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Impacts of climate change on water resources in southern Africa:
A review
Samuel Kusangaya
a,
⇑
, Michele L. Warburton
a
, Emma Archer van Garderen
b
, Graham P.W. Jewitt
a
a
University of KwaZulu Natal, Centre for Water Resources Research, School of Agriculture, Earth and Environmental Sciences, Private Bag X01, Scottsville, Pietermaritzburg 3209,
South Africa
b
Climate Studies, Modeling and Environmental Health, CSIR Natural Resources and Environment, Building 1, Corner Carlow and Rustenburg Roads, Emmarentia 2195, South Africa
article info
Article history:
Available online 2 October 2013
Keywords:
Climate change
Southern Africa
Water resources
Hydrological modelling
Uncertainty
abstract
The Intergovernmental Panel on Climate Change concluded that there is consensus that the increase of
atmospheric greenhouse gases will result in climate change which will cause the sea level to rise,
increased frequency of extreme climatic events including intense storms, heavy rainfall events and
droughts. This will increase the frequency of climate-related hazards, causing loss of life, social disruption
and economic hardships. There is less consensus on the magnitude of change of climatic variables, but
several studies have shown that climate change will impact on the availability and demand for water
resources. In southern Africa, climate change is likely to affect nearly every aspect of human well-being,
from agricultural productivity and energy use to flood control, municipal and industrial water supply to
wildlife management, since the region is characterised by highly spatial and temporally variable rainfall
and, in some cases, scarce water resources. Vulnerability is exacerbated by the region’s low adaptive
capacity, widespread poverty and low technology uptake. This paper reviews the potential impacts of cli-
mate change on water resources in southern Africa. The outcomes of this review include highlighting
studies on detected climate changes particularly focusing on temperature and rainfall. Additionally,
the impacts of climate change are highlighted, and respective studies on hydrological responses to cli-
mate change are examined. The review also discusses the challenges in climate change impact analysis,
which inevitably represents existing research and knowledge gaps. Finally the paper concludes by outlin-
ing possible research areas in the realm of climate change impacts on water resources, particularly
knowledge gaps in uncertainty analysis for both climate change and hydrological modelling.
Ó2013 Elsevier Ltd. All rights reserved.
1. Introduction
The African continent has been identified as particularly vulner-
able to the changing climate due to its envisaged low adaptive
capacity and vulnerability (Callaway, 2004). The southern African
region is regarded as one of the most vulnerable regions in Africa
(IPCC, 2007b). Within the climate change matrix, water resources
are at the epicentre of projected climate change impacts. If the ob-
served changes in climate in the last century (IPCC, 2007a,b) per-
sist into the future, the potential impacts on water resources are
likely to increase in magnitude, diversity and severity. Given the
already large spatial and temporal variability of climatic factors
in southern Africa (Gallego-Ayala and Juízo, 2011); climate change
impacts on water resources are likely to be more pronounced in
the near future than previously foreseen (IPCC, 2007b). Climate
change impacts on water resources will have both direct and indi-
rect effects on the socio-economic and the biophysical environ-
ments (Arnell, 1999; Bates et al., 2008; Kundzewicz et al., 2008;
Rutashobya, 2008; Schulze, 2005a,b). Already, this is evident in
several sectors, such as agriculture (Crane et al., 2011; Pielke
et al., 2007; Vermeulen et al., 2012), health (Bunyavanich et al.,
2003; Gage et al., 2008), ecosystems and biodiversity (Eriksen
and Watson, 2009) and energy generation (Magadza, 1994, 2000;
Yamba et al., 2011).
The assessments of the Intergovernmental Panel on Climate
Change (IPCC, 2007a,b) have demonstrated that, due to increasing
greenhouse gases, the Earth’s climate is changing. Future experi-
ences are likely to include higher sea levels, more intense storms
and heavy rainfall events (McBean and Ajibade, 2009). Climate
hazards are already occurring and impacting human settlements
causing loss of life, social disruption and economic hardships
(Desanker, 2002; Hulme, 1996; IPCC, 2001; McBean and Ajibade,
2009). Such hardships are already being heavily felt by the poor
in most Southern African Development Community (SADC)
1474-7065/$ - see front matter Ó2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.pce.2013.09.014
⇑
Corresponding author. Tel.: +26 3772918174.
