Statement from the Twentieth Greater Horn of Africa Climate Outlook Forum, 5-6 September 2007, Nairobi, Kenya
Summary
There is increased likelihood of near-normal rainfall over much of the Greater Horn of Africa during the September to December 2007 season. A high likelihood of near normal to below normal rainfall is indicated over central and extreme northeastern Sudan; much of Eritrea; northwestern, southeastern and eastern Ethiopia; eastern Djibouti; much of Somalia; much of Kenya; eastern Uganda; eastern and central Tanzania; northern Burundi and western Rwanda. Southern Sudan; western, central and northeastern Ethiopia; extreme northwestern Somalia; northwestern and southwestern Kenya; much of Uganda; central and eastern Rwanda; central and southern Burundi; as well as northern and western Tanzania have increased likelihood of near-normal to above normal rainfall. It should be noted that heavy and short duration episodic events and flash floods are common in some parts of the sub-region, especially over the arid and semi arid zones even during the seasons with anticipated below normal rainfall conditions.
Pools of warm water have been observed over parts of Indian Ocean; eastern tropical Atlantic Ocean and western equatorial Pacific Ocean. Colder than average SSTs were observed over eastern parts of the equatorial Pacific Ocean and are projected to spread into the rest of the equatorial Pacific Ocean developing into mild La Niña conditions during the forecast period.
The outlook is relevant only for seasonal time scales and relatively large areas. Local and month-to-month variations may occur. Regular forecast updates will be provided by the National Meteorological and Hydrological Services (NMHSs) and the IGAD Climate Prediction and Applications Centre (ICPAC). The users are therefore strongly advised to keep in contact with their respective National Meteorological and Hydrological Services for interpretation of this outlook, finer details, updates and guidance.
The Climate Outlook Forum
From 5 to 6 September 2007, the Twentieth Greater Horn of Africa Climate Outlook Forum (GHACOF 20) was convened in Nairobi, Kenya by ICPAC in collaboration with the National Meteorological and Hydrological Services (NMHSs) and partners to formulate consensus climate outlook for the September to December 2007 rainfall season over the Greater Horn of Africa (GHA). The forum reviewed the state of the global climate system and its implications on the seasonal climate of the sub-region. Among the principal factors taken into account were the observed and predicted SSTs in the tropical Pacific Ocean and over much of the tropical Atlantic and Indian Oceans. Users from Agriculture and food security, disaster management, health, livestock, water resources and media among other sectors were active participants in the forum. The users formulated the potential implications of the outlook for the September to December 2007 season and developed mitigation strategies for the respective countries and sectors.
Methodology
The forum examined the current and expected SST anomalies over the Pacific Ocean as well as the Indian and Atlantic Oceans together with other factors that affect the climate of the sub-region. These factors were assessed using coupled ocean-atmosphere and Regional Dynamical Climate models as well as empirical statistical models and expert interpretation. The current capability of seasonal to inter-annual forecasting allows prediction of spatial and temporal averages and may not fully account for the physical and dynamical factors that influence regional and national climate variability.
The experts established probability distributions to indicate the likelihood of above-, near-, or below-normal rainfall for each zone (see Map). Above-normal rainfall is defined as within the wettest third of recorded rainfall amounts in each zone; near-normal is defined as the third of the recorded rainfall amounts centred around the climatological median; below-normal rainfall is defined as within the driest third of the rainfall amounts. Climatology refers to a situation where any of the three categories have equal chances of occurring.
Outlook
September to December constitutes an important rainfall season over much of the Greater Horn of Africa sub-region. The rainfall outlook for each zone within this sub-region is given below.
Greater Horn of Africa Consensus Climate Outlook for September to December 2007
Zone I: Climatology is indicated over northern Sudan.
Zone II: Increased likelihood of near normal to below-normal rainfall over central and northeastern Sudan; northwestern Ethiopia; and much of Eritrea.
Zone III: Increased likelihood of near normal to below normal rainfall over western Rwanda and northern Burundi.
Zone IV: Increased likelihood of near normal to above normal rainfall over southern Sudan; western, central and parts of northern Ethiopia; extreme northwestern Somalia; northwestern and southwestern Kenya; much of Uganda; central and eastern Rwanda; central and southern Burundi; as well as northern and western Tanzania.
Zone V: Climatology is indicated over northeastern Ethiopia; southeastern Eritrea and much of Djibouti.
Zone VI: Increased likelihood of near normal to below normal rainfall over eastern Djibouti.
Zone VII: Increased likelihood of near normal to below normal rainfall over much of Somalia; eastern and southern Ethiopia; much of Kenya; eastern Uganda; as well as eastern and central Tanzania.
Note:
The numbers for each zone indicate the probabilities (chances of occurrence) of rainfall in each of the three categories: above-, near-, and below normal. The top number indicates the probability of rainfall occurring in the above-normal category; the middle number is for the near normal and the bottom number for the below-normal category. For example, in case of western Rwanda and northern Burundi (zone III), there is 20% probability of rainfall occurring in the above normal category; 45% probability of rainfall occurring in the near-normal category; and 35% probability of rainfall occurring in the below normal category. It is emphasized that boundaries between zones should be considered as transition areas
Contributors
Contributors to this consensus climate outlook included representatives of the Meteorological Services from ten GHA countries (Insititut Geographique du Burundi; Meteorologie Nationale de Djibouti; Eritrea Meteorological Services; National Meteorological Services Agency of Ethiopia; Kenya Meteorological Department; Rwanda Meteorological Service; Sudan Meteorological Authority; Tanzania Meteorological Agency and Uganda Department of Meteorology) and climate scientists and other experts from national, regional and international institutions and organisations such as ICPAC; International Research Institute for Climate and Society (IRI); WMO; ECMWF; UK Met Office; Météo-France; and University of Nairobi. Additional inputs were provided by the National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC); and ACMAD.
