As a climate scientist, I’ve watched how climate change is making drought conditions increasingly worse — particularly in the western and central U.S. The last two years have been more than 2 degrees Fahrenheit (1.1 Celsius) warmer than normal in these regions. Large swaths of the Southwest have been even hotter, with temperatures more than 3 F (1.7 C) higher. Studies suggest the Southwest’s ongoing 20-year drought is the most severe in at least 1,200 years, based on how dry the soils are.
A hotter atmosphere sucks more moisture from the soil
A thristier atmosphere tends to extract more water out of the land. It exacerbates evaporative stress on the land, particularly when a region is experiencing below-normal precipitation. High evaporative stress can rapidly deplete soil moisture and lead to hotter temperatures, as the evaporative cooling effect is diminished. All this creates hydroclimatic stress for plants, causing restricted growth, drying and even death.
The thistier atmosphere is turning what would otherwise be near-normal or moderately dry conditions into droughts that are more severe or extreme. As the climate heats up further, the increasing atmospheric thirst will continue to intensify drought stress, with consequences for water availability, long-lasting and intense heat stress, and large-scale ecosystem transformation.
The changing nature of droughts is a concern even in parts of the U.S. that are expected to have a net increase in annual precipitation during the 21st century. In a hotter future, because of the high evaporative demand on the land, prolonged periods with weeks to months of below normal precipitation in these areas can lead to significant drought, even if the overall trend is for more precipitation.
Large parts of the northern Plains, for example, have seen precipitation increase by 10% or more in the last three decades. However, the region is not immune to severe drought conditions in a hotter climate.
Flash droughts are also emerging as a growing concern in the Northeast. In 2020, much of New England experienced an extreme hydrologic drought, with low stream flows and groundwater levels and widespread crop losses between May and September. Aided by very warm and dry atmospheric conditions, the drought developed very rapidly over that period from what had been above-normal wet conditions.
As humanity enters a hotter future, prolonged periods of weeks to months of below-normal precipitation are going to be of a greater concern almost everywhere.