Warm ocean boosts East Africa’s rain in a wet season that has already left more than 130 people dead.

Kenya’s woes have just increased after a dam burst in Nakuru on Wednesday evening.

The area downstream was densely populated and, as homes were swept away, at least 10 people were killed.

Dozens remain unaccounted for, and 500 families have been affected.

Western Kenya has been particularly badly hit by landslides and floods during this season of the “long rains”.

Discussions have been ongoing about the inadequacy of infrastructure and building in vulnerable areas; nevertheless, rains have been heavier than average.

As the sun moves north with the change of season, so the Intertropical Convergence Zone (ITCZ) follows.

Low-pressure belt

This is the low-pressure belt that encircles the earth near the equator, bringing thunderstorms and moving the wet season north and south of the equator.

It is this movement of the sun that triggers the wet season, but other factors determine how much rain will fall.

In the case of Kenya and its neighbours in East Africa, the temperature of the Indian Ocean is the major factor.

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Over the past few years, the warmth of the surface layer of this ocean has increased more than that of any other.

This is almost certainly due to climate change and its effect on the flow of the slow-moving ocean currents that transport heat from the tropics to the temperate regions.

Direct measurement of the ocean surfaces is done by thermometer and satellite.

NASA’s most recent evaluation shows that for 1,000km off the coast of Somalia and Kenya, the temperature at the surface of the Indian Ocean is about 1.5C higher than average.

That equates to a larger amount of energy, or warm water, attempting to evaporate into the air above, which in turn makes showers and thunderstorms more vigorous.

More rain will fall out of every storm, and the result will be a wetter-than-average rainy season, for some.

Western Kenya benefited during this season, with the inevitable consequences.

It started off with promise for agriculture, but the rain did not stop.