More and more storms torment Sahel: climate study

Africa's Sahel region has seen a three-fold increase since 1982 in destructive rainstorms that bring misery rather than relief, said a study Wednesday that pointed the finger at climate change.

And unless global warming is halted, this vast semi-arid region will endure ever more frequent downpours that flood homes and crops and breed killer germs in countries with insufficient public infrastructure to fight back.

"We were shocked to see the speed of the changes taking place in this region," said Christopher Taylor, a meteorologist at the Centre for Ecology and Hydrology in Lancaster, England, who took part in the study.

Taylor and a team used satellite observations of clouds from 1982 to 2016 to track the evolution of storm patterns in the region south of the Sahara Desert, including parts of Senegal, Mauritania, Mali, Burkina Faso, Niger, Nigeria, Chad, and Sudan.

The researchers found that destructive storms known to meteorologists as "mesoscale convective systems" (MCS) grew in frequency from about 24 per rainy season in the early 1980s, to about 81 today.

The rainy season lasts from about June to September.

In the Sahel, MCS events are "some of the most explosive storms in the world", said the researchers, who presented their findings at a meeting of the European Geosciences Union in Vienna.

The storms supply about 90 percent of the region's rainfall -- but more tempests do not equate to more water.

"We are not reporting a 'good' outcome," Taylor told AFP by email.

While storms have become more frequent, annual average rainfall has remained unchanged for at least 15 years, he said.

"More intense rain means more water runs off and does not infiltrate into the soils where crops could benefit," Taylor explained.

It also washes away nutrient-holding agricultural soil in a region still recovering from a historic 20-year drought between the 1970s and 1990s.

- Warmer Sahara -

Abdoulaye Diarra of the International Institute for Water and Environmental Engineering, in Ouagadougou, said cities with poor drainage systems are also hard hit by MCS events.

Floods in Burkina Faso in September 2009 saw more than 50 percent of the capital, including its main hospital, deluged when more than 263 millimetres (10 inches) of rain fell in a few hours.

"Eight people died, more than 250 houses and 670 classrooms were destroyed, the main water purification plants for the city were out of use and nearly 150,000 people were affected," Diarra wrote in comment on the study, whose findings were published in the journal Nature.

The research team was surprised to find that neither temperatures nor air humidity in the Sahel region rose in step with the increase in storm intensity.

Usually, global warming is predicted to make storms more intense because there is more water-holding, warm air -- the fuel for torrential downpours.

But looking beyond the Sahel, the team found their smoking gun in higher average land temperatures globally, and in the vast desert to the region's north.

This finding "warns us that it may not be changes in local temperatures which drive changes in rainfall," said Taylor.

"In this instance it is the rapid warming of the Sahara which we think is responsible."

Linking a past or current weather event to global warming with any certainty is a particular headache for climate scientists.

But the consensus is that storms, floods, and droughts will become worse overall if planet-heating continues.

The world's nations agreed in Paris in 2015 to limit average surface warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels.

This will be achieved by curbing the use heat-capturing greenhouse gases emitted by the burning of oil, coal and gas.