ASSESSING RUNOFF CHANGES IN MAJOR CATCHMENTS IN ESWATINI DUE TO
CLIMATE CHANGE
Jonathan I. Matondo, University of Swaziland, Swaziland
Abstract:
It has been repor ted that 1 9 9 25 -0 0 6a
re the warm est year s in the
his t ory of i n s t r umen t a t i o n (s i n c e 1850a) n d the globa l
sur f a c e t em p e r a t u r e ri s e is at tr i b u t e d to the gre e n h o u s e
ga s e s eff e c t . The comb i n e d g l o b a l l a n d an d oc e a n su r f a c e
t em p e r a t u r e for Ju l y 2010
wa s t h e s e c o n d wa rme s t on rec o rd,
beh in d 1
998
, a n d t h e wa rm e s t a v e r a g e Ja n u a r y-Ju l y on re c o rd.
The eff e c t s o f g l o b a l wa rmi n g w i l l b r i n g ch a n g e s i n annu a l av e r a g
values in the order of ±20%.
The south e r n African r egion has bee n p r oject e d to receive less p r ecipitation an d
Swaziland is no exception. The average results (precipitation, potential evapotranspiration) of 12
gen e r al cir culation mo d els ( GCMs) in the futu r e ( 2 0 2 1 to 2 0 6 0 ) an d
the obs e r ve d st r ea m flows (1961- 2000) we r e input to a calib r at e d rainfall runo ff
model (WatBal model) in order to determine the water resources in four catchments in Swaziland
un d e r exp ec t e d climat e chan g e . Simulation results show that, the p res e n t
st r ea m flow lie within the 9 5 % con fi d enc e inte r val of the p roject e d flows in all
the catch m e n t s . This implies that the r e is no signi ficanc e diffe renc e betw e e n
the obs e r ve d an d p r oject e d st r ea m flow at 5% con fi d enc e level. Howeve r , the
r uno f f ch a n g e be t w e e n th e 2
.5
% an d 9
7.5
% qu a n t i l e r ang e s f r om -1
7.4
to 2 6 6. -3
; 1 2. to 1 8 1. -4
; 0 3. to 2 7 7. ;an
d -4 0 8. to 3 4 9. %
in the Kom ati, Mbuluzi,
,Us u t u a n d Ngw a v u m a c a t c h m e n t s re s p e c t i v e l y a n d the me d ian of the
r uno ff chan g e is neg a tiv e fo r most of the mont h s in th r ee catch m e n t s (Usutu,
M buluzi an d Ngwavu m a ) exce p t fo r the Komati catch m e n t . Thus, the r e will be
less r uno ff in the th r ee catch m e n t s un d e r exp ec t e d climat e chan g e . The r efo r e,
p r opos e d a d apt a tio n options to climat e chan g e fo r Swazilan d a r e: e fficient
wate r use (at domes tic an d fa r m level), wast e w a t e r recycling, rainwat e r
ha r ves tin g, g r oun d wate r utilization, imple m e n t a tio n of integ r at e d wate r
resources management (IWRM), water resources development and inter-basin transfers.
Keywords: Climate change, streamflow simulation, runoff change, statistical significance,
ad aptation options
INTRODUCTION
Swaziland is bounded by the Republic of South Africa in the north, west and south and by
Mozam biq u e on the E ast. The r efo r e, Swazilan d is a lan dlocke d count r y with a
size of 1 7 4 0 0 km 2. The count r y is divid e d into fou r physiologic regions
na m ely; Highvel d , Middlevel d , Lowvel d an d Lubom b o. The Highvel d an d uppe r
Middlevel d a r e cha r act e r ize d by a Cwb climat e . The lowe r Middlevel d an d
Lubombo range have a Cwa climate whilst the western and eastern Lowveld have a Bsh climate
(M u rd och, 1970). The Highvel d r egion r eceive s the highe s t rainfall which rang e s
from 1 2 0 0 to 1 5 0 0 m m pe r yea r followe d by the Middlevel d with
annu al r ainfall r anging from 7 0 0 to 1 2 0 0 m m . The Lowvel d region
,r eceive s the lowest rainfall which rang e s f rom 500 to 700 m m pe r yea r while the
Lubombo plateau has similar climatic conditions to the Middleveld region.
The water sources in Swaziland are mainly surface waters (rivers, reservoirs),
g r oun d wa t e r an d a tmo s p h e r i c mo i s t u r e. The r e a r e s e v e n dra i n a g e ba s i n
Swazilan d an d these a r e: Lomati, Komati, Mbuluzi, Usutu, Ngwavuma, Pongola an d
Lu b om b o (se e F i g u r e 1).
Climate will always change due to the natu r al fo rcings of eccent ricity. Climate
c h a n g e s oc c u rr i n g ov e r t i m e s c a l e s s h o r t e r t h a n t h o s e a s s o c i a t e d w
forcing frequencies are defined as short- term. Climate fluctuations on time scales
of les s than 100
ye a r s a r e u s u a l l y con s i d e red as c l i m a t i c
var i a b i l i t y .
