Putting drought in the spotlight

Of all the natural disasters, droughts strike right at the heart of life itself – no human, animal or plant can survive without water.

Yet their frequency, severity and duration are set to grow without radical action to reduce greenhouse gas emissions, writes Toby Ault from Cornell University, US, as part of a special issue in the journal Science dedicated to new insights on droughts.

The Earth isn’t new to megadroughts, Ault notes; throughout history they have brought powerful civilisations to their knees, including the Khmer and Mayan Empires and the Yuan Dynasty of China. 

But he warns that “[d]roughts of the future may eclipse those of past centuries”. 

Even low levels of warming could magnify their impact – especially in vulnerable regions such as the Caribbean, Central America, Brazil, western Europe, central Africa, South-East Asia and Australia.

And they can seemingly appear out of the blue; “like a disease, a drought begins before it presents any symptoms”, Ault writes.

In his review, he covers the analytical tools – including the “Internet of Things” – needed to understand droughts and their causes to help water resource managers and scientists in drought-prone areas further investigate and better understand them.

Cutting through the technicalities, he sums it up with one simple message.

“If you are a water resource manager and you remember just one thing from this review, it should be this: Cutting CO2 emissions reduces drought risk.”

Reducing warming by even half a degree Celsiusmakes a difference, he adds, emphasising that droughts will be more severe if global temperatures reach two degrees than if we achieve the 1.5-degree target.

In another paper, Megan Mullin, from Duke University in Durham, US, highlights the problems faced by vulnerable communities whose drinking water security is threatened by droughts, which could “push them to the brink of their water supplies”.

She explores the challenges of managing drinking water during droughts and the importance of tackling community water systems – both quality and quantity of drinking water – and related political constraints to address these disparities throughout the US.

Trees and forests are another major casualty of a drying planet, write Tim Brodribb from the University of Tasmania, Australia, and co-authors from Australia, the US and France.

Reviewing evidence from the last five years, they find that forest mortality is increasing, with grave ecological, atmospheric and financial consequences.

“Early suggestions that higher CO2 may benefit trees seems to be largely incorrect,” Brodribb says, “with the bulk of evidence indicating negative effects of increased temperatures.”

Like corals, trees are long-lived organisms, with intricately developed matrices to carry water over long distances from the roots to the leaves, prompting the researchers to investigate their vulnerability to climate change. 

“The slow construction of these carbon-dense, woody skeletons leads to a slow generation time, leaving trees and forests highly susceptible to rapid changes in climate,” they write.

The combined impact of warmer temperatures and water stress damage the tree’s vascular system, leading to high risk of death. 

This has hit Australian forests particularly hard, Brodribb says.

“Massive forest mortality in the hottest/driest year on record in Australia (2019) looks like it will greatly eclipse the impacts of the well-publicised fires.”

Clearly, all authors are pointing to the critical need to address climate change. Ault invites readers to transport themselves to a drought 15 years in the future.

“It is exceptionally hot, aquifers are depleted, and there are frequent blackouts because reservoir levels are so low at the hydroelectric power plant.

“What would you ask us – the people alive today – to do now to ensure that you are resilient in the face of drought in a changing climate?”