Environmental Sciences Group

Impact of Climate Change on Hydrological Resources in East Africa: A Review ofLiterature Emphasizing on Precipitation.

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Full Title: Impact of Climate Change on Hydrological Resources in East Africa: A Review ofLiterature Emphasizing on Precipitation.

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Corresponding Author: Bantwale Diress Enyew, MSc.National Central UniversityTaipei, TAIWAN

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Corresponding Author's Institution: National Central University

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First Author: Bantwale Diress Enyew, MSc.

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Geoffrey Ogutu, MSc.

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Manuscript Region of Origin: ETHIOPIA

Abstract: Climate change is real and observations show that there are changes in temperatureand precipitation. Surface average temperature is increasing, changes in precipitationare variable from region to region, and may include changes in amount, intensity,frequency, and type of precipitation. This paper reviews the effects or impacts ofclimate on hydrological resources in East Africa (the so called Great Horn of Africa),which, like other regions on the African continent is highly vulnerable to climate changedue its low adaptive capacity, and exposure to other stresses that may not be climatechange related. Whereas warming trends have been observed and projected over theregion under study, precipitation trends and projections are variable, while some areasare projected to have an increase in precipitation, others will have a reduction, echoingthe challenges in precipitation projections for the region. Ensemble climate models arefound to be in agreement with the projected variability in precipitation, and its extremes,even though the models are found to have systematic errors in and around Africa.Analysis of extremes further show an increase on the number of reported hydro-meteorological disasters from average of less than 3 events per year in 1980s to 10events per year in the years 2000-2006. Analysis of the impacts of these changes onhydrological resources indicates an increase in river flows in the early years ofprojections and reduction towards the end of the century. Lake levels over the areasare found to be reducing even with the projected increase in precipitation. This isexpected to reduce hydroelectric power generation capacity, from which the bulk ofelectric power for the region is obtained. The variability and extremes in rainfall is againfound to affect agricultural production and hence will impede economic and humangrowth of the whole region.

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Impact of Climate Change on Hydrological Resources in East Africa: A Review of

Literature Emphasizing on Precipitation.

Bantwale Diress Enyew 1

and Geofferey Ogutu 2

1Nat. Central Univ. & Academia Sinica, Research Center for Environmental ChangeTaipei Taiwan

2Earth System Science group, Wageningen University, Wageningen The Netherlands

Summary: Climate change is real and observations show that there are changes in temperature and

precipitation. Surface temperature is increasing, changes in precipitation are variable from region

to region, and may include changes in amount, intensity, frequency, and type of precipitation. This

paper reviews the effects or impacts of climate on hydrological resources in East Africa (the so

called Great Horn of Africa), which, like other regions on the African continent is highly vulnerable

to climate change due its low adaptive capacity, and exposure to other stresses that may not be

climate change related. Whereas warming trends have been observed and projected over the region

under study, precipitation trends and projections are variable, while some areas are projected to

have an increase in precipitation, others will have a reduction, echoing the challenges in

precipitation projections for the region. Ensemble climate models are found to be in agreement with

the projected variability in precipitation, and its extremes, even though the models are found to

have systematic errors in and around Africa. Analysis of extremes further show an increase on the

number of reported hydro-meteorological disasters from average of less than 3 events per year in

1980s to 10 events per year in the years 2000-2006. Analysis of the impacts of these changes on

hydrological resources indicates an increase in river flows in the early years of projections and

reduction towards the end of the century. Lake levels over the areas are found to be reducing even

with the projected increase in precipitation. This is expected to reduce hydroelectric power

generation capacity, from which the bulk of electric power for the region is obtained. The variability

and extremes in rainfall is again found to affect agricultural production and hence will impede

economic and human growth of the whole region.

ManuscriptClick here to download Manuscript: Climate Change.docx

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1. INTRODUCTION

The earth's global mean climate is driven by incoming energy from the sun and by properties of the sun

and its atmosphere, namely the reflection, absorption and emission of energy within the atmosphere

and at the surface. Changes have occurred in several aspects of the atmosphere, and the surface, which

alter the global energy budget of the earth and therefore cause climate change. Among these are

increases in greenhouse gas concentrations (GHGs).

