populations.

Droughts may lead to the conversion of previously productive lands to desert. This process, called desertification, may occur if the land is stressed before or during the drought, typically from poor agricultural practices, overuse of ground and surface water resources, and overpopulation. Global climate undergoes several different variations that can cause belts of aridity to shift back and forth with time. The Sahel region of Africa has experienced some of the more severe droughts in recent times. The Middle East and parts of the desert southwest of the United States are overpopulated and the environment there is stressed. If major droughts occur in these regions, major famines could result and the land may be permanently converted to desert.

Much of the desert southwest region of the United States was settled in the past century following a century of historically high rainfall. Towns and cities grew, and the Bureau of Land Management diverted water from melting snows, rivers, and underground aquifers to meet the needs of growing cities. Some of the country’s largest and newest cities, including Phoenix, Tucson, Denver, Las Vegas, Los Angeles, San Diego, and Albuquerque, have grown out of the desert using water from the Colorado River system. Even though the temperatures can be high, the air is good, and many people have chosen to move to these regions to escape crowded, polluted, or allergen-rich cities and air elsewhere. The surge in population has been met with increases in the water diverted to these cities, and fountains, swimming pools, resorts, golf courses, and green lawns have sprung up all over. In general the life can be comfortable.

In the past decade the water supply seems to be diminishing. Lake Powell in Arizona has shrunk to half its capacity, and the Colorado River flow shrunk to a quarter of its typical rates. The Colorado River typically supplies 30 million people with water and irrigates 4 million acres of fertile farmland, producing billions of dollars worth of crops. The massive water work systems across seven states in the Southwest were all built using river-flow data for the Colorado River based on 20th-century flow records. Now studies of the ancient climate history in the region going back thousands of years indicate that the 20th century may have been one of the wettest on record for the region. The Hoover Dam, the California aqueduct, and cities across the region were all built during this high-flow stage of the Colorado River, and water budgets for the region were calculated assuming these flows would continue. Now precipitation is decreasing, and the historical records show that the region regularly experiences droughts where the flow decreases to 80 percent and even 50 percent of the

20th-century values used for building the civilization in the desert southwest. Now that more than 80 percent of the water from the river is used for human consumption, droughts of this magnitude have severe implications for any community, and the water wars of the southwest may eventually start again. Historical records show that past civilizations such as the Anasazi in the region disappeared at the end of the 13th century during a similar drought period, and similar trends are expected by climate modelers for the future in the region.

Climate-change models released by the National Ocean and Atmospheric Administration show that the flow of the Colorado River may decrease to half of its 20th-century values by the middle of this century, and that these lower flow values will persist into the foreseeable future. The region is already experiencing rapid changes, with wildfires burning huge tracts of vegetation and occasional storms initiating mud-flows and other desert processes. Climate models predict a likely descent of the region into dust bowl conditions, and these changes have already begun. The region saw many mega-droughts in medieval times and throughout history, and states of the region need to prepare for the likelihood of many years of water shortage and increasing drought conditions.

Continue reading here: Trade wind or hadley cell deserts

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