VULNERABILTY ASSESSMENT OF THE SURFACE WATER RESOURCES IN
SWAZILAND DUE TO THE IMPACT OF CLIMATE CHANGE AND
VARIABILITY
Jonathan I. Matondo1 and Saico S. Singwane1
Abstract
It has been established that climate change in the next 100 years will be due to
anthropogenic greenhouse gas emissions. The major effect of the increase of greenhouse
gas emissions in the atmosphere is global warming and thus changes in temperature,
precipitation and the environment (IPCC, [1]). A calibrated WatBal model was used in
assessing the vulnerability of the surface water resources in Swaziland due to climate
change. Two scenarios (dry and wet year) were considered given climate change. The
WatBal model was used to simulate future stream flows at each of the selected key
gauging stations in each catchment (Usuthu, Komati and Mbuluzi) using inputs
(precipitation and potential evapotranspiration) from representative GCMs results for
Swaziland given climate change. The water stress index for each of the sub-catchments
was computed and used in assessing the vulnerability of the water resources in the
country given climate change for the dry and wet year scenario. Simulation results show
that the Komati at GS30 and the Usuthu at GS7 will face a severe water stress (196.6%
and 728.9%, respectively), while the Mbuluzi at GS 32, the Usuthu at GS 16 and GS 19
will face a high water stress (60.9%, 72.8% and 42.2% respectively) given climate
change and dry year scenario. However, the Usuthu at GS6 and GS9 will face a moderate
water stress (36.0% and 37.2% respectively) given climate change and dry year scenario.
The Komati at GS30 and the Usuthu at GS7 will continue to face a severe water stress
(86.5% and100.5%, respectively), while the Mbuluzi at GS32, the Usuthu at GS2 and
GS19 will face a low water stress (18.2%, 19.56% and 11.63% respectively) and the rest
of the sub-catchments (Mbuluzi at GS3, Usuthu at GS5, GS9, GS15 and GS6) will have
no water stress given climate change and wet year scenario. Therefore, infrastructure
development (groundwater, water storage and distribution facilities etc.) is a key
adaptation strategy to the expected impacts (floods and droughts) of climate change in the
country especially given a dry year scenario.
, Keywords: Vulnerability, Climate change, Water stress, Simulation, WatBal model
1 Introduction
Swaziland which lies between latitude 25o to 27.5o south and between Longitude 30o to
32.5o east enjoys a subtropical climate that is characterised by hot and wet summers and cold and
dry winters. Variations in climatic conditions occur within the six physiographic regions (Figure
1) giving rise to three clearly distinguishable climate types (i.e. Cwb, Cwa. and Bsh). Highveld
and Upper Middleveld are characterized by a Cwb climate. Cwb is a mild humid climate with a
dry winter and warm summer with the warmest month below 22ºC (Strahler and Strahler, [2]).
Lower Middleveld and Lubombo range have a Cwa climate whilst the Western and Eastern
Lowveld have a Bsh climate (Murdoch, [3]).
Cwa is a mild humid climate with a dry winter and a hot summer with warmest month
over 22ºC. Bsh is a semiarid climate which is dry-hot with a mean annual temperature over 18ºC
(Strahler and Strahler, 1992). Mean annual rainfall ranges from about 1500 millimeters in the
Highveld to just >500 millimeters in the Lowveld (Table 1). Highveld temperatures normally
exceed 33oC in mid-summer (Dec-Jan). The Lowveld, on the other hand experience a large
diurnal temperature range, with maximum temperatures reaching the upper thirties. Semi-arid
pockets are found in this region, which is also liable to desertification.
Table 1: Average annual rainfall and temperature in each physiographic region
Physiographic Region Annual Rainfall (mm) Annual Temperature (oC)
Highveld 1 500 – 900 17.6 – 16.3
Middleveld 810 – 580 20.5 – 19.3
Lowveld >500 22.4 - 21.3
Lubombo 710 19.2
,Figure 1: Physiographic regions of Swaziland
Source: National Meteorological Services [4]
The water sources in Swaziland are mainly surface waters (rivers, reservoirs), ground
water and atmospheric moisture. There are seven drainage basins in Swaziland and these are:
Lomati (1111 km2), Komati (7371 km2), Mbuluzi (3100 km2), Usutu (12903 km2), Ngwavuma
(1305 km2), Pongola (280 km2) and Lubombo (125 km2) (see Figure 2).
Anthropogenic greenhouse gas warming up has been considered to be the major potential
mechanism of climate change over the next few hundred years (IPCC, [1]). A number of gases
that occur naturally in the atmosphere in small quantities are known as “greenhouse gases”.
Water vapour (H2O), carbon dioxide (CO2), ozone (O3), methane (CH4), and nitrous oxide (N2O)
trap solar energy in much the same way as do the glass panels of a greenhouse or a closed
automobile. However, the earth’s atmosphere has been kept some 30 o Celsius hotter than it
would otherwise be, making it possible for humans and other living things to exist on earth
because of the natural greenhouse gases effect (IPCC, [1]). This is by the trapping of the
outgoing solar energy and thus making the earth 30oC warmer that it would otherwise be without
the natural greenhouse gases.