The change is real and is happening with surface temperatures having increased by about 0.74°C from

1906 to 2005. Observations show that there are changes in precipitation, occurring in the amount,

intensity, frequency and type of precipitation, as a result of direct influences of climate change. These

changes exhibit large natural variability with the oceans and atmospheric circulation patterns having a

significant influence. The impacts of these changes are already affecting ecosystems, biodiversity,

humans and their economic activities.

In both the developed and developing world, climate impacts are reverberating through the economy,

from threatening water availability, hydro-power generation, extreme weather impacts, seal level rise

amongst others (WWF, 2006). In some countries, the change affects services on which large

populations and economies depend upon threatening development and economic stability. These

impacts are expected to worsen as the temperature continues to rise and as precipitation becomes more

unpredictable.

One region of the world bearing the greatest impacts of climate change is the underdeveloped and poor

countries that are most vulnerable (IPCC, 2007); East Africa/N-East Africa is amongst the most

vulnerable regions to climate change impacts since economic growth in these countries are weather

dependent, ranging from rain fed agriculture, to pastoral activities. According to a UNDP report,

agriculture account for around 60% of overall employment in some countries and more than 50% of

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GDP (Africaviewpoint, 2009). The negative impacts are further compounded by many factors

including widespread poverty, human diseases and high population, expected to double the demand for

food, water, livestock forage within the next 30 years.( Davidson et al. 2003, quoted in (Filho(ed)

2011).

Due to a combination of all these factors, climate change is also expected to impede human

development and with more than three countries in this region ranked amongst the lowest in human

development index (UNDP), the issue of climate change and projected changes should be included in

each country’s development agenda. It is therefore necessary to know for this region, the projected

changes in precipitation so as to be included in developing policies for the region’s development

agenda.

1.1 Study area

The area chosen for this study encompasses East African countries of Kenya, part of Uganda, and

Ethiopia, Eritrea, Djibouti; the so called Great Horn of Africa. The Area chosen encompasses latitudes

7S to 15N, Longitude 32E to 50 E, a population of more than 160 million with a majority of the

population living in rural areas and largely dependent on agriculture for their welfare. The area is

characterized by different topographic features resulting in different microclimates, different rainfall

regimes, with some areas having a bimodal pattern while others unimodal. For example, Kenya and

Uganda area have bimodal rainfall patterns (long rains (MAM) and short rains (SOND), Western part

of the great horn (June-September), Central and most of eastern part (June-September (main rainfall

season), Feb-May (season), in South/S-E Ethiopia; two rainy seasons- March-June and September-

November.

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Figure.1 showing a map of the great horn of Africa

1.2 Problem description

The climate effects for Africa and change in precipitation are very different from region to region,

while some areas will become drier, others will become wetter and some countries may derive

economic benefits while others will be adversely affected. This may be compounded by other factors

not related to climate change such as poverty levels and lack of adaptive capacities. Factors such as

climate variability, soil characteristics, water availability and animal health affect the productivity of

land and livestock and a have a large impact on the welfare of the population. Fluctuations in these

factors contribute to year to year changes in levels of poverty, food security and even economic growth

(IGAD, 2007).The bulk of energy supply is based in hydro-power generation.

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Local and regional changes in the character of precipitation also depend on the atmospheric circulations,

which are in turn associated to climate change. For example, rainfall in east Africa is associated to the

shift of the intra- tropical convergence zone (ITCZ), it largely influenced by El Nino (ENSO Index),

Indian Ocean Dipole in during some seasons (IOD), factors that are also influenced by chances in sea

surface temperatures (SSTs).

According to IPCC 4AR, by 2020, between 75 Million and 250 million people are projected to be

exposed to increased water stress due to climate change. Agricultural production is projected to be

severely compromised by climate variability and change, local food supply are projected to be

negatively affected. There is however a knowledge gap on the impacts of climate change in the region,

model studies and observations suggest a Tele-connection between SSTs (esp. mid-latitude pacific

SSTs) and rainfall, via influence on the North-South shift of ITCZ.

The changes in precipitation in this region will have adverse impacts on multiple sectors, but still with

the Global Climate Models (GCM) simulations and projections, the awareness of the expected changes

in precipitation is still not taken into consideration by the governments in this region while crafting

their development strategies and plans.

