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The Alarming Reality of Dryland Self-Expansion in 2024

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Chapter 1: The Disappearance of Water in Catalonia

Reflecting on my childhood, I recall a trip to the Sau Reservoir in Catalonia, a visit shared by many others. The water level was so low that we could finally see the old bell tower of the Church of Sant Romà, a sight hidden for years. It was a surreal moment, with the reservoir, built in 1963 and holding a capacity of 151.3 hm³, once submerging the town of Sant Romà de Sau.

View of the Sau Reservoir revealing the Church of Sant Romà

However, in 2024, the situation became even more striking. Not only was the bell tower visible, but visitors could also walk on the formerly submerged sandy bed, now several meters away from the reservoir's water. This astonishing sight had remained low enough for long periods that a safety sign had to be posted on the church's walls.

The Church of Sant Romà now accessible due to low water levels

Such diminished rainfall, leading to a dry reservoir, has dire consequences for local ecosystems. The expansion of drylands, characterized by limited precipitation and high atmospheric water demand, is increasingly alarming within the context of climate change. While it's been known that global warming contributes to desertification, recent findings reveal that drylands are hastening their own spread. This revelation holds serious implications for ecosystems, agriculture, and human livelihoods worldwide.

A recent study published in Science on August 29, 2024, led by researchers from Ghent University alongside institutions like the University of Bristol and ETH Zurich, uncovers how existing drylands contribute to the aridification of adjacent humid areas. This phenomenon, termed "dryland self-expansion," suggests that as drylands increase, they create conditions that facilitate their own encroachment into new regions.

Global map showing existing and expanding drylands

But what drives this self-expansion? To unravel this, researchers used an observation-based Lagrangian atmospheric transport model to track air movement over drylands for 38 years (1981-2018). This methodology allowed them to examine how variations in heat and moisture impacted climate downwind, particularly regarding the reduction of precipitation and increased atmospheric water demand in neighboring areas.

The study revealed that approximately 5.2 million square kilometers of previously humid land transitioned into drylands during this period, with dryland self-expansion accounting for over 40% of this transition. In essence, drylands are not merely spreading due to external factors like global warming; they are actively creating the conditions necessary to extend their reach into surrounding humid territories.

Conceptual representation of dryland expansion processes

The self-expansion occurs through a feedback loop. Dry soils in existing drylands release less moisture and more heat into the atmosphere. This warmer, drier air travels downwind, leading to decreased rainfall and heightened evaporation in adjacent regions. Over time, these shifts transform neighboring areas into drylands as well. "Out of the roughly 5.2 million square kilometers of humid land that transitioned into dryland over the last four decades, more than 40% of the change was due to dryland self-expansion," stated Dr. Akash Koppa, the study's lead author.

As drylands continue to proliferate, they pose significant threats to ecosystems, agriculture, and human settlements globally. Regions like Australia and parts of Eurasia are already experiencing significant effects, with dryland self-expansion identified as a primary driver of aridification in those areas.

This video discusses how cascading climate tipping points are rapidly approaching as global temperatures surpass the critical 1.5°C threshold. The implications of these changes are profound and far-reaching.

Chapter 2: The Amazon Tipping Point and Global Implications

Have you heard about the Amazon Tipping Point? This theory suggests that extensive deforestation could push the Amazon beyond a threshold where it can no longer generate its own precipitation. Alarmingly, the study indicates that a similar process is already occurring globally, which is a sobering realization.

This research highlights the vulnerability of certain regions to future dryland expansion. As global temperatures rise, the self-propagation of drylands could quicken, posing increasing risks to biodiversity, food security, and socio-economic stability.

"As we advance towards a warmer and potentially drier future, the phenomenon of dryland self-propagation could escalate, threatening human livelihoods, ecosystems, and global socio-economic stability," Dr. Koppa noted.

The second video elaborates on how climate tipping points are inexorably approaching, emphasizing the urgency of addressing these challenges.

The findings of this study accentuate the critical need for climate change mitigation and sustainable land management practices. In West Africa's Sahel, initiatives such as half-moon ponds, a cost-effective rainwater retention technique, have been implemented by organizations like USAID and the World Food Programme to combat desertification and enhance soil health. Satellite imagery analysis using NDVI has shown a 50% increase in vegetation at intervention sites, illustrating the success of this method in revitalizing degraded landscapes.

In conclusion, if local communities, policymakers, and scientists grasp the mechanisms driving dryland expansion, they can devise better strategies to mitigate this process and protect vulnerable regions. This conviction fuels my passion for evidence-based policy decision-making.

Furthermore, the researchers advocate for coordinated conservation efforts in existing drylands to avert further aridification and maintain the delicate balance of these ecosystems. Recognizing that drylands are self-expanding adds a new layer of complexity to the challenges posed by climate change. By addressing and acknowledging this self-reinforcing process, we can implement measures to lessen its impact and safeguard the environments and communities at risk. This isn't just a potential tipping point; we may have already crossed that line.

Published in The New Climate. Stay updated on the latest in climate action.