1000 years of climate records may hold key to dryland spread

More than 4,600 climate records spanning over a millennium will be used to investigate how humid regions become drylands, as part of a new study by scientists at the University of Reading.

Dr Akash Koppa, of the Department of Geography and Environmental Sciences, has been awarded €1.68 million from the European Research Council's Starting Grant scheme to lead the project, Land-atmosphere interactions as a mechanism of dryland formation (LAMDA).

LAMDA has three main goals: to find out how long-term drying of the atmosphere changes vegetation in a region; to determine how those changes drive the transformation of humid regions into drylands, both locally and further afield; and to assess how human activities speed up or slow down the process.

Dr Koppa said: “We know surprisingly little about why a humid region dries out permanently. The usual explanations, like changes in the Earth's orbit, happen over millions of years and can't account for what we're seeing today.

“Our idea is that vegetation itself is part of the mechanism. When plants come under water stress, die back and are replaced by drought-tolerant species, the land releases less moisture and more heat into the air. The atmosphere becomes drier both locally and in regions downwind, where rainfall depends in part on moisture carried from elsewhere.”

This project builds on research by Dr Koppa, published in Science in 2024, which showed that this process has driven existing drylands to expand into neighbouring humid regions over the last 40 years. LAMDA will investigate whether the same mechanism has also driven the formation of drylands over much longer timescales.

To do this, the team will build the first reconstruction of the global atmosphere over the past 1,150 years, combining climate modelling with more than 4,600 paleoclimate records from tree rings, ice cores, corals and sediments.

Researchers will then trace the paths of millions of air parcels through the reconstructed atmosphere, tracking the moisture and heat they carry from their source regions to where that moisture ultimately falls as rain. This will allow them to identify where vegetation changes are contributing to drying elsewhere, even across large distances.

Water scarcity

Drylands already cover about 45% of the Earth's land surface, and in the last four decades around 5 million square kilometres of humid land – an area roughly half the size of Europe – has turned to dryland. Around 4 billion people already face water scarcity as a result, and climate change is expected to accelerate the expansion of drylands in the coming decades.

The project's final output will be a set of global maps showing which regions are most vulnerable to becoming drylands because of specific human activities, including deforestation, afforestation, irrigation and rising carbon dioxide levels – even where those activities take place far upwind.

The five-year project runs from January 2027 to December 2031.

From Fossils to Futures: Find out more about how Reading researchers are using deep history to shape the future of our planet.

Photo by Bernard Hermant on Unsplash