The main rainy season in Somalia was deficient in 2016. Then the important short rains of October to November 2016 failed, causing crop failures and severe food shortages.

A report this month from the International Committee of the Red Cross warned that "the humanitarian situation in Somalia is on the verge of catastrophe, and concern is growing that the trajectory is worryingly similar to Somalia's 2011 famine disaster, when an estimated 260,000 people died. Today, an estimated 6.2 million, more than half the country's population, face acute food shortage and the number of severely malnourished children is on the rise."

Drought is also affecting neighbouring countries, with some 16 million people severely food insecure in the Horn of Africa region: 5.6 million people in Ethiopia, 2.6 million people in Kenya, 6.2 million people in Somalia and 1.6 million people in Uganda.

Human population and agricultural practices affect water usage and distribution, but the climate brings the rain, and the climate is changing. Over the past 30 years, the long rains have been steadily decreasing in intensity as the climate has warmed.

East Africa has two rainy seasons; the critical "long rains" of March to June, connected to the development of the Indian monsoon, and the less critical but still important "short rains" of October to November.

The 2016 rainfall failure was due to the negative "Indian Ocean Dipole" (IOD). This is the name describing cooler than average waters in the western Indian Ocean, and warmer than average waters in the Eastern Indian Ocean. A negative IOD causes stable, sinking air over the Horn of Africa and this suppresses any rain-bearing clouds.

The Indian Ocean Dipole (IOD) index went sharply negative during the second half of 2016 in a probable response to the Pacific Ocean's rebound from the earlier El Nino. Fortunately for the East African rainy season, the IOD is predicted to move through neutral to positive territory during 2017.

During the first week of April, the rains finally began in southwestern Sudan, with daily amounts up to 25mm common. The "long rains" are forecast to arrive in Somalia imminently. Six out of eight seasonal rain forecast models are suggesting a near-average to above-average wet spell in May and June in Somalia.

With thanks to Jeff Masters, Weather Underground.