It is important to identify the 21st century projected changes is precipitation for the greater horn of

Africa so that policy makers are able to incorporate the projections in their economic planning. Further,

there has been an increase in the number of reported hydro meteorological disasters in the region, from

an average of less than 3 events/year in the 1980s, to over 7 events /year in the 90s, and almost 10

events per year between 2000-2006, these hydro meteorological disasters affected on average almost

two million people per year (Shongwe et al. 2010), hence even more need to understand the changes in

climate. This review paper seeks to highlight the projected changes in precipitation in the region,

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comment on the uncertainties in the projections, reiterate the probable impacts of the changes on

different sectors.

2.0 Past, present, and future projections of precipitation trends in East Africa.

2.1 Current precipitation trends

Research from recent decades suggests that Eastern Africa has been experiencing an intensifying dipole

rainfall pattern on a decadal timescale. The dipole is characterized by increasing rainfall over the

northern sector and declining amounts over the southern sector (Schreck and Semazzi 2003). Also, the

region has suffered both excessive and deficient rainfall in recent years (Hastenrath et al., 2007) and in

particular, the frequency of anomalously strong rainfall causing floods has increased.

The increase in rainfall in East Africa, extending into the Horn of Africa, is also robust across the

ensemble of models, with 18 of 21 models projecting an increase in the core of this region, east of the

Great Lakes. This East African increase is also evident in Hulme et al. (2001) and Ruosteenoja et al.

(2003) (as cited in IPCC 2007). This is shown in figure 2 depicting the annual mean. DJF and JJA

fractional change of precipitation between periods 1980-1999, 2080-2099 and 2099 averaged over 21

models.

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Figure 2. Annual mean, DJF and JJA fractional change in precipitation between 1980 to 1999 and

2080 to 2099, averaged over 21 models

2.2 Projection

All of Africa is expected to warm this century with different projections for annual precipitation for

different regions of the continent. There is likely to be an increase in annual mean rainfall in East

Africa. The MMD are however noted to have significant systematic errors in and around Africa making

it difficult to assess the consequences for climate projections, for example, excessive rainfall in the

south, southward displacement of the Atlantic Inter-Tropical Convergence Zone (ITCZ), insufficient

upwelling off the west coast. There exist biases in simulation of African climate across the MMD

models, these biases are systematic with 90% of the models overestimating precipitation in southern

Africa by more than 20% on average and in some cases in as much as 80% over a wide area often

extending into equatorial Africa. Despite these deficiencies however, AGCMs can simulate the basic

pattern of rainfall trends in the second half of the 20th

century if given the observed SST evolution as as

boundary conditions. Also notable is that there is less confidence in the ability of AOGCMs to generate

inter annual variability in the SSTs of the type known to affect African rainfall, as evidenced by the

fact that very few AOGCMs produce droughts comparable in magnitude to the Sahel drought of the

1970s and 1980s, with exceptions that are yet understood (Hoerling et al., (2006) also cited in IPCC

2007)

2.3 Extremes

Research on changes in extremes specific to Africa are limited, however, a general increase in the

intensity of high-rainfall events, associated in part with the increase in atmospheric water vapor is

expected.

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The countries in East Africa are frequently exposed to climate extremes such as drought and flooding.

Recent research suggests that warming sea surface temperatures, especially in the southwest Indian

Ocean, in addition to inter-annual climate variability (i.e., El Nino/Southern Oscillation) may play a

key role in East African rainfall and may be linked to the change in rainfall across some parts of

equatorial and subtropical East Africa (Cane et al., 1986; Plisnier et al., 2000; Rowe, 2001). Warm sea

surface temperatures are thought to be responsible for the recent droughts in equatorial and subtropical

Eastern Africa during the 1980s to the 2000s (Funk et al., 2005).

An analysis of data from the International disaster Database (EM-DAT), Shongwe et al. (2009) found

that there has been an increase in the number of reported hydro meteorological disasters in the region

from an average of less than 3 events per year in the 1980s to over 7 events per year in the 1990s, and

10 events per year from 2000 to 2006, with a particular increase in floods. In the period 2000-2006

these disasters affected on average almost two million people per year.

