20-year megadrought is worst on record
Scientists had already considered the period from 2000 to 2021 to be one of serious drought for the American Southwest, but the summer of 2021 was so dry that it caused the period to become the worst in recorded history. The drought was largely due to human-caused climate change and exacerbated wildfires in the area.
The level of rainfall required to avoid drought varies from region to region. In his video series The Science of Extreme Weather, Professor Eric R. Snodgrass, Director of Undergraduate Studies for the Department of Atmospheric Sciences at the University of Illinois at Urbana–Champaign, describes the types of drought.
“Plants are an excellent indicator of drought—their drought stress signals are easily recognized as changes in [their] physical appearance and color,” Professor Snodgrass said. “Just a few days without adequate water and the plant will show signs of distress. Agricultural drought is a reduction in topsoil moisture, and is often the first type of drought to set in for a region, and can be relatively short in duration.”
Next up is “meteorological drought.” Meteorological drought is defined as an extended period of below normal precipitation. Precipitation levels are monitored closely by Doppler radar, rain gauges, and even satellites, all of which are useful tools for detecting considerable dry spells.
“If the groundwater levels drop or stream and river flow are reduced, then a region is said to have experienced hydrological drought,” Professor Snodgrass said. “This kind of drought is often categorized as long-term drought, because it often lasts several months, and [it] also takes a longer time to recover from.”
In 2006, Atlanta experienced all three kinds. Professor Snodgrass said that a lack of rain combined with intense heat dried out the topsoil, resulting in agricultural drought and meteorological drought. With both affecting the local climate, they eventually produced evidence of hydrological drought when Lake Lanier and Lake Altoona water levels dropped below “full pool,” negatively affecting cotton and peanut crops in the area.
“The conditions of these three types of drought led to the fourth and worst form of drought—socioeconomic drought,” Professor Snodgrass said. “A socioeconomic drought occurs when water supply is reduced for human consumption. Lake and reservoir levels continued to fall, and water restrictions were instituted for Atlanta and the surrounding cities.”
Water levels in Lake Lanier, he said, hovered at just 20 feet above crisis level. Residents prepared for the worst as they watched their lakes dry up. That winter, enough rain fell to refill the reservoirs, but the meteorological event was nothing short of a close call that left a major metropolitan area on edge.
The drought currently affecting the American Southwest is considered a “megadrought,” which is generally considered to be a severe drought lasting up to several decades.
Edited by Angela Shoemaker, The Great Courses Daily
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