The Southwest is currently enduring its driest 22-year period in 1,200 years
In short: The current megadrought in the Southwestern United States and Northern Mexico is not just a modern anomaly. While human-caused warming is intensifying the crisis, the region has a long history of extreme aridity that predates the industrial age by centuries.
A 2022 UCLA-led study, published in Nature Climate Change, used tree-ring patterns to reconstruct soil moisture levels across the Southwest. The research revealed that the megadrought spanning 2000 to 2021 is the driest 22-year period in the region since at least 800 CE. This period has exceeded the severity of a late-1500s megadrought, which was previously considered the driest such event in the 1,200-year record. The study area covers a vast expanse from southern Montana to northern Mexico. Researchers identified forty distinct drought events lasting at least 19 years within this timeframe. These historical records show that megadroughts occurred repeatedly between the years 800 and 1600.
The study highlights a complex interplay between natural cycles and human impact. While the region experienced dramatic shifts in water availability long before the 20th century, human-caused climate change is responsible for approximately 42% of the soil moisture deficit since 2000. Specifically, rising temperatures—which were 0.91 degrees Celsius higher from 2000 to 2021 than the 1950–1999 average—are accelerating evaporation, drying out vegetation and soil more rapidly than natural variability alone would dictate. The atmosphere's thirstiness, measured as surface air vapor pressure deficit, has risen rapidly. Human-caused global warming explains 68% of this specific increase. This process significantly drives the current rise in western wildfires.
Looking forward, the outlook remains challenging. Research indicates that extreme megadroughts are now a heightened threat for the Southwest, regardless of whether humans stop releasing greenhouse gases. However, mitigation efforts can still provide some relief. Data for Texas suggests that the final 50 years of this century could be more parched than any period in the past millennium, which might result in a major drop in water storage. Projections for the latter half of the 21st century suggest even more arid conditions than any of the last 1,000 years. These models are robust in predicting decreasing reservoir supplies for both eastern and western Texas. Experts emphasize that multiple wet years would be required to remediate the current soil moisture deficit.
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Sources
- Summary by Intellect · source: Research Spotlight: Climate-Driven Megadrought | Drought.gov
- Also: Rapid intensification of the emerging southwestern North American megadrought in 2020–2021 | Nature Climate Change
- Also: Megadrought in southwestern North America is region’s driest in at least 1,200 years | UCLA
- Also: Southwestern North American megadrought
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