Last updated January 31, 2018

Increased Drying of Soils

On land, global warming causes the soil to dry out, a process made worse by other climate signals such as permafrost thaw and evapotranspiration, and as rainfall is concentrated in heavy rainfall events with greater runoff. ​Soil can also dry out due to changes in large-scale circulation, such as the expansion of the Hadley Cell. As the Hadley Cell expands, dry air flowing from the tropics falls in the subtropics creating regions that are more arid. As aridity increases, dry land degrades and loses its water, vegetation and wildlife.

Global trends

Global warming is changing the pattern of wet and dry areas around the world. Scientists have broadly observed, and continue to expect, that climate change leads to dry regions getting drier, and wet regions wetter.

From 1979 to 2013, a study analyzing soil moisture from satellite data found that 30 percent of global land experienced robust moisture trends, with 22.16 percent becoming drier, and 7.14 percent becoming wetter.[1]

Another study analyzing annual mean soil moisture trends from 1948 to 2010 identified significant trends for 40.6 percent of the global area, with 60.2 percent of this area experiencing drier conditions, and 39.8 percent wetter.[2] The most prominent drying trends occurred in northern Africa, East Asia, eastern Australia, and southern Europe, whereas subtle increases in soil moisture were observed for the central US, South America, and western Australia.

By 2100, models project that many regions—including, the Mediterranean, Southwest US and southern Africa—are likely to get drier should greenhouse gas emissions continue unabated.[3]

Hadley Cell Expansion

Model projections indicate that the Hadley Circulation will shift its downward branch poleward in both the Northern and Southern Hemispheres, causing drying as a result.[3]

Scientists have already observed a poleward shift of the southern Hadley Cell.[3]