NAIROBI, Kenya (AP) — The torrential rains and deadly floods that have hit Kenya since March have been among the country’s most catastrophic in recent years.
According to the latest government figures, at least 169 people have died as a result of the heavy rains and more than 91 are missing.
In the single most tragic event, at least 48 people died on Monday after water blew through a blocked river tunnel under a railway bridge in southwestern Kenya, causing a flash flood. The rain displaced more than 100,000 people and damaged roads and other infrastructure.
The devastating rains are the result of a combination of factors, including the country’s seasonal weather patterns, man-made climate change and natural weather phenomena.
Here’s how they worked together to cause the deadly flood.
WHAT IS KENYA’S “LONG RAIN” SEASON?
In Kenya and some other parts of East Africa there are two main rainfall seasons: the “long rainy season” from March to May and the “short rainy season” from October to December.
The “long rain season” receives most of the country’s average annual precipitation. It is often characterized by heavy rainfall and sometimes lasts into June.
In its forecast for this year’s “long rainy season”, the Kenya Meteorological Department predicted above-average rainfall for many parts of the country, with occasional storms in some. There were also warnings of flash floods, landslides, mudslides and other impacts.
Last year’s “Short Rains” season was characterized by severe storms in many parts of the country, particularly in November. Lamu, Mombasa and Garissa counties recorded almost three times their long-term average rainfall. according to the meteorological department.
Why is it raining so heavily this time?
The frequency, pattern and intensity of rainfall in Kenya is influenced by naturally occurring climate systems such as the Indian Ocean Dipole.
The Indian Ocean dipole is a fluctuation in sea surface temperatures that makes the western Indian Ocean warmer than average and then colder than average than the eastern Indian Ocean. There are positive, neutral and negative phases.
The positive phase leads to heavy rainfall in areas west of the Indian Ocean such as Kenya and droughts in Indonesia and Australia.
While many people associate the current floods with the naturally occurring weather phenomenon El Niño, research shows that the climate event has little impact on rainfall over East Africa during the “long rainy season,” said Joyce Kimutai, a research fellow at Imperial College London.
El Nino is the warming of the ocean over the Pacific Ocean that changes the routes for storms and can cause heavy rainfall in some parts of the world and drought in others.
But in the case of Kenya, it is very likely that the positive Indian Ocean dipole and climate change explain the ongoing flood-triggering rains, she said.
Warmer oceans caused by the hotter atmosphere increase evaporation, and air containing more moisture can lead to more intense precipitation.
In an analysis last December, Kimutai and colleagues from World Weather Attribution, a group of scientists who analyze whether climate change plays a role in extreme weather, found that human-caused climate change led to “brief rains” in last year Kenya had led and in other parts of East Africa up to twice as intensive.
When will the “long rains” end?
It has become difficult to predict long-term weather in Kenya in recent years due to increasing changes in the start and duration of the dry and wet seasons.
The Kenya Meteorological Department expected The “long rainy season” lasts until June.
In its latest seven-day weather forecast released on Monday, the ministry said it expected rain to continue in several parts of the country, with heavy rain expected in six regions, as well as flooding in low-lying areas and landslides in steep slopes.
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