2.4 Variability

Sylla et.al (2009) used the latest version of the ICTP regional climate model, RegCM3 of relevant

features of African climate, including key circulation systems, surface air temperature and precipitation,

over different areas of the domain. Double-rainy season structure is marked over the Horn of Africa (as

shown in figure 3) with the two rainy seasons occurring in April–May and October–December and

being separated by a very dry season in June–September. This double-peaked structure is associated

with a north–south migration of the ICTZ that sweeps this and adjacent equatorial regions.

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Figure 3. Annual cycle of Precipitation (in mm/day) from RegCM (green). GPCP (black solid), FEWS

(dotted), CRU (dashed) and ERAIKM (blue) for Horn of Africa.

3.0 Impact on hydrological resources

Climate change is expected to impact negatively on most African countries given the poverty levels

and lack of adaptive capacities. The changes may be far reaching as to compromise economic

development and wellbeing of the population in these regions given that most of the economies of

countries in East Africa are highly dependent on agriculture, which in turn depend on climatic factors

such as rainfall. Despite this dependency of development on economic development, climate change

remains unrecognized in many African countries. And yet, the impacts of climate change are not just of

environmental concern, but will impede efforts to tackle poverty and promote national development.

Moreover, the problems impeding socio-economic development in African countries are often the same

as those that increase vulnerability to climate change (Orindi and Murray, 2005).

Further, climate change and variability has a potential impact in Africa in general and East Africa in

particular in different natural resources such as water availability, which in turn greatly influence

Agriculture, energy, ecosystem and many other sectors. Even in the absence of climate change, the

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present population trends and patterns of water use indicate that more Africa countries will exceed the

limits of their economically usable, land-based water resources before 2025 (IPCC, 2207)

The following section seeks to give highlights of the impacts of climate (precipitation) change on

hydrological resources in east Africa.

3.1 Water availability and water quality

One of the most widespread and potentially devastating impacts of climate change in East Africa will

be changes in the frequency, intensity, and predictability of precipitation. This will in turn affect water

availability and quality. Projections of climate change suggest that East Africa will receive increased

rainfall and increased occurrence of rainfall extremes. Increased precipitation during already wet

periods may cause flooding and erosion and may complicate water management issues. Less

precipitation expected during the already dry seasons may cause frequent and severe droughts and

increased desertification (Case, 2006).

Impact assessment of climate change on water resource using six models in Africa shows non

uniformity across the continent. The result shows a likely increase in number of people who could

experience water stress by 2055 in northern and southern Africa and more people in eastern and

western Africa will be likely to experience a reduction rather than an increase in water stress IPCC

2007).

The Water sector is considered as to be very sensitive to climate changes. In East African lakes, deep

water temperatures have risen by 0.2 to 0.70C since the early 1900s (IPCC, 2007). Inter-annual lake

level fluctuations and lake-level volatility have been observed in East African lakes since the 1960s,

probably due to periods of intense drought followed by increases in rainfall and extreme rainfall events

in late 1997 (Riebeek, 2006). These heavy rains have been possibly attributed to large scale

atmosphere-ocean interactions in the Indian Ocean. Funk et al. also clearly link drops of East African

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lakes to ENSO- events. It is also stated that “following a large ENSO related jump in 1998, levels in

Lake Tanganyika, Victoria and Turkana have been dropping. Lake Tana, on the other hand shows little

trend, except perhaps for a recent drop in 2002-04. East Africa lakes elevation data from the Global

Reservoir and lake Elevation database obtained from Jason-1, TOPEX/Poseidan Satellite experiment

also show a reduction in lake levels over the entire region. See figure 4

Figure 4. Showing lake levels in Eastern Africa (Imagery obtained from USDA PECAD crop

explorer:www.pecad.fas.usda.gov/cropecplorer/global_reservoir)

Taye et.al (2010), investigated the impact of climate change on hydrology and hydrological extreme on

Nyando and Lake Tana catchment in the region of the Nile Basin catchment by employing 17 different

General circulation models (GCMs) simulation under two future emission scenarios of A1B and B1 for

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the 2050s. Their results reveal that the hydrological models projected extreme peak flow of river

Nyando until the 2050 general trend to increase and the projected changes in low flows show both

increase and decreases of the flow values from the control period (1971-1990).