It has been considered that the major potential mechanism of climate change over the next few
hundred years will be anthropogenic green house gas warming
u p. A numb e r of ga s e s tha t occ ur na t u r a l l y in the
a tmo s p h e r e i n sma l l qua n t i t i e s a r e kn own a s “g reenh o u s e
g a s e s ” . Wa t e r v a p o u r (H 2 O), ca r bon dioxi d e (CO 2), ozone (O 3 ), methane
(CH 4), and nitrous oxide (N O) t r a p s o l a r e n e r g y i n mu c h t h e s a m e w a y a
2
do the glass panels of a greenhouse or a closed automobile. However, the earth’s
a tm o s p h e r e ha s be e n kep t s om e 30
o
Celsius hotte r than it woul d
o t h e rw i s e be, mak i n g it po s s i b l e for hum a n s and o t h e r
living th i n g s to ex i s t on e a r t h be c a u s e of the na t u r a l
gr e e n h o u s e g a s e s e f f e c t .
, Huma n a c t i v i t i e s , howe v e r , a r e now r a i s i n g t h e c o n c e n t r a t i o n s of th
atmosphe r e an d thus inc r easing thei r ability to t rap ene r gy. Ca rbon dioxi de levels
have risen from 280 ppm by volume since before the Industrial Revolution to
about 3 6 0 ppm by 1 9 9 0 (IPCC, 2 0 0 1 ) . Man- ma d e ca rbon dioxi de
which, is the most important contributor to the enhanced
gr e e n h o u s e ga s e s ef f e c t, c ome s ma i n l y f r om t h e use of
coal, oil, and natural gas. It is also released by the
d es t r u c t i o n of fore s t s and other na t u r a l sinks and
r es e r v o i r s t h a t a b s o r b c a r b o n d i o x i d e f r om t h e a i r .
The g l o b a l g r ee n hou s e ga s em i s s i o n s due t o an t h r o p o g e n i c ac t i v i t
increased since pre-industrial times with and increase of about 70% between
1970 an d 2004 (IPCC, 2007). T he IPCC ( 2007) als o re po rts
that the atmosphe r ic concent r ations of CO 2 (397ppm) and CH4 (1774ppb)
i n ye a r 200
ex
5 c e e d by f a r t h e n a t u r a l r an g e ov e r t h e l a s t 6500
,0
ye
0a r s. F
major contributor of global CO2, f o l l o w e d w i t h l a n d-u s e c h a n g e . It has
been established that the climate change in the next 100 years wil
anth r opogenic activities (IPCC, 2001). It has also been repo rte d that
1992
5-
00a6
r e t h e wa rme s t ye a r s i n t h e h i s t o r y o f i n s t r u m e n t a t i o n
(s i n c e 1850
a )n d t h e g l o b a l s u r f a c e t em p e r a t u r e r i s e i s due t o t h e g r e e
gases effect (IPCC, 2007). The major effect of theincreaseof anthropogenicgreen
house gas emissions in the atmosphere is global warming
a n d t h u s c h a n g e s i n pr e c i p i t a t i o n a n d t h e e n v i r o n m e n t . The
areas that are now dry-humid, semiarid and arid will become semiarid, arid and desert respectively.
CLIMATE CHANGE
Jonathan I. Matondo, University of Swaziland, Swaziland
Abstract:
It has been repor ted that 1 9 9 25 -0 0 6a
re the warm est year s in the
his t ory of i n s t r umen t a t i o n (s i n c e 1850a) n d the globa l
sur f a c e t em p e r a t u r e ri s e is at tr i b u t e d to the gre e n h o u s e
ga s e s eff e c t . The comb i n e d g l o b a l l a n d an d oc e a n su r f a c e
t em p e r a t u r e for Ju l y 2010
wa s t h e s e c o n d wa rme s t on rec o rd,
beh in d 1
998
, a n d t h e wa rm e s t a v e r a g e Ja n u a r y-Ju l y on re c o rd.
The eff e c t s o f g l o b a l wa rmi n g w i l l b r i n g ch a n g e s i n annu a l av e r a g
values in the order of ±20%.
