La Niña brings drought to the Horn of Africa

Wednesday 06th Jul 2011 by theWeather Club

The Horn of Africa, comprising of Ethiopia, Eritrea, Somalia, Djibouti, Kenya and Uganda, usually experiences two rainy seasons a year: the first between March and May and the second from October to December.

In 2010 the rainfall was erratic during November and December was hot and dry leaving two thirds of Somalia with less than 75% of their average rainfall. This shortage of rain during October to December is a classic consequence during a La Niña phase which was particularly strong towards the end of 2010. La Niña is a cooling in the surface waters in the central and eastern Pacific Ocean which leads to relatively warmer water in the western Pacific, bringing heavy rain to eastern Australia, the Philippines, and Indonesia. This domino-style effect temporarily changes the weather patterns with an increase in the intensity of westerly winds over the Indian Ocean transferring moisture away from East Africa. The strong La Niña conditions eased during the first half of 2011 but still impacted on the spring rainfall which was lacking and has led to the worst drought in 60 years.

La Niña, and the opposite warming phase known as El Niño, lead to natural changes in the climate around the world but new research from the University of California in Santa Barbara (UCSB) highlights that climate change is the increase the frequency of droughts across East Africa in the coming years. Their studies found that as the global temperature has risen in recent years, the Indian Ocean had warmed faster than many other parts of the world. A warmer Indian Ocean will produce more rain that falls over the ocean but reduce the amount of rainfall over East Africa.