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Climate variability and impact in ASSAR’s East African region

This new paper from ASSAR's east Africa team looks at impact climate-related risks, impacts and vulnerability across the semi-arid regions of East Africa.
Paper cover


Rural livelihoods within East Africa depend on rain-fed agricultural systems and fragile natural resources. Geographically, Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, South Sudan, Uganda, and Tanzania are grouped as East and Horn of African countries. Agriculture in these countries is characterized by smallholder contributions to agricultural production of up to 90% accounting for about 40% of national gross domestic product. About 60% of the total land area in the region is classified as dryland, characterized by an arid and semi-arid climate receiving less than 500 mm mean annual rainfall.

Climate variability in East Africa is related to the complex topography, latitudinal location and effects from regional and global atmospheric circulation. Rainfall and temperature are the two most important climatic variables that display high levels of variability across a range of spatial and temporal scales, and exert significant impacts on human livelihoods, socioeconomic development and ecosystems of East and Horn of Africa. Climate-related shocks such as droughts and floods are not only common, but are also increasing environmental risks in East Africa.

The objective of this working paper* is to review the available information and literature on the current and future climate variability, risks and vulnerabilities across East Africa, and reflect on possible implications for climate adaptation planning and intervention. This paper assessed major climate elements (rainfall and temperature) variability and trends with emphasis on extreme rainfall variability, drought and flood events, which are the major climate related risks in the region. The paper also deals with environmental and socioeconomic vulnerability and the implications for climate related disaster risk management and climate change adaptation planning efforts in the region.

*Download the full paper from the right-hand column.

Methods and Tools (overview)

This working paper was conducted as part of a series of Regional Diagnostic Studies (RDS) undertaken by the Adaptation at Scale in Semi-Arid Region (ASSAR) research project to provide more detailed information on climate variability and related risks over East Africa. The main sources of data for this working paper were academic and grey literature focused on rainfall and temperature variability, drought and flood events, risks and vulnerability issues for East and Horn of Africa. The literature collected predominantly focused on three Eastern Africa countries (namely Kenya, Uganda and Ethiopia). Some articles referring to other parts of eastern Africa (e.g. South Sudan, Somalia, and Tanzania) or other parts of sub-Saharan Africa were also reviewed. The review also drew on broader articles related to the themes of climate change, vulnerability and development that do not have a regional focus.

Although the authors collected literature from various published, peer and non-peer reviewed and unpublished sources, emphasis was given to articles published in peer-reviewed scientific journals. Additional searches were also conducted on broader themes of East Africa’s climate characteristics, climate (temperature and rainfall) variability and drivers, drought and flood incidents, and climate related risks and vulnerability.

Key messages

  • East and Horn of Africa are characterized by great climatological and weather diversity and variability as caused by the complex topography, latitudinal location and effects from regional and global atmospheric circulation.
  • Rainfall and temperature are the two most important climate elements displaying high levels of variability across a range of spatial and temporal scales in East and Horn of Africa, and create diverse ecological and livelihood zones.
  • Rainfall variability is more significant than temperature over the region in terms of impacts and risks.
  • Due to the complex nature of East and Horn of African climate, most of such impacts are felt at local and regional levels.
  • There is a need for a range of spatial and temporal scales of climate management plans and intervention activities.
    • To do this requires clear understanding and modelling of spatio-temporal dynamics of East and Horn of African temperature and rainfall variability.
    • A poor understanding of climate science in the region is attributed to poor data quality and quantity, limited professionals and financial and other research resources.
    • It is important to note that to understand the complex East and Horn of African climate in a way suitable for climate management purposes at different spatial and temporal scales one should first address the indicated gaps in climate science in the region.
  • East and Horn of African countries and other development partners working on the regional climate modeling, climate prediction and climate related disaster management activities should give much emphasis to enhance climate information for policy makers and development planners in the region.
  • Special emphasis should be given to climate data generation/observation/modeling and model development that will enable us to understand, predict and tackle major climate related disasters and risks (drought, erratic rainfall, flood, etc.) that are well known in the region.
  • To datem very little has been done to understand or quantify and model the economic and social effects of climate variability or extremes, at scales beyond the household and village level. This is an area for furture work.

Key findings

Temperature variability

  • East Africa experiences complex temperature conditions due to the effects of its varying topography. Temperature in the region ranges from very hot (>40°C) at the Afar depression, Ethiopia to very cold at the peak of Mount Kilimanjaro.
    • In Ethiopia, the mean annual temperature varies between less than 10°C over the Northwest, Central and Southeast highlands to about 40°C in the lowlands of Afar, eastern and southeastern regions.
    • In Kenya the central highland regions are substantially cooler than the coast, with the coolest (highest altitude) regions at 15°C compared with 29°C at the coast.
  • This variation in temperature conditions across East and Horn of Africa determines evaporation and hence available soil moisture at any point of the region. This has created many vegetation types, fauna and agroecological zones across the region.
  • There is year-to-year variation of the annual maximum and minimum temperatures in the region and evidence of increasing changes in extreme temperature events such as extreme maximum temperature, warm days, warm nights and the duration of warm spells across the region. The greatest increases were observed in central regions, particularly in South Sudan where increases in the March to August period have exceeded 3°C.