, Figure 2: Location of Swaziland’s main river basins and corresponding stream flow gauging
stations (Source: Ministry of Natural Resources and Energy, Department of Water Affairs [5]
Human activities, however, are now raising the concentrations of these gases in the
atmosphere and thus increasing their ability to trap energy. The global greenhouse gas emissions
due to anthropogenic activities have increased since pre-industrial times with an increase of
about 70% between 1970 and 2004 (IPCC, [6]). Human-made carbon dioxide which, is the most
important contributor to the enhanced greenhouse gases effect, comes mainly from the use of
SWAZILAND DUE TO THE IMPACT OF CLIMATE CHANGE AND
VARIABILITY
Jonathan I. Matondo1 and Saico S. Singwane1
Abstract
It has been established that climate change in the next 100 years will be due to
anthropogenic greenhouse gas emissions. The major effect of the increase of greenhouse
gas emissions in the atmosphere is global warming and thus changes in temperature,
precipitation and the environment (IPCC, [1]). A calibrated WatBal model was used in
assessing the vulnerability of the surface water resources in Swaziland due to climate
change. Two scenarios (dry and wet year) were considered given climate change. The
WatBal model was used to simulate future stream flows at each of the selected key
gauging stations in each catchment (Usuthu, Komati and Mbuluzi) using inputs
(precipitation and potential evapotranspiration) from representative GCMs results for
Swaziland given climate change. The water stress index for each of the sub-catchments
was computed and used in assessing the vulnerability of the water resources in the
country given climate change for the dry and wet year scenario. Simulation results show
that the Komati at GS30 and the Usuthu at GS7 will face a severe water stress (196.6%
and 728.9%, respectively), while the Mbuluzi at GS 32, the Usuthu at GS 16 and GS 19
will face a high water stress (60.9%, 72.8% and 42.2% respectively) given climate
change and dry year scenario. However, the Usuthu at GS6 and GS9 will face a moderate
water stress (36.0% and 37.2% respectively) given climate change and dry year scenario.
The Komati at GS30 and the Usuthu at GS7 will continue to face a severe water stress
(86.5% and100.5%, respectively), while the Mbuluzi at GS32, the Usuthu at GS2 and
GS19 will face a low water stress (18.2%, 19.56% and 11.63% respectively) and the rest
of the sub-catchments (Mbuluzi at GS3, Usuthu at GS5, GS9, GS15 and GS6) will have
no water stress given climate change and wet year scenario. Therefore, infrastructure
development (groundwater, water storage and distribution facilities etc.) is a key
adaptation strategy to the expected impacts (floods and droughts) of climate change in the
country especially given a dry year scenario.
, Keywords: Vulnerability, Climate change, Water stress, Simulation, WatBal model
1 Introduction
Swaziland which lies between latitude 25o to 27.5o south and between Longitude 30o to
32.5o east enjoys a subtropical climate that is characterised by hot and wet summers and cold and
dry winters. Variations in climatic conditions occur within the six physiographic regions (Figure
1) giving rise to three clearly distinguishable climate types (i.e. Cwb, Cwa. and Bsh). Highveld
and Upper Middleveld are characterized by a Cwb climate. Cwb is a mild humid climate with a
dry winter and warm summer with the warmest month below 22ºC (Strahler and Strahler, [2]).
Lower Middleveld and Lubombo range have a Cwa climate whilst the Western and Eastern
Lowveld have a Bsh climate (Murdoch, [3]).
Cwa is a mild humid climate with a dry winter and a hot summer with warmest month
over 22ºC. Bsh is a semiarid climate which is dry-hot with a mean annual temperature over 18ºC
(Strahler and Strahler, 1992). Mean annual rainfall ranges from about 1500 millimeters in the
Highveld to just >500 millimeters in the Lowveld (Table 1). Highveld temperatures normally
exceed 33oC in mid-summer (Dec-Jan). The Lowveld, on the other hand experience a large
diurnal temperature range, with maximum temperatures reaching the upper thirties. Semi-arid
pockets are found in this region, which is also liable to desertification.
Table 1: Average annual rainfall and temperature in each physiographic region
Physiographic Region Annual Rainfall (mm) Annual Temperature (oC)
Highveld 1 500 – 900 17.6 – 16.3
Middleveld 810 – 580 20.5 – 19.3
Lowveld >500 22.4 - 21.3
Lubombo 710 19.2
,Figure 1: Physiographic regions of Swaziland
Source: National Meteorological Services [4]
The water sources in Swaziland are mainly surface waters (rivers, reservoirs), ground
water and atmospheric moisture. There are seven drainage basins in Swaziland and these are:
Lomati (1111 km2), Komati (7371 km2), Mbuluzi (3100 km2), Usutu (12903 km2), Ngwavuma
(1305 km2), Pongola (280 km2) and Lubombo (125 km2) (see Figure 2).
Anthropogenic greenhouse gas warming up has been considered to be the major potential
mechanism of climate change over the next few hundred years (IPCC, [1]). A number of gases
that occur naturally in the atmosphere in small quantities are known as “greenhouse gases”.
Water vapour (H2O), carbon dioxide (CO2), ozone (O3), methane (CH4), and nitrous oxide (N2O)
trap solar energy in much the same way as do the glass panels of a greenhouse or a closed
automobile. However, the earth’s atmosphere has been kept some 30 o Celsius hotter than it
would otherwise be, making it possible for humans and other living things to exist on earth
because of the natural greenhouse gases effect (IPCC, [1]). This is by the trapping of the
outgoing solar energy and thus making the earth 30oC warmer that it would otherwise be without
the natural greenhouse gases.
, Figure 2: Location of Swaziland’s main river basins and corresponding stream flow gauging
stations (Source: Ministry of Natural Resources and Energy, Department of Water Affairs [5]
Human activities, however, are now raising the concentrations of these gases in the
atmosphere and thus increasing their ability to trap energy. The global greenhouse gas emissions
due to anthropogenic activities have increased since pre-industrial times with an increase of
about 70% between 1970 and 2004 (IPCC, [6]). Human-made carbon dioxide which, is the most
important contributor to the enhanced greenhouse gases effect, comes mainly from the use of
