How the Famine Early Warning Systems Network Developed Its Rainfall Outlook to Warn of Drought in Eastern Horn of Africa

USAID Responds to Drought Warnings in Eastern Horn of Africa

Following a Joint Alert on exceptional drought conditions and related acute food security risks in the eastern Horn of Africa, USAID announced it will provide more than $39 million in additional humanitarian aid to the region, urging other donor organizations to follow suit.

The Famine Early Warning Systems Network (FEWS NET), one of four agencies that issued the Joint Alert, has warned since late 2021 that very high humanitarian assistance needs are likely to persist in the eastern Horn of Africa throughout 2022. In a regional consultation on the March-April-May (MAM) rainy season in January, FEWS NET stressed that a below-average rainy season in 2022 is likely.

Ahead of USAID’s announcement, FEWS NET urged a “no-regrets approach” in responding to a predicted fourth consecutive below-normal rainfall season and consequential increases in food insecurity.

FEWS NET Agroclimatologist Explains Science Behind Seasonal Rainfall Outlooks

Forecasting potential instances of severe drought and related food insecurity requires a rigorous approach to developing outlooks for seasonal rainfall performance. Senior agroclimatologist, Dr. James Verdin, explained how FEWS NET developed its seasonal rainfall outlook for the eastern Horn of Africa.

“Global climate models are the tools that everyone uses to develop outlooks for seasonal rainfall performance,” Verdin explained. “There are many such models, and no single model forecast is relied upon because there is such large variability among them.”

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Map of seasonal rainfall outlook for the eastern Horn of Africa

Photo Credit: USAID

According to Verdin, averaged “ensemble” models simulate the circulation of the oceans and atmosphere, providing insight into the potential for rainfall in the months ahead. In the Horn of Africa, while models do well forecasting the performance of the October-November-December rains, they are not as skillful in predicting performance of the MAM rains. However, by analyzing large-scale patterns of ocean temperatures, agroclimatologists can explain much of the variability in seasonal rainfall in the Horn of Africa.

“Ocean water is much denser than air, so it moves and changes temperature more slowly than air, making its movements and temperature changes easier to simulate,” Verdin said. “The idea is to identify years in the past that had sea surface temperature (SST) patterns in the tropical Pacific and Indian Oceans similar to model forecast SST patterns, and then examine the MAM precipitation outcomes for those analog years.”

This technique of comparing oceanic temperature patterns to precipitation was used to predict a fourth consecutive below-average rainfall season across the eastern Horn of Africa in MAM 2022, according to Verdin. While precipitation maps from the last 11 analog years display varied wet/dry patterns, only 2006 and 2018 showed predominantly wet outcomes.

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Maps from 1999 to 2021 of historical analog years with similar global sea surface temperature patterns

Photo Credit: USAID

“MAM 2022 will see an outcome with its own unique wet/dry pattern. We don’t know what it will be,” Verdin said. “It could look like 2006 or 2018, but it’s more likely to have significant areas of drought like the other nine analog years.”

Despite the uncertainty, Verdin explained that taking a “no-regrets approach” in responding to the potential for continued drought in the region would be the safest bet.

“We would be better off preparing for a dry outcome and being pleasantly surprised if the rains perform well, rather than counting on good rains only to experience a fourth consecutive drought,” he said

Joint key messages from the January 2022 regional consultation regarding the outlook for the MAM 2022 rainy season in the Horn of Africa. Participating organizations included the Food and Agriculture Organization (FAO), FEWS NET, the World Food Programme (WFP), the Intergovernmental Authority on Development (IGAD) Climate Prediction Applications Center (ICPAC), World Meteorological Organization (WMO), and the United Kingdom Meteorological Office (UK Met Office):

Horn of Africa, Eastern sector:   

• Above-average land surface temperatures in the eastern Horn and northern sector are forecast until the start of the next rainy season. This will likely drive a quicker-than-usual deterioration in rangeland conditions and continued poor pastoral conditions for livestock through at least March 2022.
• The March to May rainy season (long rains) is notoriously difficult to forecast with global models, which showed high levels of uncertainty for most of the region. However, some recent analog forecasts, based on the analysis of Pacific March-May sea surface temperatures, past droughts and a number of previous La Nina years, suggest the possibility of another below-average season in 2022. If this were to occur, it would result in an unprecedented (in the last 40 years) sequence of four below-normal rainfall seasons, and major increases in food insecurity would be expected.
• Given already high levels of acute food insecurity due to the drought and other drivers, a “no-regrets approach” to the response is urgently needed to respond to the current severe drought conditions and the possibility that another below-average season may occur.

Horn of Africa, Western sector:

• There is an increased probability of above-average to average rains.

This blog was originally published on Agrilinks. To get the latest updates on East Africa, follow @FEWSNET on Twitter and Facebook, or subscribe to receive updates on the countries and/or topics of your choice.