Meteorologists are tracking hurricanes over oceans, forecasting where and when land subsidence may occur so that residents can prepare for disaster before it strikes. What if they could do the same thing in a drought?

Stanford scientists have now shown that it may be possible in some cases – researchers have identified a new type of “landfall drought” that can be expected before it affects people and ecosystems on Earth. They found that these droughts, which form over the ocean and then migrate to land, can cause larger and drier conditions than droughts that occur only over land. Of all the droughts that affected land areas around the world from 1981 to 2018, one in six were caused by landfall, according to the study published on September 21 Water Resources Research.

Lead author Julio Herrera-Estrada said: “We usually don’t think about droughts over the ocean – it might seem counterintuitive. But just like on land, there can be times when large areas of the ocean get less rain than normal.” Research Associate with Water in the West who conducted the study for the study while he was a postdoctoral researcher at Stanford University’s School of Earth, Energy and Environmental Sciences (Stanford Earth). “Hopefully, the discovery that some droughts are starting abroad will spur conversations about the benefits of monitoring and forecasting droughts outside of continents.”

Droughts can harm or destroy crops, as well as affect water supplies, electricity generation, trade, and ecosystem health. Historically, droughts displaced millions of people and cost billions of dollars. However, the climate processes that lead to droughts are not fully understood, making accurate predictions difficult.

In order to identify large-scale droughts that have originated over the ocean, researchers have used an object-tracking algorithm to identify and track groups of moisture deficits around the world, decades ago. They found that dry spells that land on land have grown at a rate three times as fast as the drought on land only, and usually take several months to reach the continent.

“Not all droughts that cause harm to humans and ecosystems will be droughts that land on land,” said lead author and climate scientist Noah Diefenbo, professor at the Kara J Foundation at Stanford Earth. “But there is something about droughts that start over the ocean that make them more likely to turn into large, intense events.”

The researchers analyzed the physical processes of drought in western North America, where high frequency occurs. They found that droughts reaching land in the region were associated with specific atmospheric pressure patterns that reduce humidity, similar to the “Ridiculious Resilient Ridge” pattern that was one of the main causes of the 2012-2017 California drought.

The authors state that further analyzes may reveal similar or new explanations for the droughts that have ravaged land that they have identified in other regions of the world, including Chile, Argentina, New Zealand and eastern Australia.

“Our paper shows that droughts are a global phenomenon that affects every continent,” said Herrera Estrada. “There will definitely be a need for other studies to focus more on the relevant physical processes for each region separately.”

According to the researchers, given the significant human and economic impacts of severe droughts, the predictability of drought may require further investigation.

“This is an important finding because droughts that land on land are statistically more likely to be larger and more severe than droughts that do not reach land,” said Diefenbo, who is also a senior fellow at the Kimmelman family at the Stanford Woods Institute for the Environment. “Since it usually takes a number of months to migrate to land, there is a possibility that tracking the lack of moisture over the ocean provides an advance warning to help protect against at least some severe droughts.”