Millions at risk as drylands degrade, finds study

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Serengeti National Park in northern Tanzania represents a typical semi-arid, drySerengeti National Park in northern Tanzania represents a typical semi-arid, dryland ecosystem. (Lucy Witter)

Drylands are experiencing increasingly levels of degradation and desertification, changes that could put already vulnerable populations at greater risk.

A research team, including Natasha MacBean , conducted an examination of dryland productivity and its important role in global carbon and water cycling, to understand the impact of climate change and human activity on future dryland ecosystem functioning. Their paper, Dryland productivity under a changing climate, was published in Nature Climate Change .

Natasha MacBean

Drylands - those regions where precipitation is substantially smaller than atmospheric water demand - are the largest biome on earth, covering around 40 per cent of the world’s terrestrial surface. Drylands currently host more than 2 billion people, the vast majority of which live in developing countries. These regions are often more agriculturally productive than tropics or boreal forests and have acted as breadbaskets for millennia. Ongoing climate and environmental change threaten the viability of drylands and the populations that depend on them.

"Drylands are experiencing degradation and desertification from more intense droughts, changes in the frequency and intensity of rainfall, and intensive land management leading to loss of vegetation and soil," said MacBean, an assistant professor cross-appointed in the departments of Geography and Environment and Biology.

Data from the flux tower site at Santa Rita Experimental Range in southern Arizona was used to test and develop models for this study. (Natasha MacBean)

Complex factors are at play, with some, such as increased carbon dioxide levels encouraging woodland encroachment, and others, such as increased agricultural activity and deforestation leading to the expansion of drylands.

"Expected increases in water shortage and loss of vegetation with climate and environmental change intensifies potential threats to food, water, and livestock production," MacBean said. "Water shortages and declines in dryland plant productivity are already evident, putting some of the most vulnerable people on the planet at even greater risk."

These areas play key roles in earth system functioning, said MacBean, as hotspots of land-atmosphere interactions. Through varying levels of soil moisture and vegetation, drylands can impact local and regional precipitation. They are also thought to have an important role in the carbon cycle and the long-term capacity of the land to store carbon.

"Understanding dryland dynamics is essential to predict future climate trajectories," the authors state in the paper’s abstract.

MacBean is working to improve modelling of dryland ecosystem processes to enable better predictions of the impact of climate and environmental change on drylands.

"Understanding global carbon cycling and the feedback to climate is crucial for estimating how much of our carbon emissions will be stored on land versus how much will remain in the atmosphere (or in the ocean), thus exacerbating global warming," she said.

The research team highlights the importance of further data collection focused on dryland health. They also recommend planning for more sustainable dryland agriculture and land management practices.