Climate Outlook for the March to May 2023 Rainfall Season

March to May (MAM) constitutes an important rainfall season, particularly in the equatorial parts of the Greater Horn of Africa (GHA), where MAM rainfall contributes up to 60% of the total annual rainfall. Analysis of global climate model predictions from 7 Global Producing Centres (GPCs) customized for the GHA indicates that drier than normal conditions are most likely to continue over the drought affected regions of Ethiopia, Kenya, and Somalia. Enhanced probability for below normal rainfall is also expected over parts of Uganda, Rwanda, Burundi, Tanzania, and western South Sudan. On the other hand, wetter than normal conditions are expected over the cross-border areas of Ethiopia and South Sudan, north-western Kenya, and parts of central and southern Tanzania. In other parts of the region, including parts of central to western Kenya, north-eastern and southwestern Uganda, northern Burundi, central and northern Tanzania, and eastern South Sudan, there is no favoured rainfall category with predictions indicating equal chances of below, normal, and above normal rainfall.

The consolidated objective temperature forecast from 7 GPCs indicates an increased likelihood of warmer than normal surface temperatures over the entire region. Probabilities for warmer than normal temperatures are most enhanced over Djibouti, Eritrea, Sudan, north-western South Sudan, southern, central, and northeastern Ethiopia, northern Somalia, northern and western Kenya, and parts of south-eastern and western Tanzania.

Standardized Precipitation Index (SPI) analysis of observed and predicted precipitation for 3-, 9- and 15-month timescales ending on 31 May 2023 indicates that the extended drought in many parts of the equatorial and southern regions will continue. Notably, the 15-month SPI shows moderate to severe multi-season drought conditions in the region, particularly over Kenya, Uganda, southern Somalia, southern and south-eastern Ethiopia, southern South Sudan, Burundi, and parts of eastern Tanzania. This indicates that the long-term rainfall deficits, experienced over consecutive seasons, are expected to persist in these areas.

The predicted start of the March to May 2023 season, based on 5 Global Climate Model forecasts that provided daily outputs. There are raised chances of a delayed onset over north-eastern Tanzania and raised chances of an early onset over much of western South Sudan. Elsewhere probabilities generally favor a normal onset timing, with delayed or early onset favored only in small pockets.

The World Meteorological Organisation (WMO) and the major global climate centres have noted that Sea Surface Temperatures (SSTs) anomalies over the equatorial central Pacific Ocean are likely to return to neutral over the coming months with El Niño development becoming the most likely outcome during summer 2023. Likewise, global models further indicate that the Indian Ocean Dipole (IOD) will likely remain neutral. Updates on the El Niño Southern Oscillation (ENSO) conditions will be provided regularly by WMO and the major climate centres.

Whilst the MAM season contributes a larger fraction to the annual total for much of the GHA, seasonal anomalies are generally less predictable compared to other seasons.

This is largely a consequence of the weak linkage between rainfall and global large-scale modes of variability such as ENSO and IOD.

The outlook is relevant for seasonal timescales and covers relatively large areas. Local and month-to-month variations might occur as the season progresses. Spells of heavy rain and above normal rainfall may occur in areas with an increased likelihood of below normal seasonal totals and vice versa. ICPAC will provide regional updates on a regular basis while the National Meteorological and Hydrological Services (NMHSs) will provide detailed national and sub national climate updates.

The Climate Outlook Forum
The 63rd Greater Horn of Africa Climate Outlook Forum (GHACOF63) was convened on 22 February 2023 by the IGAD Climate Prediction and Applications Centre (ICPAC) in collaboration with the National Meteorological and Hydrological Services (NMHSs) of IGAD Member States, World Meteorological Organization (WMO), and other partners. The objective of the forum was to document and share the climate impacts across the region and formulate responses to the regional climate outlook for the March to May 2023 rainfall season over the GHA. The GHA region comprises Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, South Sudan, Sudan, Tanzania, and Uganda. The forum reviewed the state of the global climate system including the ENSO conditions, IOD, and SSTs over the Pacific and Indian Oceans, and considered their impacts on the GHA during March to May 2023 rainfall season. Climate information users from all relevant sectors (disaster risk management, agriculture and food security, livestock, health, environment, water resources, conflict, and media) as well as NGOs and development partners actively participated in the formulation of mitigation strategies.

Rainfall Outlook for March to May 2023
The rainfall outlook for various zones within the GHA region is given below.

Zone I: In this Zone (light green), the wetter than normal rainfall category has the highest probability (45%). The probability for near normal and drier than normal categories are at 20% and 35%, respectively.

Zone II: In this Zone (white color), the probabilities of below, normal, and above are equal at 33%. This equal probability zone is also considered a transition zone.

Zone III: In this Zone (orange), the below normal rainfall (drier) category has the highest probability (50%). The probabilities of the normal and above normal categories are 15% and 35%, respectively. Temperature Outlook for March to May 2023 The temperature outlook for various zones within the Greater Horn of Africa is given below.

Zone I: In this Zone (dark orange), the above normal mean temperature (i.e., warmer) category is most likely at 70%. The probability for near normal and below than normal categories are each at 15%

Zones II: In this Zone (orange), the above normal mean temperature category has the highest probability (at 65%). The probabilities of the normal and below normal categories are 15% and 20%, respectively.

Zones III: In this Zone (light orange) also, the above normal mean temperature category has the highest probability (at 55%). The probabilities of the normal and below normal categories are 15% and 30%, respectively

Note: The numbers for each zone indicate the probabilities of rainfall/temperature in each of the three categories, above-, near-, and below-normal. The top number (A) indicates the probability of rainfall/ temperature occurring in the above-normal category; the middle number (N) is for near-normal and the bottom number (B) for below-normal category. For example, in Zone III, there is 50% probability of rainfall occurring in the below-normal category; 15% probability of rainfall occurring in the near-normal category; and 35% probability of rainfall occurring in the above-normal category