Newly identified 'landfalling droughts' originate over ocean

Date:
September 24, 2020
Source:
Stanford University
Summary:
Researchers have identified a new type of 'landfalling drought'
that originates over the ocean before traveling onto land, and
which can cause larger, drier conditions than other droughts.



FULL STORY ========================================================================== Meteorologists track hurricanes over the oceans, forecasting where and
when landfall might occur so residents can prepare for disaster before
it strikes.

What if they could do the same thing for droughts?

========================================================================== Stanford scientists have now shown that may be possible in some instances
- - the researchers have identified a new kind of "landfalling drought"
that can potentially be predicted before it impacts people and ecosystems
on land. They found that these droughts, which form over the ocean and
then migrate landward, can cause larger and drier conditions than droughts
that occur solely over the land. Of all the droughts affecting land areas worldwide from 1981 to 2018, roughly one in six were landfalling droughts, according to the study published Sept. 21 in Water Resources Research.

"We normally don't think about droughts over the ocean -- it may even
sound counterintuitive. But just as over land, there can be times where
large regions in the ocean experience less rainfall than normal," said
lead author Julio Herrera-Estrada, a research collaborator with Water in
the West who conducted research for the study while he was a postdoctoral researcher at Stanford's School of Earth, Energy & Environmental
Sciences (Stanford Earth). "Finding that some droughts start offshore
will hopefully motivate conversations about the benefits of monitoring
and forecasting droughts beyond the continents." Droughts can harm or
destroy crops, as well as impact water supplies, electricity generation,
trade and ecosystem health. Historically, droughts have displaced millions
of people and cost billions of dollars. Yet the climate processes that
lead to drought are not fully understood, making accurate predictions difficult.

In order to pinpoint the large-scale landfalling droughts that originated
over the ocean, the researchers used an object tracking algorithm to
identify and follow clusters of moisture deficits all over the world,
going back decades in time. They found that the landfalling droughts
grew about three times as fast as land-only droughts, and usually took
several months to reach a continent.

"Not all of the droughts that cause damage to humans and ecosystems are
going to be these landfalling droughts," said study senior author and
climate scientist Noah Diffenbaugh, the Kara J. Foundation Professor at Stanford Earth.

"But there is something about the droughts that start over the ocean
that makes them more likely to turn into large, intense events."
The researchers analyzed the physical processes of landfalling droughts in western North America, where a high frequency of them occur. They found
that droughts that make landfall in the region have been associated with certain atmospheric pressure patterns that reduce moisture, similar to
the "Ridiculously Resilient Ridge" pattern that was one of the primary
causes of the 2012-2017 California Drought.

The authors state that further analyses may reveal similar or new
explanations for the landfalling droughts that they identified in other
areas of the world, including Chile, Argentina, New Zealand and Eastern Australia.

"Our paper shows that landfalling droughts are a global phenomenon that
affects every continent," Herrera-Estrada said. "There will definitely
be a need for other studies to focus more on the physical processes
relevant for each individual region." Because of the large humanitarian
and economic impacts of severe droughts, the potential for forecasting landfalling droughts may warrant further investigation, according to
the researchers.

"This is an important finding because these landfalling droughts
are statistically likely to be larger and more severe relative
to non-landfalling droughts," said Diffenbaugh, who is also the
Kimmelman Family Senior Fellow at the Stanford Woods Institute for the Environment. "Because they usually take a number of months to migrate
onto land, there is a potential that tracking moisture deficits over the
ocean could provide advance warning to help protect against at least
some of the most severe droughts." The research was supported by the
U.S. Department of Energy and Stanford University.


========================================================================== Story Source: Materials provided by Stanford_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Julio E. Herrera‐Estrada, Noah S. Diffenbaugh. Landfalling
Droughts: Global Tracking of Moisture Deficits From the Oceans
Onto Land.

Water Resources Research, 2020; 56 (9) DOI: 10.1029/2019WR026877 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200924114137.htm

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