Heavy downpours in Kenya paralyzed Nairobi for over three days. The Intertropical Convergence Zone is a planetary scale band of heavy rains that encircles Earth near the equator. It is where northeast trade winds and Southeast trade winds collide.
Climate change will move this band northward as the planet heats—increased extreme swings of the Atlantic intertropical convergence zone in a warming climate.
Interannual variability of the Atlantic intertropical convergence zone (ITCZ) affects hydrological cycles, extreme weather events, ecosystems, agriculture and livelihoods in Atlantic-rim countries. It can experience an interannual extreme swing, moving hundreds of kilometres northwards during boreal spring, causing severe droughts in central-eastern Amazon and floods in northern South America. How its interannual variability will respond to global warming remains unknown. Here using state-of-the-art climate models under a high-emission scenario, we project a more-than-doubling increase of extreme northward swings. This increase from one event per 20.4 years in the twentieth century to one per 9.3 years in the twenty-first century is underpinned by a mean state change of sea surface temperature, with faster warming north of the Equator. The warming differential facilitates the increased frequency of extreme swings, as the ITCZ follows the maximum sea surface temperature. Our finding suggests a substantial increase in ITCZ swing-induced severe droughts/floods in the Atlantic-rim countries.
Climate change is a threat multiplier as the atmosphere can hold more moisture due to warming oceans. Additionally, it is a man-made disaster due to decades of lack of planning and mismanagement. Kenya received close to eighteen inches of rain over three days; hundreds are dead in Kenya, Burundi, and Tanzania. Heavily populated Nairobi suffered severe damage as streets turned to raging rivers.
Hundreds of people in Tanzania and Kenya are dead after heavy rain during the region's monsoon season, officials said.
Flooding in Tanzania caused by weeks of heavy rain has killed 155 people and affected more than 200,000 others, the prime minister said Thursday.
That is more than double the number of deaths reported two weeks ago as the amount of rainfall increases, especially in the coastal region and the capital, Dar es Salaam. Flooded schools have been closed and emergency services have rescued people marooned by the flood waters. Roads, bridges, railways and other infrastructure have also been destroyed, officials said.
Prime Minister Kassim Majaliwa warned those living in low-lying areas to move to higher ground and urged district officials to ensure that provisions meant for those whose homes were washed away go to those in need of the supplies. He said more than 51,000 households have been affected by the rains.
One of the biggest drivers of heavy rain in East Africa is the Indian Ocean Dipole (IOD).
The IOD - often called the "Indian Niño" because of its similarity to its Pacific equivalent - refers to the difference in sea-surface temperatures in opposite parts of the Indian Ocean.
During a positive phase the waters in the western Indian Ocean are much warmer than normal and this can bring heavier rain regardless of El Niño.
However, when both a positive IOD and an El Niño occur at the same time, as was the case last year, then the rains in East Africa can become extreme.
One of the strongest positive IOD patterns on record coincided with one of the strongest El Niño patterns in 1997 and 1998, with severe flooding reported. These caused more than 6,000 deaths in five countries in the region.