Droughts are becoming more severe and widespread across the globe. But it's not just changing rainfall patterns that are to blame. The atmosphere is also getting thirstier.
In a new study published in Nature, my colleagues and I show that this rising "atmospheric thirst" – also known as atmospheric evaporative demand (AED) – is responsible for about 40% of the increase in drought severity over the last four decades (1981-2022).
Imagine rainfall as income and AED as spending. Even if your income (rainfall) stays the same, your balance goes into deficit if your spending (AED) increases. That's exactly what's happening with drought: the atmosphere is demanding more water than the land can afford to lose.
As the planet warms, this demand grows – drawing more moisture from soils, rivers, lakes, and even plants. With this growing thirst, droughts are getting more severe even where rain hasn't significantly declined.
The process of AED describes how much water the atmosphere wants from the surface. The hotter, sunnier, windier and drier the air is, the more water it requires – even if there isn't less rain.
So even in places where rainfall hasn't changed much, we're still seeing worsening droughts. This thirstier atmosphere is drying things out faster and more intensely and introducing more stress when this water is not available.
Our new analysis reveals that AED doesn't just make existing droughts worse – it expands the areas affected by drought. From 2018 to 2022, the global land area experiencing drought rose by 74%, and 58% of that expansion was due to increased AED.
Our study highlights that the year 2022 stood out as the most drought-stricken year in over four decades. More than 30% of the world's land experienced moderate to extreme drought conditions. In both Europe and east Africa, the drought was especially severe in 2022 – this was driven largely by a sharp increase in AED, which intensified drying even where rainfall hadn't dropped significantly.
In Europe alone, widespread drying had major consequences: reduced river flows hindered hydropower generation, crop yields suffered due to water stress, plus many cities faced water shortages. This put unprecedented pressure on water supply, agriculture and energy sectors, threatening livelihoods and economic stability.
My team's new research brings clarity to the dynamics of drought. We used high-quality global climate data, including temperature, wind speed, humidity and solar radiation – these are the key meteorological variables that influence how much water the atmosphere can draw from the land and vegetation. The team combined all these ingredients to measure AED – essentially, how "thirsty" the air is.
Then, using a widely recognised drought index that includes both rainfall and this atmospheric thirst, we could track when, where and why droughts are getting more severe. With this metric, we can calculate how much of that worsening is due to the atmosphere's growing thirst.
The future implications of this increasing atmospheric thirst are huge, especially for regions already vulnerable to drought such as western and eastern Africa, western and south Australia, and the southwestern US where AED was responsible for more than 60% of drought severity over the past two decades.
Without factoring in AED during drought monitoring and planning, governments and communities may underestimate the true risk they face. With global temperatures expected to rise further, we can expect even more frequent and severe droughts. We need to prepare. That involves understanding and planning for this growing atmospheric thirst.
Driving drought
Knowing what is causing droughts in each specific location enables smarter climate adaptation. AED must be a central part of how we monitor, model and plan for drought.
Identifying the specific drivers of drought is essential for tailoring effective ways to cope with drought. If droughts are mainly due to declining rainfall, then the focus should be on water storage and conservation. But if AED is the main driver – as it is in many places now – then strategies must address evaporative loss (i.e. the amount of water lost from the surface and plants to the atmosphere) and plant water stress. This might involve planting drought-resistant crops, constructing irrigation systems that use water more efficiently, improving soil health or restoring habitats to keep moisture in the land.
As our research shows, rising AED – driven by global warming – is intensifying drought severity even where rainfall hasn't declined. Ignoring it means underestimating risk.
Solomon Gebrechorkos, Reserach Fellow in Climate Change Attribution, University of Oxford
This article is republished from The Conversation under a Creative Commons license. Read the original article.