Mostly beneficial impacts of above average rainfall in East Africa

• The March to May, seasonal rains are likely to conclude on time with largely above-average rainfall across the region, with the exception of areas in bi-modal South Sudan and Uganda that continue to have cumulatively below average rainfall.
• In the Horn, rainfall in late April and into May was characterized as exceptionally heavy causing severe flooding, displacement, property damage, and deaths. In the southeastern part of the region, this was aggravated by the atypically close passage of two cyclones, Hidaya and IALY, to the coastal strips of Tanzania and Kenya.  
• Overall, the abundant rains have been very beneficial for the current agricultural season in medium and high maize productive areas of East Africa. The seasonal rains also created favorable conditions for timely planting of long-cycled crops in areas of central and northern Ethiopia. Rangeland resources (pasture and water) are equally exceptional across the Horn.
• In Uganda, the record high water levels in Lake Victoria and the Nile River basin prompted the Ugandan Government to release large volumes of water from the Jinja dam in early May. When combined with the forecast of La Niña-induced above average rainfall, this volume of water in the White Nile is expected to further aggravate already anticipated severe flooding downstream in South Sudan, as well as in Sudan, during the June to September rainy season. 
• Moderate to locally heavy rains are expected across the region in the next 2 weeks, particularly along the coastal strip and western sectors of the region. The June rainfall forecast indicates a high likelihood of above average rainfall across the region.

Context: Between March and May, the following are the areas and names of the rainy seasons underway in parts of East Africa: Gu rains in Somalia; long rains in unimodal Uganda, Kenya, Burundi, and Rwanda; belg rains (mid-February to May) in Ethiopia, as well as the diraac/sugum rains in the northern pastoral area and gu/genna rains in the southern and southeastern pastoral areas of Ethiopia; and the first season rains in the bimodal zones of southwestern South Sudan and northern Uganda.

As the March to May Season comes to an end, it has been characterized by mixed onset and varied cumulative rainfall. In the southeast regions, coastal Kenya, and eastern parts of Tanzania, the onset of the rains was timely, and rainfall was above average seasonally across the region. By contrast, parts of Uganda, Rwanda, and some areas of bi-modal South Sudan experienced a delayed onset and cumulatively below average rainfall to-date compared to the long-term average (Figure 1). In Ethiopia, the belg/gu/genna season has seen generally above-average rains leading to favorable crop production prospects as well as abundant water and pasture availability in the pastoral regions.

Between mid-April and early May, the exceptionally above-average rains, especially in the eastern parts of the region, led to deadly flooding in parts of southern Burundi, central and eastern regions of Kenya, coastal Tanzania, northern and southern Ethiopia, southern Somalia, and parts of Uganda that claimed approximately 470 lives, displaced almost 410,000 people, and caused damage to unaccounted amount of property. Overall, more than 2 million across the region were reportedly affected, approximately 560,000 of whom are in Ethiopia. This excessive rainfall was mostly attributed to two key elements: (1) the interaction between the tropical and the mid-latitude frontal systems, and (2) the intense sequential tropical cyclones that came uncharacteristically close to the Tanzania/Kenya coast. 

However, the impact of the flooding on crop production was reportedly relatively limited. For example, in Kenya, the flood and crop-water-logging damage is currently estimated at 62,000 acres, which represents approximately just 1 percent of the average national maize acreage of 5.1 million acres. In other regions affected by flooding, households are replanting or waiting for flood waters to recede so that they can replant. 

Moreover, vegetation conditions across the region are generally very good due to the above average rainfall, as depicted by the eVIIRS Normalized Difference Vegetation Index (NDVI) in Figure 2, providing beneficial pasture and water for pastoralists. The soil moisture as of the end of April has also been favorable at depths of 100 cm, which is critical for deep-rooted vegetation and crops, and crop conditions are average to very good across most of East Africa per the extended Water Requirement Satisfaction Index (WRSI) as of May 11-20 period (Figure 3). 

Currently, most of the flood waters have receded across Kenya, Tanzania, Burundi, Somalia, and Ethiopia. However, the coastal regions of Tanzania, Kenya, and Somalia have been threatened by two cyclones within 4 weeks, which have spurred additional flood alerts for these areas. Looking forward, the release in early May of large volumes of water from the Jinja dam in Uganda, estimated at 2,400 cubic meters per second, due to record high water levels in Lake Victoria and the River Nile Basin, is expected to further aggravate already anticipated severe flooding in South Sudan and Sudan during the upcoming main rainy season (June to September) when La Niña induced above-average rainfall is forecast. 

The June rainfall outlook, based on NMME one-month forecasts (Figure 4), are indicative of continued moderate to locally very heavy rains over western Ethiopia, most of South Sudan, Uganda, Rwanda, and central and western Kenya, as well as parts of southern Somalia. This will likely improve the conditions in Uganda and Rwanda which had a slow start and below average rainfall earlier in the season.  Seasonal rains over parts of eastern Horn are likely to gradually subside into dry and hotter-than-normal conditions as southern Somalia and the East Africa coastal strip rainfall peaks normally in May into June. The northern sector of the region is also forecasted to have above average rainfall which will likely lead to an early onset of the Kiremt and the unimodal June through September (JJAS) cropping season. Global climate prediction centers forecast a transition from ENSO neutral to La Niña phase in May-June 2024. Thus, the northern sector of East Africa (unimodal South Sudan, Sudan, and Kiremt-receiving areas of Ethiopia) is highly likely to receive above-average rainfall during the coming June to September rainy season.