Imma Perfetto
Cosmos science journalist
In some regions of the world, including parts of Africa, Asia, Americas and Australia, the conditions are right for megastorms to form.
These weather systems, known as “Mesoscale Convective Systems” (MSCs), span thousands of square kilometres and are accompanied by extreme weather conditions, such as destructive winds, lightning, flash flooding and hail.
According to Dr Emma Barton, a meteorologist at the UK Centre for Ecology & Hydrology: “MSCs are some of the most intense thunderstorms on the planet, and they are increasing in severity due to climate change.”
Barton is first author of a new study in Nature Geoscience, which has identified a new driver of larger megastorms: soil moisture.
By analysing satellite data collected from 2000-2019, Barton and her collaborators discovered that soil moisture can alter atmospheric conditions, and subsequent storm size and rainfall in West Africa, India, South America, South Africa, Australia and the US Great Plains.
Specifically, large contrasts in soil moisture over ranges of hundreds of kilometres strengthens atmospheric temperature gradients and leads to stronger shifts in wind direction and or speed higher up in the atmosphere. This favours larger storms that produce more rainfall.
This increase in rain ranges from 10 to 30% depending on the region and size of the storm.
“Rising temperatures could increase the contrast between wet and dry areas of soils, further intensifying thunderstorms in already severely impacted regions,” says Barton.
Additional analysis of West Africa, India, South Africa and South America, which had sufficient storm data, revealed the surface soil conditions which strengthen these storms are present for 2–5 days before they hit.
Integrating satellite observations of soil moisture into forecasting could improve advance warning of potential hazards such as flash flooding. The researchers say this will be particularly important in “data-sparse and climatically exposed regions such as Africa, where 60% of the population currently lack early warning systems.”
“Understanding how soil moisture influences storm activity, and how this may change in the future, will be essential for more accurate short-term forecasting to warn communities about approaching storms, as well as making longer-term projections,” Barton says.
However, the researchers caution that the strength of the relationship between soil moisture and storm properties is likely different for each region.
“Therefore, the potential improvement in forecasting that can be achieved by accounting for surface conditions will also vary by region,” they write.
The next step is to explore what factors contribute to these regional variations.