E-mail addresses: kusangayas@yahoo.com (S. Kusangaya), WarburtonM@
ukzn.ac.za (M.L. Warburton), earcher@csir.co.za (E. Archer van Garderen), jewittg@
ukzn.ac.za (G.P.W. Jewitt).
Physics and Chemistry of the Earth 67–69 (2014) 47–54
Contents lists available at ScienceDirect
Physics and Chemistry of the Earth
journal homepage: www.elsevier.com/locate/pce
Author's personal copy
countries as reported by Magadza (1994), Ngigi (2009) and Simms
and Reid (2005).
While there are diverse views regarding the magnitude of
change of climatic characteristics in southern Africa, and the possi-
ble impacts at the scale at which land and water resources are
managed, several scholars have however noted that there is cer-
tainty, that, climate change will impact on the availability and
use of water resources (see for example Desanker and Magadza,
2001; Matondo et al., 2005; Ngigi, 2009; Omari, 2010;Schulze,
2000b, 2005a;Yamba et al., 2011).
What is certain is that in southern Africa, our climate is chang-
ing. To date, however there are only few studies examining the
hydrological responses of climate change in Africa (Boko et al.,
2007) and southern Africa (Manase, 2010) in particular, upon
which base generalisations about the future availability of water
resources can be made for planning and management purposes.
There are also a myriad of other supply and demand pressures such
as land degradation, pollution and population and urban growth,
affecting water resources (Arnell, 1999; McMullen, 2009; United
Nations, 2011). Climate change has the potential to exacerbate
these pressures in southern Africa. The region encompasses the fol-
lowing countries: Angola, Botswana, the Democratic Republic of
Congo, Lesotho, Madagascar, Malawi, Mauritius, Mozambique, Na-
mibia, Seychelles, South Africa, Swaziland, Tanzania, Zambia and
Zimbabwe. To our knowledge, there is no comprehensive review
of studies assessing impacts of climate change on water resources
in southern Africa. The objective of this paper is to review litera-
ture on detection of changes in climate and impacts of climate
change on water in southern Africa, as well as identifying and high-
lighting research gaps and needs.
2. Detection of climate change
Long term trend analysis of atmospheric variables such as tem-
perature, rainfall and evapotranspiration have been used exten-
sively [e.g. rainfall by Warburton and Schulze, 2005; Dore
Mohammed, 2005; temperature by Kruger and Shongwe, 2004;
New et al., 2006; Warburton et al., 2005; evaporation (and soil
moisture) by Malisawa and Rautenbach, 2012], as proxies for
detecting changes in climate. The increased frequency of occur-
rence of extreme events such as droughts, floods and cyclone activ-
ity in southern Africa has also been cited as evidence of a changing
climate. Most scientists (e.g. Mirza, 2003; Rosenzweig et al., 2001;
Reason and Keibel, 2004; Reason, 2007; Warburton et al., 2005) are
of the view that the increased frequency of extreme events may be
attributable to increasing greenhouse gas (GHG) emissions. The
following section reviews some of the studies undertaken on cli-
mate change detection particularly on rainfall and temperature.
2.1. Temperature
Analyses of both remote sensing derived and observed temper-
ature records in southern Africa agree that over the last decades
the region has been experiencing a warming trend. Several schol-
ars, including Kruger and Shongwe (2004),Hughes and Balling
(1996),Warburton et al., (2005),Unganai (1996) and New et al.,
(2006) analysed observed temperature trends. The basic conclu-
sion drawn from these studies is that temperatures are rising, with
minimum temperatures rising faster than maximum temperatures.
The overall result has thus been a warming trend.
An increase in temperature typically causes the intensification
of the hydrological cycle, as a result of the increase in evaporation
as well as rainfall (Warburton et al., 2005). That is, temperature
changes may lead to changing patterns of rainfall, the spatial and
temporal distribution of runoff, soil moisture, and groundwater
reserves, as well as (increase) the frequency of occurrence of
droughts and floods (Schulze, 2011). Consequently, temperature
changes have a direct bearing on water resources availability with-
in southern Africa.
