Imperial College London

Climate change increased extreme rainfall in Southeast Africa storms

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photo shows two people dressed in shorts and tshirt wading through knee-deep muddy water with luggage on their heads, in the background a woman bent over as she searches for something in the water.

Aftermath of Cyclone Idai, Mozambique, 2019 (Denis Onyodi: IFRC/DRK/Climate Centre)

Experts analysing the role that climate change has played in causing extreme weather events have published the findings of a new study.

Climate change made extreme rainfall heavier and more likely to happen during several back-to-back storms in early 2022 in Madagascar, Malawi and Mozambique, according to rapid analysis by an international team of leading climate scientists.

The study by the World Weather Attribution group, which is co-led by Dr Friederike (Fredi) Otto from Imperial College London, aimed to quantify the influence of climate change on single extreme weather events, an emerging speciality known as 'attribution' science.

While the analysis shows that climate change made these events worse, the group were not able to quantify exactly how much climate change influenced the event due to a shortage of high quality weather observations available for this part of Africa.

Devastating storms cost lives

In early 2022, Southeast Africa was hit by three tropical cyclones and two tropical storms in just six weeks. Tropical Storm Ana, in late January, was followed by Tropical Cyclone Batsirai, which made landfall in Madagascar on 5 February. Over the next few weeks, the region was hit by Tropical Storm Dumako and Tropical Cyclones Emnati and Gombe.

The consecutive storms left people with little time to react. Madagascar, Malawi and Mozambique were the worst-hit countries, with more than a million people affected by extreme rainfall and floods, and 230 reported deaths. According to the World Bank, this region contains some of the world's poorest countries, where economies continue to struggle with the effects of the COVID-19 pandemic.

Dr Piotr Wolski, Climate System Analysis Group, University of Cape Town and co-author of the study, said: "Southeast Africa, including Madagascar, Malawi and Mozambique, is already a hotspot for tropical storms and cyclones, which we expect to become more intense and destructive with climate change."

To evaluate the role of climate change on the frequency and intensity of extreme rainfall during the storms, the scientists used peer-reviewed methods to analyse weather observations and computer simulations to compare the climate as it is today - after about 1.2°C of global warming since the late 1800s - with the climate of the past.

Warmer atmosphere means more downpours

The analysis focused on rainfall, which caused widespread flooding, over the wettest three-day periods in two regions: Madagascar, where cyclone Batsirai caused major damage, and an area over Malawi and Mozambique most affected by Tropical Storm Ana. In both cases, the results show that rainfall associated with the storms was made more intense by climate change and that episodes of extreme rainfall such as these have become more frequent.

The finding is consistent with scientific understanding of how climate change, caused by human greenhouse gas emissions, influences heavy rainfall. As the atmosphere becomes warmer it accumulates more water, increasing the risk of downpours. With further greenhouse gas emissions and continued temperature increases such heavy rainfall episodes will become even more common.

Dr Fredi Otto, Senior Lecturer in Climate Science at the Grantham Institute - Climate Change and the Environment at Imperial College London, said: "Again we are seeing how the people with the least responsibility for climate change are bearing the brunt of the impacts. Rich countries should honour their commitments and increase much-needed funding for adaptation, and for compensating the victims of extreme events driven by climate change with loss and damage payments."

Lack of climate data from African regions

While the analysis shows that climate change made the events more intense and damaging, the precise contribution of climate change to the event could not be quantified, due to the absence of comprehensive historical records of rainfall in the region. Of 23 weather stations in the affected area in Mozambique, only four had relatively complete records going back to 1981. In Madagascar and Malawi there were no weather stations with suitable data for the study.

Dr Sarah Kew from the Royal Netherlands Meteorological Institute, and a co-author of the study, said: "While our analysis clearly shows that climate change made the storms more damaging, our ability to establish precisely by how much was hampered by inconsistent data and lack of weather observations. This would also help to improve forecasts of extreme weather events and their impacts"

In many other parts of the world where more comprehensive weather station data is available, scientists have been able to quantify the influence of climate change on particular extreme events. Increased investment in weather stations in Africa would enable a more precise estimate of the impact of rising greenhouse gas concentrations on the continent.

Dr Izidine Pinto from the Climate System Analysis Group at University of Cape Town and Red Cross Red Crescent Climate Centre, also a co-author of the study, said: "Strengthening scientific resources in Africa and other parts of the global South is key to help us better understand extreme weather events fueled by climate change, to prepare vulnerable people and infrastructure to better cope with them."

Roop Singh from the Red Cross Red Crescent Climate Centre, and a co-author of the study, said: "This study confirms what Red Cross and Red Crescent volunteers have been saying for a long time, that the rains have changed. They are more intense and there is less time for people to recover before the next disaster hits. We need to invest in the infrastructure, systems, and people who are most vulnerable so that they can withstand stronger storms and compounding risks."

The study was conducted by 22 researchers as part of the World Weather Attribution group, including scientists from universities and meteorological agencies in France, Madagascar, Mozambique, the Netherlands, New Zealand, South Africa, the United Kingdom and the United States.

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Reference:

"Climate change increased rainfall associated with tropical cyclones hitting highly vulnerable communities in Madagascar, Mozambique & Malawi", Friederike E. L. Otto, Mariam Zachariah, Piotr Wolski, Izidine Pinto, Rondrotiana Barimalala, Bernardino Nhamtumbo, Remy Bonnet, Robert Vautard, Sjoukje Philip, Sarah Kew, Linh N. Luu, Dorothy Heinrich, Maja Vahlberg, Roop Singh, Julie Arrighi, Lisa Thalheimer, Maarten van Aalst, Sihan Li, Jingru Sun, Gabriel Vecchi, Luke J. Harrington

See the press release of this article

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Simon Levey

Simon Levey
The Grantham Institute for Climate Change

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Email: s.levey@imperial.ac.uk

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