While unclear trend is observed for Lake Tana catchment for cumulative volumes as well as high and

low flows .The period 1990–2000 (11years) was used as baseline control period to run the hydrological

models in this catchment. The projected change in annual mean flow using four GCMs for both

catchments is as shown in figure 5. This result illustrates that for the 2050s the flow in Nyando

catchment will likely increase more than for the outflow of Lake Tana catchment, the impact

differences between A1B and B1 emission 20 scenarios are also shown.

Figure 5. Regional projected change comparison of mean annual flow volumes between

Nyando and Lake Tana catchments for eight GCM runs.

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3.2 Consequences for different sectors

3.2.1 Agriculture

According to the U.N. Food and Agriculture Organization (FAO, 2004), the number of African

food crises per year has tripled from the 1980s to 2000s. Droughts have diminished water supplies,

reduced crop productivity, and have resulted in widespread famine in East Africa. Most of rural

poor in Sub-Saharan Africa rely, for their livelihoods and food security, on highly sensitive rain fed,

small-scale, subsistence farming, pastoral herding and direct harvesting of natural services of

ecosystem which are vulnerable to climate-related stress; such as change in temperature,

precipitation, and increase in frequency of droughts and floods. Under both the A1 and B1

scenarios, mixed rain-fed semi-arid systems are shown to be affected in the Sahel, as well as mixed

rain-fed and highland perennial systems in the Great Lakes region and in other parts of East Africa

(IPCC 2007). Figure 6 shows the agricultural areas with livestock only systems(LGA) and rain-fed

mixed crop/livestock systems(MRA) projected by HadCM3 GCM to undergo more than 20%

reduction in length of growing period by 2050 for the A1 and B1 scenarios.

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Figure 6. Agricultural areas within the livestock-only systems (LGA) in arid and semi-arid areas,

and rain-fed mixed crop/livestock systems (MRA) in semi-arid areas, are projected by the HadCM3

GCM to undergo >20% reduction in length of growing period to 2050, SRES A1 (left) and B1

(right) emissions scenarios, after Thornton et al. (2006).

Deressa and Hassan (2009) assess the economic impact of climate change on Ethiopian farmers, using

the Ricardian approach to inform policy makers on proper adaptation options to counteract the harmful

effects of such change and made an attempt to predict the extent to which projected climate changes

will affect net revenue from crop farming in Ethiopia. Deressa et.al (2009) analysed samples of 1000

farmers from different Agro-ecological regions to estimate the net revenue using seasonal climate

means for summer, fall, spring and winter. They indicated that, the marginal analysis of an

infinitesimal change in temperature and precipitation during winter and summer seasons significantly

reduce the net revenue per hectare. Increasing in temperature marginally during winter and summer

season reduces the net revenue per hectare by US$997.7 and US$ 177.6 respectively. Increasing

temperature marginally during the spring and fall seasons increase the net revenue per hectare by

US$ 337.8 and US1879.7 respectively. Increasing precipitation during the spring season increase net

revenue per hectare by US$225.1 and increasing precipitation levels during the winter significantly

reduces the net revenue per hectare by US$464.7.

Jing-Yun you and Ringler (2010) modelled the hydro-economic impact of climate change in Ethiopia.

This study integrates climate change models for water stress, flood impacts, and CO2 fertilization

effects into an economy wide, multi-sector, and multiregional model of the Ethiopian economy.

They analysed the impact of climate change on the net revenue per hectare using uniformly changed

temperature and precipitation. These scenarios increase temperature by 2.50C and 5

0C and reduce

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precipitation by 7% and 14%. Increasing temperature by 2.50C and 50C affects net revenue per

hectare marginally. Moreover, reducing precipitation by 7% and 14% also reduces net revenue per

hectare even though the level of damage is very small. Predicted values of temperature and rainfall

from three climate change models (CGM2, HaDCM3 and PCM) were also applied to help understand

the likely impact of climate change on Ethiopian agriculture. All the models forecast increasing

temperature levels for the years 2050 and 2100. With respect to precipitation, the years 2050 and 2100

both HaDCM3 and PCM predicted increasing precipitation over these years. Using climate forecasts

from all the models the study revealed that by 2050 net revenue per hectare would increase whereas by

2100 it would decrease.

Jing-Yun et.al (2010) analysed precipitation from the selected AOGCMs confirmed that the statement

from IPCC AR4, which states, there is likely to be an increase in annual mean rainfall in East Africa.