Most studies analysing temperature changes were carried out in
South Africa. For example, Kruger and Sekele (2012) concluded
that warm extremes increased and cold extremes decreased for
South Africa. Kruger and Shongwe (2004) concluded that 23 (of
26) stations analysed showed positive trends in annual mean max-
imum temperature, 13 statistically significant, with trends higher
for central stations than those closer to the coast. Levy (1996)
showed an upward trend of 10% (+1.5 °C) noted in the winter ser-
ies. Jones (1994) showed a warming rate of 0.31 °C per decade
whilst Karl et al. (1993) concluded that an increase in both
maximum temperatures and minimum temperatures was ob-
served. Tshiala et al. (2011) in studying catchments in the Limpopo
Province of South Africa showed an increase of 0.12 °C/decade in
the mean annual temperature. However, Mühlenbruch Tegen
(1992) concluded that the data were inconclusive as to whether
South Africa was warming or cooling for the duration of the
study.
On regional and country level studies, Collins (2011) concluded
that significant increasing temperature trends were found in
southern hemisphere of Africa. Morishima and Akasaka (2010) in
studies in southern Africa concluded that annual mean surface
temperature showed an increasing trend across the whole region,
with particularly large rates of increase in Namibia and Angola.
New et al. (2006) analysed daily (maximum and minimum) tem-
perature between 1961 and 2000 for the SADC region and con-
cluded that temperature extremes show patterns consistent with
warming over most of the region with diurnal temperature range
(DTR) showing consistent increases in a zone across Namibia, Bots-
wana, Zambia, and Mozambique, coinciding with more rapid in-
creases in maximum temperature than minimum temperature
extremes. Hulme et al. (2001) concluded that for southern Africa
temperatures during the 1990s were higher than they were earlier
in the century and are currently between 0.2 and 0.3 °C warmer
than the 1961–1990 average.
Overall, for southern Africa we can conclude that temperatures
are rising, with minimum temperatures rising faster than maxi-
mum temperatures for the whole region. As a result there is also
a notable decrease in cold extremes and an increase in warm ex-
tremes. From the temperature studies, apart from the general
trend of increasing temperatures, still unresolved in the magnitude
of change which is variable across the region.
2.2. Rainfall
Climate change detection studies on rainfall that have been car-
ried out to date used observed, interpolated and remote sensing
derived rainfall. For Malawi, Ngongondo et al. (2011), using 42
rainfall stations showed that most stations revealed statistically
non-significant decreasing rainfall trends for annual, seasonal,
monthly and the individual months from March to December at
the 5% significance level. For Zambia, Sichingabula (1998) showed
an increasing 11-year coefficients of variation (CVs) for selected
stations and decreasing rainfall trends observed in southern Zam-
bia after 1975. For Zimbabwe, Mazvimavi (2010) concluded that
rainfall in Zimbabwe has high inter-annual variability, and cur-
rently any change due to global warming is not yet statistically
detectable.
Several studies in South Africa showed that rainfall in South
Africa is characterised by high inter-annual variability. For exam-
ple, Kane (2009) showed that annual rainfall had considerable
year-to-year fluctuations (50–200% of the mean), while 5-year run-
ning means showed long-term fluctuations (75–150% of the mean).
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However, running means over 21 years did not indicate linear
trends. In the largest part of South Africa there was no real evi-
dence of changes in rainfall over the past century Kruger (2006),
there are, however, some identifiable areas where significant
changes in certain characteristics of rainfall have occurred over
the period 1910–2004.
Still other studies have looked at rainfall changes for the southern
African region. For example, Shongwe et al. (2009) concluded that
currently, rainfall trends are characterised by more severe droughts
in the southwest of southern Africa and enhanced rainfall farther
north in Zambia, Malawi, and northern Mozambique. However,
Chamaillé-Jammes et al. (2007) and Joubert et al. (1996) concluded
that rainfall in southern Africa showed no consistent or statistically
significant trends across the region, with; however, a noted decrease
of regionally-averaged total rainfall (but is not statistically signifi-
cant). Nicholson (2000, 2001), found a shift from relatively wet con-
ditions of the 1920–1950s to dry conditions from the 1970s onward.