Rainfall variability

  • Complex topography and effects from regional and global sea surface temperatures (SSTs) result in significant spatial and temporal rainfall variability over East and Horn of Africa. This has important ramifications for food crops and thus impacts on human livelihoods, food security, water availability and environmental resources.
  • Rainfall over the region shows major spatial variability in its amount, seasonality and year-to-year variation. It is also characterized by significant inter-annual and inter-decadal variability attributed to sea surface temperature (SST) anomalies.
  • the dominant sources of inter-annual and inter-decadal rainfall variability across East and Horn of Africa are the ENSO (El Niño and La Niña) events over the equatorial east Pacific and SST anomalies over Indian Ocean. The periodic circulation of ENSO and its impact on SSTs has been linked to most of the rainfall variability over East and Horn of Africa and the impacts vary in different seasons and regions.
  • Rainfall trends over the past 50 years are less evident than for temperature, and there are large variations in the direction and magnitude of changes across the region. An increase in rainfall in some locations for some seasons is observed but a decrease in rainfall is observed in other parts of the regions and overall trends are weak and hard to detect.
  • At present there is insufficient evidence about the future rainfall shift from climate model projections for East Africa region, due to the presence of challenges for simulating and projecting rainfall variability.


  • Climate variability over the last few decades resulted in frequent drought hazards over East African countries.
  • Principal causes of drought events over East Africa are associated with ENSO-South Oscillation climate variability and SST anomalies over the Indian Ocean.
  • Empirical studies confirm that the frequency, geographical coverage and magnitude of drought hazards increase in the second half of the 20th Century across the East African region. For example, in Kenya the drought frequency increased from once in every 10 years in the 1970s to once in every 5 years in the 1980s, once in every 2-3 years in the 1990s and every year since 2000. Similarly, in Ethiopia, the prevalence of drought increased from once per decade between the1950s and 1980s to once every three years in the 1990s and 2000s.
  • Climate change scenarios show that droughts will become more frequent and severe over the arid and semi-arid parts of the region, where there is chronic water shortage and high temperatures.


  • Flooding is a growing environmental and socioeconomic problem in East Africa, particularly within lowland regions where it can take the form of flash floods or riverine floods resulting from rainfall in highland areas.
  • In Ethiopia, flood hazards are most associated with major river basins: Awash, Wabesheble, Genale and Omo-Ghibe Rivers.
  • In Kenya, floods are the most common climatic disaster, and with a prevalence rate of 27% per year. Flooding affects low lying areas of the country within the five drainage basins of the Lake Victoria Basin. By and large, most floods in Kenya occur immediately after droughts causing devastating impacts.
  • The prevalence and impact of flood hazards show increasing trends over East and Horn of Africa.

Impacts of climate variability

  • There are many climatic, environmental and socio-economic indicators highlighting the high vulnerability of the East and Horn African region to current and future climate variability. One of the most significant is the sensitivity of human livelihoods and economic systems. In East and Horn of Africa the link between climate and livelihood is very strong since the majority of communities depend on rain-fed agriculture and other natural resource based livelihoods.
  • Climate variability, mainly of rainfall (e.g. drought, flood, erratic rainfall and change in rainfall season), has caused significant damage and created challenges for agricultural production and water resources, which leads to scarcity of food, water and other environmental resources for human consumption.
  • East and Horn of African countries are particularly vulnerable to repeated occurrence of drought and flood hazards, expansion of drylands and intensified climate-sensitive diseases.
  • The prevalence of droughts caused major economic and humanitarian impacts during the last four to five decades by severely affecting rain-fed agriculture and pastoralism, which is the backbone of East and Horn of Africa economies.
  • Climate model projections over East and Horn of Africa show warming in all four seasons across the region and a wide range of rainfall patterns, with no clear direction of change. This high level of uncertainty in the future behaviour of rainfall is a significant challenge to understanding and acting upon the risks posed by climate change, and is therefore another source of vulnerability to East and Horn of African countries since there are difficulties planning with high uncertainty.
  • Another issue of vulnerability in East and Horn of Africa is the risk of conflicts on communal land resources. Studies have indicated that climate variability is likely to heighten the risk of communal conflict in the arid and semi-arid areas of East Africa. In particular, erratic rainfall, which reduces the availability of water and pastureland, could be sources of conflicts between pastoral communities and the problem will be stronger in the presence of economic and political marginalization.
  • There is also evidence that climate variability, particularly drought and flooding have caused massive human displacement and migration in Ethiopia. People have migrated from drought and flood affected areas to safer regions by traveling short or long distances.

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