Climate change made extreme rainfall heavier and more likely to happen during several back-to-back storms earlier this year in Madagascar, Malawi and Mozambique, according to rapid attribution analysis by an international team of leading climate scientists.
While the analysis shows that climate change made the eventsworse, the scientists 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.
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.
To evaluate the role of climate change on the frequency and intensity of extreme rainfall during the storms, the scientists analysed 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, following peer-reviewed methods.
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.
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.
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.
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 UK and the US