For the northernmost part of southern Africa, including Zimbabwe,
an increase in rainfall in the 1970s of 6% followed by a reduction of
5% in the 1980s was shown by Nicholson (2001).Morishima and
Akasaka (2010) analysed rainfall data for the 1979–2007 period for
southern Africa and concluded that annual rainfall has decreased
over the African continent from the equator to 20°S, as well as in
Madagascar resulting in a shorter and weaker rain season in south-
ern Africa, with rainfall in Angola, Zambia, and Namibia tending to
decrease from December to March. New et al. (2006) reported a spa-
tially coherent increase in consecutive dry days over much of south-
ern Africa in the last decades of the twentieth century. However,
analysis of observed rainfall trends for Zimbabwe (1933–2000) by
Mazvimavi (2010) showed that there was no statistically significant
rainfall reduction in Zimbabwe. This contrasts sharply, however,
with earlier results from Unganai (1996) who concluded that areal
annual rainfall in Zimbabwe had declined by 10% between 1900
and 1994. Elsewhere, in South Africa, Hewitson and Crane (2005)
using 50 years of data (1950–1999) reported rainfall increases in re-
gions where orography plays a strong role, and also increases in late
summer dry spell duration for much of the summer rainfall region.
These studies and reports suggest that annual rainfall has not had
a clear tendency in the last 20 or 30 years, but most concur that
dry periods in southern Africa have become longer and more intense.
The basic conclusion from the analysis of rainfall trends is that
changes in rainfall are subject to considerable uncertainty, regarding
the extent (spatial and temporal) and magnitude of change (Schulze,
2005a and 2005b; Mazvimavi, 2011). This is largely because rainfall
is characterised by high inter-annual variability over southern Afri-
ca. The insufficient data records for southern Africa also make anal-
ysis challenging (Mazvimavi, 2011). These limitations render
detection of rainfall changes due to climate change difficult. How-
ever, as pointed out by Warburton and Schulze (2005) changes in
rainfall have important implications for the hydrological cycle and
for water resources, as rainfall is the main driver of variability in
the water balance, upon which humans and the environment
depend.
3. Climate change impacts on hydrological response drivers
Manase (2010) reported that most climate change impact stu-
dies have been carried out in developed countries with few studies
undertaken for developing countries, particularly from Africa. Sub-
Saharan Africa is still lagging behind most regions of the world in
general scientific research (Mouton et al., 2010) including climate
change. This dearth of literature on climate change impacts for
sub-Saharan Africa has been attributed to inadequate research fi-
nancing (Yanda, 2011), poor research infrastructure (Manase,
2010), technological constrains (Chhetri et al., 2012), constrained
information dissemination (Mazvimavi, 2011) and a myriad of
other endogenous and exogenous factors. However, it is in sub-Sa-
haran Africa that the impacts of climate change are likely to be se-
verest due to the extreme poverty, hunger and malnutrition
(Magadza, 2010) and low adaptive capacity (Arnell, 1999; Mazvi-
mavi, 2011). Several studies in the region have, however, looked
at the potential impacts of climate change on water resources, with
a general consensus that, as mentioned earlier, climate change will
affect both the quality and quantity of available water resources in
the region (e.g. Mazvimavi, 2008; Schulze, 2000a, 2005a; Schulze
et al., 2010; Warburton et al., 2010). The following section reviews
impacts of climate change on key climatic drivers of hydrological
responses namely: temperature and rainfall in southern Africa.
3.1. Temperature
Changes in temperature and rainfall have a direct effect on the
quantity of evapotranspiration and on both quality and quantity of
the runoff. Consequently, the spatial and temporal availability of
water resources, or in general the water balance, can be signifi-
cantly altered with any changes in temperature.
Warming will increase the frequency and intensity of tropical
storms in the Indian Ocean and consequently, that coastal areas
may be subject to flooding due to rising sea levels (Nicholls et al.,
2007; Rahmstorf, 2010). Most studies over southern Africa project
a temperature increase of around 3 °C. For example, Mujere and
Mazvimavi (2012) projected a 3 °C maximum temperature in-
crease for Mazoe catchment in Zimbabwe; Beck and Bernauer
(2011), a 2.9 °C maximum increase for the Zambezi Basin; Graham
et al. (2011) a3°C maximum temperature increase for Thukela
Catchment, South Africa; Hewitson and Tadross (2011) a3°C
maximum temperature increase for South Africa, Swaziland and
Lesotho. Other scholars projected temperature changes of between
2 and 5 °C for different areas within southern Africa including Losjö
et al. (2007); Schulze (2005a);Tadross et al. (2005), Matondo et al.
