One hundred and twenty nine people have now been confirmed dead in Rwanda, and another six in neighbouring Uganda, amid heavy and relentless rains which have been falling in the area since the beginning of March, triggering a series of floods and landslides. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.
Sixteen people are known to have died in a flash flood in Karongi District in Western Province, Rwanda, which swept away a number of houses at about 2 am local time on Wednesday 3 May 2023, and it is feared that more people may have died in the event and not yet been discovered. The River Sebeya, in northwest Rwanda, close to the border with Uganda, is reported to have burst its banks, leading to widespread flooding Six people, five of them from a single family, are reported to have died in a landslide in Kisoro District in the southwest of Uganda, with a number of other landslides causing disruption in mountainous areas of southern Uganda.
Rwanda has a wet montane climate, with a long rainy season which lasts from mis-September to mid-May, with two peaks in rainfall in October-November and March to April. Such a double Rainy Season is common close to the equator, where the Sun is highest overhead around the equinoxes and lowest on the horizons around the solstices, making the solstices the coolest part of the year and the equinoxes the hottest. Like other areas of East Africa, Rwanda has suffered from exceptionally high levels of rainfall this year, driven by unusually warm weather over the Indian Ocean, which means that much of the ground is now waterlogged, and cannot absorb any more water, with the effect that any further rain is likely to run over the surface leading to flooding.
The high temperatures and exceptional rainfall are thought to be associated with a developing el Niño weather-system over the South Pacific. The El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.
The development of an el Niño weather-system this year is considered particularly alarming by climate scientists, as the world has had several consecutive years in which average global sea-surface temperatures have equaled or slightly surpassed the hottest previous average temperatures recorded, despite the climate being in a la Niña phase. As sea surface temperatures are typically significantly warmer during an el Niño phase than a la Niña phase, the development of such a phase could push temperatures into areas not previously encountered on Earth since Modern Humans first appeared, potentially triggering or accelerating other climatic problems, such as glacial melting, droughts in tropical forests, and changes in ocean circulation, which might in turn take us further into unfamiliar climatic territory.
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