Study: Earth's Drylands Could Cover 40% of Land by 2100

The world's driest places are getting drier, and the boundary between arid and habitable land is shifting. By the end of this century, drylands—regions where water scarcity is severe enough to limit plant growth and human settlement—could blanket more than 40 percent of Earth's land surface, according to new research published in Environmental Research Letters. That expansion would be equivalent to adding a territory the size of Algeria to the world's already parched zones.

Scientists from the Chinese Academy of Forestry and their collaborators used updated climate modeling to map where drylands exist today and where they will likely spread as temperatures rise. They defined drylands using a measure called the aridity index, which compares a region's rainfall to the amount of water plants and soil lose through evaporation and transpiration. Any area where that ratio falls below 0.65 qualifies as dryland. By this standard, drylands currently cover about 38.58 percent of Earth's land, excluding Antarctica. The four subtypes range from semi-arid zones, which make up 14.72 percent of terrestrial area, to hyper-arid deserts like those in Algeria, Libya, and Saudi Arabia, which account for 6.27 percent.

The projections for 2071 to 2100 show drylands expanding to between 39.31 and 40.28 percent of global land, depending on which greenhouse gas emissions scenario unfolds. The largest growth will occur in hyper-arid zones, the most extreme category. That upper estimate of 40.28 percent represents an increase of 2.37 million square kilometers—roughly equivalent to 30 percent of Australia's total land area. The consequences ripple outward: as dryland climatic conditions creep into regions that were once more humid, water scarcity intensifies, ecosystems degrade, and desertification accelerates, all of which threaten sustainable development and the livelihoods of people dependent on those landscapes.

One finding stands out as counterintuitive. Rising atmospheric carbon dioxide, the primary driver of climate change, may actually be slowing the expansion of drylands. When CO2 levels rise, the tiny pores on plant leaves called stomata partially close, reducing the amount of water plants lose through transpiration. This means less water escapes the soil, which affects how scientists calculate potential evapotranspiration—a key variable in the aridity index. Many previous studies failed to account for this CO2 effect, leading them to overestimate how much drier the world would become. The researchers incorporated this factor into their analysis using climate models from the sixth phase of the Coupled Model Intercomparison Project and historical meteorological data spanning 1960 to 2023.

Because of this adjustment, their projections are substantially lower than some earlier estimates. A decade ago, one study suggested drylands could cover as much as 56 percent of Earth's land by 2100. The new figures, while still alarming, offer a somewhat less catastrophic picture—though the distinction between 40 and 56 percent is small comfort when discussing the habitability of entire continents.

The geographic burden will not be evenly distributed. Australia, the world's driest inhabited continent, faces the most pronounced dryland expansion this century, followed by Brazil. Parts of Africa are also expected to experience widespread shifts toward more arid conditions. The researchers emphasize that updated assessments of dryland extent and future redistribution are essential for climate adaptation and sustainable development planning. Without such understanding, societies will struggle to prepare for the water scarcity, ecosystem collapse, and desertification that accompany the creeping expansion of the world's dry zones.