New research will improve early warning of devastating megastorms

Mesoscale convective systems (MCSs) are 'megastorms' that affect large parts of the world, including Africa, Australia, Asia and the Americas, causing human and livestock deaths plus major damage to infrastructure. They can potentially:

• last from several hours up to two days
• release energy equivalent to the UK consumption for an entire year
• be bigger than the size of England and travel 1,000kms in distance
• unleash over 100mm of rainfall in just an hour

In Sahelian Africa, these extreme storms have tripled in frequency since the 1980s due to global warming.

Until now, it was thought that the path of these complex weather systems was largely unpredictable.

However, a new study by the UK Centre for Ecology & Hydrology (UKCEH) has found that land surface conditions frequently affect the direction and intensity of megastorms after they have formed.

The research is now helping scientists to develop online tools to better forecast the path and strength of an approaching storm, which will inform alert systems for communities across Africa, providing them with up to six hours' warning. This includes Senegal, where UKCEH is working with the national meteorological service, ANACIM, to see how useful very short-term forecasts are for local emergency responses.

The new study, published in the journal PNAS, was funded by the Department for International Development (DFID) and Natural Environment Research Council (NERC) as part of the UK aid Future Climate for Africa research programme.

The researchers looked at satellite data on the activity of thousands of storms, plus land temperatures, in the Sahel for the period 2006 to 2010.

Lead author Dr Cornelia Klein of UKCEH explains: "It is well known that heat provides thunderstorms with great energy, but it was commonly thought that once they are moving, they were not affected by the state of the ground over which they travelled.

"However, we found that drier soils increased the intensity of an MCS mid-storm, affecting the amount of rainfall they release and also where they travel. Conversely, we found storms were often weakened over moister soils."

"Our finding means that, for the first time, we can predict, from satellite-observed surface conditions, how these extremely large West African storms may behave when, for example, they approach a city. A more effective alert system will enable local people to take action to protect themselves as well as their homes, livestock and possessions, plus plan emergency responses."

Flash flooding frequently occurs during the storm season in the Sahel, peaking between June and September, and can have a serious impact, with water entering homes and people losing property and a safe, dry space to live. Flooding can also cause sewage overflow from inadequate drainage systems, posing a health risk to humans and animals.

The study's authors say the results have important implications for 'nowcasting' (forecasting for several hours ahead) of severe weather not just in the Sahel, but potentially other MCS hotspot regions of the world.

Professor Chris Taylor of UKCEH, co-author of the new paper, adds: "The pattern of these megastorms is supposed to be difficult to forecast but we found a surprising level of predictability. Very dry soils influenced around half of storms in late afternoon or early evening, when they are at their peak.

"Further research and advances in satellite technology will increase our certainties about their movement. In decades to come, scientists will look back at this latest study as a gamechanger in the reliable forecasting of these devastating storms."

The research is part of the UKCEH-led AMMA-2050 project, which is carrying out multidisciplinary climate research to support improved forecasting, in order to enable better decision making by town planners, farmers and communities. Comprising partners from Europe and West Africa, it is funded by DFID and NERC.

A DFID spokesperson said:

"Highly destructive megastorms are becoming much more common because of climate change. They can devastate entire communities and it is the world's poorest people who are most at risk.

"UK aid is supporting ground-breaking research, led by British experts, to better anticipate storms so vulnerable African communities can better prepare for their impact, protecting themselves and their families, and making their economies more resilient to climate shocks."

Recent flooding events in West Africa

• Due to heavy flooding in the countries of Niger and Mali since June 2020, 19 people are reported to have died and 35 injured, with 2,244 houses destroyed. An estimated 112,452 people are at risk of being affected by floods in Mali this year, compared to 95,000 people last year. During the rainy season in Niger in 2017, estimated 200,000 people were affected by flooding in the country, with 56 deaths. About 12,000 houses were damaged and 16,000 heads of cattle died and 9,800 hectares of cultivated land lost.
• In late July 2020, it was reported at least seven people died in flooding in the Niger state in central Nigeria, while 15,000 people were displaced in northern Nigeria in the first week of August after flooding damaged homes.
• Ouagadougou, capital of Burkina Faso, has been regularly hit by flash flooding in recent years. In July 2020, crocodiles were seen in the streets after torrential rain forced them from their habitat at a nearby city park.

Thousands of people were displaced in northern Burkina Faso in mid-June 2020 after shelters were damaged there. Ouagadougou, the country's capital, has been regularly hit by flash flooding in recent years. In 2009, a downpour of 263mm over several hours forced 150,000 residents to leave their homes and eight people were killed. Within a few weeks in mid-2016, heavy rain and strong winds caused flash floods, leaving 15 dead and severely affecting healthcare facilities.

• In 2012, there was over 140mm of rainfall within a single hour in Dakar area of Senegal, producing floods which affected more than 250,000 people, with 26 deaths. Similar flooding in the Dakar region in 2009 affected an estimated 30,000 houses, with losses of US $82m.