It is important to understand that most of the extreme climate change in Earth’s history occurred before humans existed. That being said, the rapid release of carbon dioxide into the atmosphere from human activity is currently causing a global warming event. The seemingly slight increase in the average annual temperatures in the Southwest over the past 25 years has been accompanied by more frequent heat waves, shorter winters, and an increased likelihood of drought and wildfires.

Although wildfires can occur during any season, summer fires are the most common, since increased dryness contributes to fire risk. Today these most often start due to human activities, such as a poorly extinguished campfire, but they can also occur by natural ignition from lightning. Hundreds of square kilometers (miles) of forest have been lost to wildfires despite our best efforts to prevent, control, and extinguish them. Rural towns and summer homes, along with the people who inhabit them, can be suddenly caught in the blaze. Not only do these fires spread quickly, but human attempts to extinguish the blaze are hindered by the lack of available water to fight the fire. The Wallow Fire, which raged from May to July 2011, was the largest fire in Arizona’s history; it consumed 2180 square kilometers (840 square miles) of land, destroyed 17 structures, and caused the evacuation of over 6000 people. In 2012, one of the Southwest’s worst wildfire years, 1041 fires burned across Colorado, destroying 90,875 hectares (224,559 acres) of land, while over 1000 fires in Utah scorched more than 171,000 hectares (422,000 acres). And fires don’t have to be large to be destructive—the most destructive fire in Colorado history, 2013’s Black Forest Fire, burned only 5780 hectares (14,280 acres) but destroyed 511 homes and led to two fatalities (Figure 9.34).

Figure 9.34: The remains of a home destroyed by Colorado’s Black Forest Fire on June 12, 2013.

Water supply is also a critical issue for the Southwestern states. Here, most water is obtained from precipitation, snowmelt, and runoff, which will dramatically decrease in quantity as temperature and aridity rise. In addition, parts of Colorado and New Mexico obtain agricultural and drinking water from the Ogalalla aquifer, an underground layer of water-bearing permeable rock. Part of the High Plains aquifer system, this underground reservoir supplies vast quantities of groundwater to the Great Plains. As drought intensifies and temperature rises, the amount of water drawn from the aquifer (especially for agricultural irrigation) has increased, while the rate at which the aquifer recharges has decreased. The aquifer’s average water level has dropped by about 4 meters (13 feet) since 1950, and in some areas of heavy use, the decrease is as high as 76 meters (250 feet) (Figure 9.35). However, the aquifer only replenishes at a rate no greater than 150 millimeters (6 inches) per year. Some estimates indicate that at its current rate of use, the entire Ogalalla aquifer could be depleted by as early as 2028, threatening human lives, our food supply, and the entire Great Plains ecosystem.

Figure 9.35: Water level change in the Ogalalla aquifer between 1950 and 2013.

In rural desert and semi-desert areas that are not served by well-planned regional or municipal systems, most people are dependent upon streams and wells. Streams often run dry, especially in the summer. The water table (the level of underground water) then migrates deeper, forcing people to extend wells deeper into the ground. Unfortunately, this is only a temporary solution.

In most of these areas, water is being withdrawn much more quickly than it is naturally replenished. Another hazard arising from excessive pumping of groundwater in the Southwest is land subsidence and subsidence-related earth fissures. In sum, lack of water reserves can lead to a cycle of economic disasters as well as the displacement of populations and businesses. The preservation and storing of water in large aquifers (water banking) for future use is an important technique to help adapt to drought.

Increasing temperatures also allow certain pests, such as ticks and mosquitoes, to live longer, thereby increasing the risk of contracting the diseases they carry. In addition, organisms that damage ecosystems, such as the bark beetle, are better able to survive warmer winters, thrive, and multiply. In recent decades, bark beetles are estimated to have affected more than twice the forest area burnt by wildfires in New Mexico and Arizona.

Another concern regarding hazards exacerbated by climate change in the Southwest is whether or not there has been or will be an increase in the number or severity of storms, such as hurricanes and tornados. According to NASA, the present data is inconclusive in terms of whether hurricanes are already more severe, but there is a greater than 66% chance that global warming will cause more intense hurricanes in the 21st century. Since climate is a measure of weather averaged over decades, it might take many years to determine that a change has occurred with respect to these types of storms. Scientists are certain that the conditions necessary to form such storms are becoming more favorable due to global warming. The Union of Concerned Scientists has created an infographic that demonstrates the relative strength of the evidence that various hazards are increasing as a result of climate change (Figure 9.36).

Figure 9.36: The strength of evidence supporting an increase in different types of extreme weather events caused by climate change.