(2004), Arnell et al. (2003), Hudson and Jones (2002) and New
(2002). All projections show a temperature increase for southern
Africa. However, different regions are characterised by different
ranges of temperature increases, with the wet tropical areas near
the equator (parts of Zambia and DRC) having a lower temperature
changes as compared to the dry regions of Botswana, Namibia and
parts of Zimbabwe and South Africa. Projections have shown that,
the arid and semi-arid areas are likely to get drier due to climate
change than more humid areas in countries such as Tanzania or
Zambia (IPCC, 2008). However, the different scholars used different
global climate models in their projections. More so, others relied
on use of a single GCM (e.g. Mujere and Mazvimavi, 2012). Addi-
tionally, only a few studies used RCM (e.g. Engelbrecht, 2005;
Schulze et al., 2005b; Tadross et al., 2005) despite these having a
better spatial resolution for better temperature projections.
Most studies concluded that, based on future climate modelling
results, southern Africa’s climate will become hotter and drier. This
warming will be greatest over the interior and semi-arid margins
of southern Africa, the Sahel and central Africa. Projections show
that temperature changes will not be uniform over the region:
the central, southern land mass extending over Botswana, parts
of north-western South Africa, Namibia and Zimbabwe are likely
to experience the greatest warming of 0.2–0.5 °C per decade
(Christensen et al., 2007).
3.2. Rainfall
Rainfall trends have been extensively studied in assessing im-
pacts of climate change on water resources. Most scholars concur
that, even without climate change, rainfall exhibits extreme vari-
ability in time and space over southern Africa. While there is
S. Kusangaya et al. / Physics and Chemistry of the Earth 67–69 (2014) 47–54 49
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uncertainty on the magnitude of climate change impacts on rain-
fall in southern Africa (Christensen et al., 2007), the IPCC
(2007a,b) suggest that climate change will decrease rainfall. Many
models project that by 2050 the interior of southern Africa will
experience decreased rainfall during the growing season due to
reductions in soil moisture and runoff. Additionally, many climate
change models, predict a 5–15% decrease of growing season rain-
fall in southern Africa (IPCC, 2001). Hulme (1992) predicted a 5–
10% reduction in rainfall and Mazvimavi (2011) projected a 3–
23% decrease in rainfall under climate change in southern Africa.
Several scholars share the same view (e.g. Hulme et al., 2001; Ar-
nell et al., 2003) and have predicted that the region will be charac-
terised by below-normal rainfalls and frequent droughts in future.
Although most studies (e.g. Kenabatho et al., 2012; Mhlanga et al.,
2012; Zhu and Ringler, 2010; Andersson et al., 2009; Engelbrecht
et al., 2008; Christensen et al., 2007; Tadross et al., 2005; Matondo
et al., 2004; Arnell et al., 2003; Hudson and Jones, 2002) indicate
future reduction in rainfall of up to 50%, projected future changes
in mean seasonal rainfall in southern Africa are less well defined
(Manase, 2010; Schulze et al., 2012).
Scientific evidence points to an increased inter-annual variabil-
ity, with extremely wet periods and more intense droughts in dif-
ferent countries in future. Besides volumes, rainfall patterns are
also expected to change in intensity and frequency, resulting in
more extreme events and longer periods between rainfalls
(Christensen et al., 2007). At the same time, the demand for water
in the region is increasing rapidly due to population growth and
economic development (AWDR, 2006). Still, in the region, most
livelihoods are dependent rain-fed agriculture, that which will be
affected by reduction in rainfall under climate change (Thornton
et al., 2009, 2010).
Although most rainfall projections based on global circulation
models show reduced rainfall for much of southern Africa (see
for example Arnell, 2003, 2004; Nicholson, 2001; Mazvimavi,
1998; Hudson and Jones, 2002; Matondo et al., 2004; Graham
et al., 2011; Zhu and Ringler, 2010), to date there has not been con-
sensus on the magnitude of potential rainfall reductions due to (1)
use of different climate models, (2) variations in climate change
model outputs, (3) different responses to climate change due to
differences in catchment physiographic characteristics, among
other factors (Leavesley, 1994; Xu, 1999; Schulze, et al., 2010).