The change in average annual precipitation between the study period (2003-2050) and the base period

(1971–2000) in Ethiopia shows SRES A2 has the highest degree of change, at 6%, and SRES B1 has

the lowest, at 1.26%. The change in the moderate case, SRES A1B, is between these values, at around

5%. In addition to the amount of precipitation, incremental variability of precipitation is also examined.

The standard deviation calculated from the AOGCMs also increases during the study period. Therefore,

Ethiopia is likely to face more fluctuating rainfall, which will affect the stable water supply for crop

cultivation and also increase the possibility of flooding.

The average GDP growth under the different scenarios with the Water Sector Development Plan

(WSDP) irrigation program. The irrigation program could enhance the positive influence and reduce

the negative impact of climate change. With the WSDP, GDP projections are US$54.7 billion, US$50.2

billion, and US$56.2 billion for SRES A1B, A2, and B1, respectively. Compared to the GDP projection

of the base scenario, US$82.2 billion, the losses due to climate change are between US$27 billion and

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US$32 billion—around 3% of GDP. GDP projections without the WSDP are US$44.4 billion, US$40.3

billion, and US$45.8 billion, respectively, for SRES A1B, A2, and B1. The losses are also between

US$28 billion and US$32 billion—around 40% of the base scenario’s GDP, US$72.8 billion—a little

higher than when the WSDP is applied.

For Ethiopian context, the results show that climate change especially increasing temperature is

damaging the Ethiopian government must consider designing and implementing adaptation policies to

counteract the harmful impact of climate change. Adaptation options include investment in

technologies such as irrigation, planting drought tolerant and early maturing crop varieties

strengthening institutional set-ups works in resource and education farmers and encouraging ownership

of livestock.

3.2.2 Hydropower

The bulk of electric power in East Africa is obtained from hydro-generation. Any change in

precipitation pattern extremes will affect not only power generation and availability, but also human

settlements in river floodplains. During periods of high rainfall water from the dams will have to be

released, this will cause enormous flooding in settlements downstream and creating problems with

water availability and quality. Power generation will be hampered during periods of drought due to low

water levels in the dams, this may lead to power generation below capacity or even a complete

shutdown of power plants, this will in turn lead to other problems related to the economies of the

countries such as negative economic growth and slow down of the manufacturing sector.

A case in point is the huge energy deficits experienced in Kenya as a result of drought in the year 2000

and led to massive power rationing in which in which industries were supplied with power for only 8

hours during the day, on alternate days for 3 days a week (Nyoike, 2002). After this, there have been

cases of power generation below capacity during periods of drought.

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In assessing the potential impacts of climate change on the hydrology and water resources of the Nile

River Basin using a macro scale hydrology model, and bias corrected and corrected 21st century

simulations from 11 GCMs and two global emission scenarios(A2 and B1) archived from IPCC Fourth

Assessment Report(AR4), Beyena et al. 2010 found out that the Nile river is expected to experience

increase in stream flow early in the study period(2010-2039), due to generally increased precipitation,

and to decline during the mid and late century as a result of both precipitation decline and increased

evaporative demand, see tables 1 and 2.

Table 1. Simulated streamflow by each climate model routed to the main Nile gauging station at High

Aswan Dam for global emission scenarios A2(B1).(numbers expressed as % of the mean annual

historical flow (1950-1999). (Source:Beyene et al.,2010)

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Table 2. Simulated streamflow by each climate model routed to the Blue Nile gauging station at at

Eldiem for global emission scenarios A2(B1).(numbers expressed as % of the eman annual historical

flow(1950-1999). (Source:Beyene et al.,2010)

Further the findings show that under both scenarios in general, the results indicate increasing

precipitation during the early 21st century in the multi-model average resulting into larger basin stream

flow increases due to a multiplier effect on stream flow resulting from temperature increases. In

contrast the, the temperature effects tend to dominate later in the 21st century and are compounded by

precipitation decreases. These findings suggest that the Nile basin is more sensitive to temperature

changes as opposed to precipitation, particularly in the late 21st century. Similar findings were also

found in a study in the Lake Victoria region.

