Heavy rains in the East African region explained

The current heavy rainfall being experienced across the country and the East African region are as a result of a phenomenon in the Indian Ocean known as the Positive Indian Ocean Dipole(IOD).

The Indian Ocean Dipole describes an irregular oscillation or variation of Sea Surface Temperatures (SSTs) between the Eastern and Western parts of the Indian Ocean.

The East Africa region lies on the Western part of the Indian Ocean while countries like Australia and Indonesia are on the Eastern part of the Indian Ocean.

A Positive Indian Ocean Dipole (irregular oscillation or variation of Sea Surface Temperatures) occurs when the western part of the Indian Ocean becomes significantly warmer than the eastern side of the Indian Ocean.

A Negative Indian Ocean Dipole occurs in the reverse; areas in the Eastern Indian Ocean over Australia and Indonesia are warmer while the Western Indian Ocean will be experiencing cooler conditions.

“Cool sea surface temperature lead to a stable atmosphere which inhibits and hinders the escape of water vapour into the atmosphere.”

In a positive Indian Ocean Dipole in which Sea Surface Temperatures in Western Indian Ocean are warmer, forming a low pressure cell, this then makes it possible for winds to move from the high pressure cell in the Eastern Indian Ocean which is cooler blowing over the warm air in the Western Indian Ocean that then dumps the evaporated warm are that then forms rain that falls in the region.

“Warm Sea Surface Temperatures lead to enhanced evaporation rate with more water vapour escaping into the atmosphere leading to formation of clouds hence the high amount of rainfall experienced.”

In a negative IOD phase, one observes cooler sea surface temperatures in western Indian Ocean, resulting in drier conditions over much of East Africa.

During negative IOD, Kenya and East Africa in general is associated with depressed rainfall. This may also lead to Drought situation. During this time regions to the east of the Indian Ocean experience very wet conditions. Hence the term oscillation, the situation oscillates from Eastern Indian Ocean to Western Indian Ocean and vice versa.

The neutral phase of Indian Ocean Dipole occurs when there is no significant variation of sea surface temperatures between Western and Eastern parts of Indian Ocean.

According to climate scientists, in the 20th century, the Indian Ocean Dipole occurred once every 17 years, “but it is increasing in its occurrence due to climate change.”

In its recent forecast, the Kenya Meteorological Department has indicated that the country will experience continued heavy rainfall from 4th December 2019 at 3am to 6th December 2019 at 3pm and reduce in intensity over the weekend.

According to the Weatherman, counties that will be most affected incude; Narok, Kajiado, Bomet, Kericho and Nakuru.

The others are; Migori, Nyamira, Kisii, Homa Bay, Kisumu, Siaya, Busia, West Pokot, Uasin Gishu, Baringo, Nandi, Trans Nzoia and Bungoma. The rest indluce; Kakamega, Elgeyo Marakwet, Nairobi, Nyeri, Embu, Meru, Laikipia, Kiambu, Nyandarua, Murang’a, Kitui, Taita Taveta, Machakos and Makueni.

The Advisory signed by the Deputy Director of Meteorological Services Dr. David Gikungu is advising the public to look out for potential floods in the areas listed.

“As flood waters may suddenly appear even in places where it has not rained heavily and may be deeper and faster than they look,” said Dr. Gikungu in the advisory and added, “avoid walking in moving water, in open fields or sitting near grilled window panes, so as to minimize exposure to lightning strikes.”

The weatherman also advised motorists to avoid driving through moving water to avoid drowning.

He asked those in landslide prone areas to be on alert, saying the Abardares Ranges, Mt. Kenya and hilly areas in the Western Kenya region are prone to landslides and made worse by the current “saturated soils owing to heavy rainfall which could move down slope as friction has been reduced by the presence of water in the soil.”


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