Some models, on the other hand, show that other areas will expe-
rience increased rainfall amounts. For example, Schulze et al.
(2010) and Tadross et al. (2011) reported that the north eastern
regions of South Africa will actually experience increased rainfall
under different climate change scenarios.
4. Hydrological responses to climate change
Changes in climate, with resultant increasing temperatures and
changing rainfall patterns may alter hydrological responses
(Kundzewicz et al., 2007). Most assessments of climate change
impacts have been primarily undertaken at macro and regional
scales, masking the complex hydrological interactions at the local,
catchment scale (Schulze, 2000a). As a result reported streamflow
responses to climate change are varied, both spatially and
temporally.
Although most studies have been confined to modelling hydro-
logical responses to climate only, Warburton et al. (2010) showed
that land use and land cover play a significant role in controlling
hydrological responses. Additionally, streamflow is influenced not
only by climate, but by numerous other human activities such as
catchment land use changes, inter-basin water transfers, water
abstractions, return flows or reservoir construction (Warburton
and Schulze, 2005). These may conceal, obliterate, or reverse cli-
mate change induced trends. Ultimately, streamflow is the integra-
tion of several aspects of climate over both time and space, hence
trends in one driver may be offset by opposite trends in other
hydrological drivers such as catchment soils, geology or land use
(Warburton et al., 2010; Arnell et al., 2003; Schulze et al., 2011).
Despite the above challenges, the hydrological responses to cli-
mate change in the southern Africa have been investigated using
mostly rainfall–runoff hydrological models. According to Schulze
(2005b) rainfall runoff models are invaluable tools in simulating
information for use in making decisions for water resources plan-
ning and management including evaluating impacts of climate
change on water resources. The following section reviews some
of the studies on hydrological responses to climate change under-
taken in southern Africa.
4.1. Streamflow projections under climate change
Several runoff projections under climate change have been pro-
vided by different scholars for southern Africa. River runoff and
water availability are projected to decrease by 10–30% in the dry
tropics (IPCC, 2007a,b). Arnell (1999) predicted a reduction in run-
off of 26–40% in the Zambezi river system, as a result of reduced
rainfall and increased evaporation. Evaporative increases of 40%,
for example, could result in reduced outflows from reservoirs.
Additionally, the projected increased frequency of droughts will
most likely increase the frequency of low storage episodes (see
e.g. Desanker and Magadza, 2001), which will inevitably affect
for example, future hydro power generation from such dams as
the Kariba and Cabora Bassa (Yamba et al., 2011). Cambula
(1999) (cited in Desanker and Magadza (2001)) in their work on
the Zambezi basin in Mozambique, for example, showed a decrease
in surface and subsurface runoff of about 40% or more under cli-
mate change. Yamba et al. (2011) further showed that under cli-
mate change, the hydroelectric power generation potential for
the Zambezi Basin will be gradually reduced for existing and pro-
posed hydroelectric power schemes owing to increased frequency
of droughts (reducing run-off and hence reservoir storage
capacity).
The general conclusion from most studies is that streamflow is
projected to decrease by 2050. For example, Matondo (2012) pro-
jected that for Swaziland streamflow will decrease by up to 40%;
Beck and Bernauer (2011) projected a decrease of up to 20% for
the Zambezi catchment; Andersson et al. (2010) (and Losjö et al.,
2007), up to 75% decrease for the Pungwe catchment; Zhu and
Ringler (2010), up to 35% decrease for the Limpopo catchment;
Graham et al. (2011), up to 18% decrease for Thukela catchment,
South Africa; Andersson et al. (2006), up to 20% decrease for the
Okavango in Botswana; Arnell (1999), up to 45% decrease for the
Zambezi, Limpopo, Ruvhuma and Orange catchments; Mazvimavi
(1998), up to 50% decrease for the Gwayi, Odzi and Sebakwe catch-
ments in Zimbabwe. However, some catchments were projected to
experience increases in streamflow like parts of the Thukela catch-
ment in South Africa (Graham et al., 2011; Andersson et al., 2009)
of between 16% and 38%. Also some catchments in Swaziland were
projected to have increased streamflow of between 5% and 34% as
modelled by Matondo (2012), Mhlanga et al. (2012) and Matondo
et al. (2004).