These results show that predicted decreased outflows into the river Nile may greatly hamper generation

of electricity from the Nile waters. With many more power plants planned in this region by both the

Ethiopia and Uganda governments, the expected capacity of these plants may not be achieved in the

later parts of the century.

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4.0 Conclusions

East Africa, like the rest of Africa will be impacted by climate change, the whole region is expected to

warm, and robust findings show that the rise will continue over the whole region. Precipitation trends

are however variable, research show that East Africa has been experiencing intensifying dipole rainfall

pattern on decadal timescales characterized by increasing rainfall on the Northern sector and a decline

in the southern sector.

Increase in rainfall is robust across an ensemble of models with 18 out of 21 models projecting an

increase in the Annual mean, DJF, MAM, SON, and JJA rainfall in the core of the region. An increase

in the number of reported hydro-meteorological disasters in East Africa has increased from an average

of less than 3 events per year in 1980s to 10 events per year from 2000-2006, with particular increase in

floods.

Models used to simulate climate projections are noted to have significant errors in and around Africa

20

hence biases in simulation of African climate across the models. Despite the deficiencies, the AGCMs

can simulate the basic patterns of rainfall trends in the second half of the 20th

century with observed

SSTs as boundary conditions. This is mainly because of less confidence in the ability of AOGCMs to

generate inter-annual variability in the SSTs in of the type known to affect African rainfall.

Impacts analysis show that changes in frequency, intensity, and predictability of precipitation will

affect water availability and quality. Increased precipitation during already wet periods will cause

flooding and erosion complicating water management issues in terms of water supply, quality,

sanitation and infrastructure. Less rain during drier periods will result into droughts, affecting

agricultural production. This may result in less crop yields, famine, malnutrition and other effects.

Under both the A1 and B1 scenarios, mixed rain-fed semi-arid systems are shown to be affected in the

Sahel, as well as mixed rain-fed and highland perennial systems in the Great Lakes region and in other

parts of East Africa

Since agriculture is the mainstay of the population in this region, climate change will affect agricultural

production, be it crop or animal husbandry will result in income losses for the farmers. Marginal

analysis of infinitesimal change in temperature and precipitation show that by 2050, net revenue per

hectare would increase whereas by 2100, it would decrease. Deep water temperatures from east African

lakes have risen by 0.2-0.7 Celsius since early 1900s, a further increase in this will affect fishery

industry.

Lake levels in this area have been declining despite an earlier rise after the 1997-1998 El Nino event,

this is despite an expected rise in levels due to increase in precipitation. The lake levels have been

noted to be correlated with ENSO events. This may be related to or have an influence on the peak river

flows. An analysis of peak river flows are shown to be extreme in the early part of the century up to

1939 and a reduction towards the end of the century.

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Averaged across GCM models for SRES A2 and B1 global emissions scenarios and for periods 2010-

2039 to 2070-2099, multimodal averages suggest that the entire Nile basin, Blue Nile and Lake

Victoria regions will experience increases in DJF rainfall with the exception of the Lake Victoria

region which is expected to experience decreases in the late 21st Century.

The bulk of electricity supply from this region is mainly hydropower; a reduction in lake levels and

projected reduction in river flows are likely to reduce the hydroelectric power potential in this region.

This will further impede economic development and amplify the impacts of climate change in East

Africa.

5.0 Recommendations

Assessment of impact of climate change in a region is essential to quantify the potential future damages

imposed to this region considering mitigation and adaptation options. Nevertheless, there is no

comprehensive region wide impact assessment of climate change on different sectors. There should

therefore be a region wide comprehensive assessment of the potential impact of climate change in East

Africa.

There is varying results of future projections rain fall in East Africa between IPCC reports and some

recent research. Therefore, a detailed study of the assessment of impact of climate change on region is

recommended by employing the RGCMs.

The quality and quantity of research related to impacts of climate change in East Africa are limited

compared to other regions. More research should be conducted on the region for a better assessment of

climate change impacts.

In order to reduce the negative impacts of climate change and enhance positive impacts, East African

governments must invest in technologies such as irrigation, drought tolerant and early maturing crop

22

varieties and even in crops that do well in more rainfall at particular seasons.

More investments in other renewable forms of energy rather in hydro-power should be considered to

mitigate the effects of reduced lake water levels and river flows that otherwise would impede

hydropower generation.

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