We May Have Crossed the Dryland Self-Expansion Tipping Point

The growing threat of self-propagating drylands and its implications for ecosystems and humans

When I was a little kid, I remember getting into the car and asking where we were going. We were visiting the Sau Reservoir (Pantà de Sau) in Catalonia (Iberian Peninsula). So was everyone. The waters were so low that you could see the old bell tower of the Church of Sant Romà for the first time in many years. We thought we’d never get the opportunity again.

Built in 1963 and with a capacity of 151.3 hm³, the Sau Reservoir covered the former town of Sant Romà de Sau, forever entombed in its watery depths. Or so we thought.

But this year, 2024, reached a new milestone. The water in the reservoir was not onyl low enough again to see the bell tower. But this time, people could visit the whole church on a dry sandy bed, meters away from any body of water. This blew my mind.

It has actually been this low for long enough to place a safety sign on its walls.

As you can imagine, the fact that rainfall is low enough to dry a whole reservoir means that ecosystems around are also suffering the consequences of sudden low precipitation. In fact, the expansion of the world’s drylands, areas characterized by low precipitation and high atmospheric water demand, is a growing concern in the context of climate change.

While it has long been recognized that global warming contributes to the spread of deserts, shrublands, and other dry regions, new research reveals a surprising event: drylands are accelerating their own expansion. As you can imagine, this finding has significant implications for ecosystems, agriculture, and human livelihoods in many parts of the world.

A study published in Science on August 29, 2024, led by researchers from Ghent University in collaboration with institutions like the University of Bristol and ETH Zurich, explains how existing drylands are actively contributing to the aridification of neighboring humid regions (a sort of conversion). This process, termed “dryland self-expansion,” means that as drylands grow, they create conditions that further their own spread into new territories.

But why is this happening? To understand how drylands might be driving their own expansion, the researchers employed a unique method of tracking atmospheric conditions over these regions. They used an observation-based Lagrangian atmospheric transport model to follow the air as it moved over drylands over a 38-year period (from 1981 to 2018).

This model allowed them to analyze how changes in heat and moisture in these regions influenced the climate of downwind areas, particularly focusing on how drylands might reduce precipitation and increase atmospheric water demand in neighboring regions.

The study found that about 5.2 million square kilometers of previously humid land transitioned into dryland over the study period, with dryland self-expansion accounting for more than 40% of this change.

In a nutshell, drylands are not just passively spreading due to external factors like global warming — they are actively creating conditions that push neighboring humid regions into aridity.

The self-expansion is driven by a feedback loop where drying soils in existing drylands release less moisture and more heat into the atmosphere. This warmer, drier air then moves downwind, reducing rainfall and increasing evaporation in adjacent regions.

Over time, this process transforms these neighboring areas into drylands as well. “Out of the approximately 5.2 million square kilometers of humid land that transitioned into dryland over the past four decades, more than 40% of the change was due to dryland self-expansion,” said Dr. Akash Koppa, the study’s lead author.

As drylands continue to expand, they threaten to disrupt ecosystems, agriculture, and human settlements worldwide. Regions such as Australia and parts of Eurasia have already seen significant impacts, with dryland self-expansion identified as the primary driver of aridification in these areas.

Thus, the study underscores the importance of addressing climate change not just on a global scale but also with targeted strategies to manage and mitigate the spread of drylands.

On the other hand, have you ever heard of the Amazon Tipping Point? It is a theory that predicts that, given enough deforestation, the Amazon may cross a threshold beyond which it will no longer be able to create its own precipitation as it is currently doing.

According to the study’s results, a similar process is already well underway worldwide. That’s not something we wanted to hear…

This research also highlights the vulnerability of certain regions to future dryland expansion. As the world continues to warm, the self-propagation of drylands could accelerate, posing even greater risks to biodiversity, food security, and socio-economic stability.

“As we continue to move towards a warmer and potentially drier future, the phenomenon of dryland self-propagation could accelerate, posing significant risks to human livelihoods, ecosystems, and socio-economic stability globally,” Dr. Koppa added.

The study’s findings emphasize the urgent need for climate change mitigation and sustainable land management practices. For example, In West Africa’s Sahel, USAID and the World Food Programme implemented half-moon ponds, a low-cost rainwater retention technique, to combat desertification and improve soil health. Satellite imagery analysis using NDVI showed a 50% increase in vegetation at the intervention sites, demonstrating the effectiveness of this approach in restoring degraded landscapes.

See the video below for a comprehensive explanation of how the process works. It looks like magic, but it’s just science… and community efforts!

All in all, this shows that if local communities, policymakers, and scientists understand the mechanisms driving dryland expansion, they can develop better strategies to slow this process and protect vulnerable regions. That’s why I’m so passionate about scientifically driven policy decision-making.

Beyond that, the researchers also call for coordinated conservation efforts in existing drylands to prevent further aridification and preserve these ecosystems’ delicate balance.

Understanding that drylands are driving their own expansion adds a new dimension to the challenges of climate change. By acknowledging and addressing this self-reinforcing process, we can take steps to mitigate its impact and safeguard the environments and communities at risk. This is not just a future tipping point; we seem to have tipped the balance already.