From the above studies, there is still no consensus on the mag-
nitude of decrease or increase of streamflow, although most stud-
ies conclude that streamflow will decrease. To reduce such
uncertainty, more information can be derived from the use of
downscaled GCMs and subsequently, distributed hydrological
models especially on modelling streamflow changes under climate
change. Additionally, use of an assemblage of climate models is
likely to improve projected streamflow changes for southern
Africa.
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5. Discussion: Challenges in modelling climate change impacts
on water resources
Many challenges encountered in climate change modelling are
detailed in the literature. The following sections describe some of
the possible challenges in modelling the impacts of climate change
on water resources in southern Africa.
5.1. Use of emission scenarios in climate change modelling
Tadross et al. (2011) pointed out that although global circula-
tion models can reliably and skilfully project changes in tempera-
ture, these models are often less-skilled in translating that
information into changes in rainfall (and other parameters) at
the local scale. Rainfall is, however, the main driver for hydrologi-
cal modelling (Hughes, 2004; Schulze, 1995; Jewitt and Schulze,
1999). This implies that hydrological models used for climate
change impacts analysis also inherit the uncertainties from climate
models. Other sources of uncertainty in climate change modelling
include: choice of climate models, quality of historical data,
methods of downscaling and boundary uncertainty (Hewitson
and Tadross, 2011). Considering all the other possible sources of
uncertainty, the output from climate models will therefore suffer
from compounded uncertainty. For southern Africa, while it has
always been recognised that uncertainty exists it has not been
properly quantified, nor consistently included as part of the risk
in decision making in water resources management.
5.2. Skills limitations
Mazvimavi (2011) also pointed out that southern Africa lacks
skills, for developing and implementing effective responses to cli-
mate change, and for timely dissemination of relevant information
to land and water users. Mouton et al. (2010) reported that scien-
tific research is mainly confined to South Africa in southern Africa,
with limited research and publication elsewhere.
5.3. Climate modelling and downscaling constraints
Global climate model projections are considered as the most ad-
vanced tools for projecting future climate change scenarios and
have been extensively used in the study of climate change; how-
ever, they operate on a coarse spatial resolution. In response to
this, downscaling methods have improved substantially, with re-
gional downscaling having been undertaken for southern Africa.
According to Hulme et al. (2001) and Nikulin et al. (2012)
downscaling of GCM outputs to finer spatial and temporal scales
has, however, received relatively little attention in Africa, despite
the widespread use of downscaled outputs in other parts of the
world. The Coordinated Regional Downscaling Experiment (COR-
DEX) program, established by the World Climate Research Program
(WCRP) was a direct response to the need of downscaled products
in climate modelling (Jones et al., 2011). CORDEX-Africa is aimed at
developing a coordinated framework for generating improved re-
gional climate change projections, as well as to meet the growing
demand for high-resolution downscaled projections to inform cli-
mate change impact and adaptation studies (Jones et al., 2011;
Nikulin et al., 2012). Thus downscaling for southern Africa
facilitates analysis of climate change at the scale at which water re-
sources are managed since Regional Climate Models have achieved
spatial resolution of 10–50 km
2
(Tadross et al., 2011; Nikulin et al.,
2012).
Although, the use of downscaled RCM reduces the spatial scale,
Wilby et al. (2009) cautioned that different circulation schemes
and downscaling methodologies yield noticeably different regional
climate change scenarios, even when common sets of RCM outputs
are used. For example Nikulin et al. (2012) noted that projections
in precipitation have larger uncertainties compared to the temper-
ature ones particularly for annual and diurnal cycles of precipita-
tion. Consequently, impacts of climate change on water
resources, particularly hydrological responses under such uncer-
tainty are still to be evaluated for southern Africa.
5.4. Rainfall runoff modelling and climate change
Most of the basins in the southern Africa are classified as poorly
gauged due to the rather low and unevenly distributed hydro-
meteorological stations (Nikulin et al., 2012; Mazvimavi, 2003;
Saunyama, 2008). Within this data scarce region, water resources
planning and management decisions are frequently based on sim-
ulated information using hydrological models. The most widely
used hydrological models are the (a) Pitman model, which is a con-
ceptual, semi-distributed monthly time-step model (Hughes,
2004; Hughes et al., 2006), developed by Pitman in 1973, and (b)
The ACRU model, developed by Schulze (and Smithers) (Schulze,
2005b; Smithers and Schulze, 1995) which is a physical conceptual
model capable of daily time step modelling.
Rainfall–runoff hydrological models have been used widely for
estimating available water resources or assessing impacts of devel-
opment needs or climate change. Still, as mentioned earlier, both
hydrological models and regional climate models are simplified
representations of reality which are frequently based on inade-
quate input data and uncertainties in parameter values and poor
mathematical representation of processes. This makes both climate
and hydrological models subject to predictive uncertainty. Renard
et al. (2010) summarises the main sources of predictive uncer-
tainty as: (a) data (e.g. spatial representation and measurements
of input and output time-series), (b) model (e.g. process descrip-
tions and mathematical implementation), and (c) the modelling
approach (e.g. the method chosen for parameter estimation). An
important science question that now arises is how predictive
uncertainty can be acknowledged, quantified and ultimately re-
duced for climate change modelling as well as for hydrological
modelling? Evaluation of uncertainty is necessitated by the need
to give an accurate and/or optimum basis for decision making
regarding future hydrological responses under climate change. To
date compounded uncertainty from use of downscaled climate
data and of hydrological models in climate change impact analysis
has not been evaluated for southern Africa, despite the clear need
to ascertain, acknowledge and quantify such uncertainty.
6. Conclusion
The potential wide ranging impacts of climate change on water
resources (availability, accessibility and demand) as reviewed
above make a compelling case for the need to strengthen inte-
grated water resources management institutions in respective
southern Africa countries since decisions for water resources plan-
ning and management (including aspects of climate change im-
pacts) are made within such structures. At catchment level it is
then possible to make maximum use of current and future ad-
vances in the fields of geographical information systems, remote
sensing, information management, and computer science in evalu-
ating climate change impacts on water resources.
Incorporation of climate change information should be done
even at regional level through such structures as the SADC protocol
on shared water courses, as the region has 12 shared river basins
(namely: Zambezi, Limpopo, Orange, Pungwe, Inkomati, Okavango,
Ruvuma, Buzi, Kunene, Save and Usutu basins). Given such link-
ages, the projected reduction in the stream flow for the Zambezi
S. Kusangaya et al. / Physics and Chemistry of the Earth 67–69 (2014) 47–54 51
Author's personal copy
basin, for example, will inevitably affect all the eight SADC riparian
states (home to over 40 million people) in terms of water availabil-
ity (e.g. for irrigation or hydroelectric power generation), wetlands,
agriculture (Thornton et al., 2009), and tourism (Beck and
Bernauer, 2011). It thus become imperative to enable collaborative
regional training and research that critically evaluates the poten-
tial impacts of climate change on water resources in different
southern Africa hydro-climatic regions so as to inform policy and
improve adaptation measures.
Whilst most of the studies reviewed above looked at the poten-
tial impacts of climate change on water resources, it is argued here
that the focus of the studies were mostly sub-regional and country
level, and relying mostly on use and interpretation of GCM projec-
tions and only until recently, few studies used downscaled RCMs.
As such this makes for a compelling case for catchment level stud-
ies in southern Africa since water resources management decisions
are undertaken at catchment level. Such research should therefore
focus on the following: (a) improving use of downscaled climate
change information for input into hydrological modelling, (b) refin-
ing use of earth observation and in situ data to increase under-
standing and improve prediction of climate change, (c) improving
the utility of available model outputs by acknowledging and quan-
tifying compounded predictive uncertainty.
Addressing the above research issues will ultimately help ad-
dress problem areas related to a number of climate and hydrolog-
ical modelling issues discussed above, including parameter
estimation, temporal and spatial scale of application, validation,
climate-scenario generation, data, and modelling tools. Solutions
to these problems would significantly improve the capability of
models to assess the effects of climate change on water resources
in southern Africa; hence water resources evaluation and manage-
ment under a changing climate.
Acknowledgements
We would like to thank the Applied Centre for Climate and
Earth Systems Science (ACCESS) for supporting this research work
by providing funds for undertaking the PhD research under the
theme ‘‘Climate Change Impacts and Adaptation’’. We would fur-
ther like to thank the anonymous reviewers and editor for com-
ments and suggestions on the manuscript.
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