The south e r n African r egion has bee n p r oject e d to receive less p r ecipitation an d
Swaziland is no exception. The average results (precipitation, potential evapotranspiration) of 12
gen e r al cir culation mo d els ( GCMs) in the futu r e ( 2 0 2 1 to 2 0 6 0 ) an d
the obs e r ve d st r ea m flows (1961- 2000) we r e input to a calib r at e d rainfall runo ff
model (WatBal model) in order to determine the water resources in four catchments in Swaziland
un d e r exp ec t e d climat e chan g e . Simulation results show that, the p res e n t
st r ea m flow lie within the 9 5 % con fi d enc e inte r val of the p roject e d flows in all
the catch m e n t s . This implies that the r e is no signi ficanc e diffe renc e betw e e n
the obs e r ve d an d p r oject e d st r ea m flow at 5% con fi d enc e level. Howeve r , the
r uno f f ch a n g e be t w e e n th e 2
.5
% an d 9
7.5
% qu a n t i l e r ang e s f r om -1
7.4
to 2 6 6. -3
; 1 2. to 1 8 1. -4
; 0 3. to 2 7 7. ;an
d -4 0 8. to 3 4 9. %
in the Kom ati, Mbuluzi,
,Us u t u a n d Ngw a v u m a c a t c h m e n t s re s p e c t i v e l y a n d the me d ian of the
r uno ff chan g e is neg a tiv e fo r most of the mont h s in th r ee catch m e n t s (Usutu,
M buluzi an d Ngwavu m a ) exce p t fo r the Komati catch m e n t . Thus, the r e will be
less r uno ff in the th r ee catch m e n t s un d e r exp ec t e d climat e chan g e . The r efo r e,
p r opos e d a d apt a tio n options to climat e chan g e fo r Swazilan d a r e: e fficient
wate r use (at domes tic an d fa r m level), wast e w a t e r recycling, rainwat e r
ha r ves tin g, g r oun d wate r utilization, imple m e n t a tio n of integ r at e d wate r
resources management (IWRM), water resources development and inter-basin transfers.
Keywords: Climate change, streamflow simulation, runoff change, statistical significance,
ad aptation options
INTRODUCTION
Swaziland is bounded by the Republic of South Africa in the north, west and south and by
Mozam biq u e on the E ast. The r efo r e, Swazilan d is a lan dlocke d count r y with a
size of 1 7 4 0 0 km 2. The count r y is divid e d into fou r physiologic regions
na m ely; Highvel d , Middlevel d , Lowvel d an d Lubom b o. The Highvel d an d uppe r
Middlevel d a r e cha r act e r ize d by a Cwb climat e . The lowe r Middlevel d an d
Lubombo range have a Cwa climate whilst the western and eastern Lowveld have a Bsh climate
(M u rd och, 1970). The Highvel d r egion r eceive s the highe s t rainfall which rang e s
from 1 2 0 0 to 1 5 0 0 m m pe r yea r followe d by the Middlevel d with
annu al r ainfall r anging from 7 0 0 to 1 2 0 0 m m . The Lowvel d region
,r eceive s the lowest rainfall which rang e s f rom 500 to 700 m m pe r yea r while the
Lubombo plateau has similar climatic conditions to the Middleveld region.
The water sources in Swaziland are mainly surface waters (rivers, reservoirs),
g r oun d wa t e r an d a tmo s p h e r i c mo i s t u r e. The r e a r e s e v e n dra i n a g e ba s i n
Swazilan d an d these a r e: Lomati, Komati, Mbuluzi, Usutu, Ngwavuma, Pongola an d
Lu b om b o (se e F i g u r e 1).
Climate will always change due to the natu r al fo rcings of eccent ricity. Climate
c h a n g e s oc c u rr i n g ov e r t i m e s c a l e s s h o r t e r t h a n t h o s e a s s o c i a t e d w
forcing frequencies are defined as short- term. Climate fluctuations on time scales
of les s than 100
ye a r s a r e u s u a l l y con s i d e red as c l i m a t i c
var i a b i l i t y .
It has been considered that the major potential mechanism of climate change over the next few
hundred years will be anthropogenic green house gas warming
u p. A numb e r of ga s e s tha t occ ur na t u r a l l y in the
a tmo s p h e r e i n sma l l qua n t i t i e s a r e kn own a s “g reenh o u s e
g a s e s ” . Wa t e r v a p o u r (H 2 O), ca r bon dioxi d e (CO 2), ozone (O 3 ), methane
(CH 4), and nitrous oxide (N O) t r a p s o l a r e n e r g y i n mu c h t h e s a m e w a y a
2
do the glass panels of a greenhouse or a closed automobile. However, the earth’s
a tm o s p h e r e ha s be e n kep t s om e 30
o
Celsius hotte r than it woul d
o t h e rw i s e be, mak i n g it po s s i b l e for hum a n s and o t h e r
living th i n g s to ex i s t on e a r t h be c a u s e of the na t u r a l
gr e e n h o u s e g a s e s e f f e c t .
, Huma n a c t i v i t i e s , howe v e r , a r e now r a i s i n g t h e c o n c e n t r a t i o n s of th
atmosphe r e an d thus inc r easing thei r ability to t rap ene r gy. Ca rbon dioxi de levels
have risen from 280 ppm by volume since before the Industrial Revolution to
about 3 6 0 ppm by 1 9 9 0 (IPCC, 2 0 0 1 ) . Man- ma d e ca rbon dioxi de
which, is the most important contributor to the enhanced
gr e e n h o u s e ga s e s ef f e c t, c ome s ma i n l y f r om t h e use of
coal, oil, and natural gas. It is also released by the
d es t r u c t i o n of fore s t s and other na t u r a l sinks and
r es e r v o i r s t h a t a b s o r b c a r b o n d i o x i d e f r om t h e a i r .
The g l o b a l g r ee n hou s e ga s em i s s i o n s due t o an t h r o p o g e n i c ac t i v i t
increased since pre-industrial times with and increase of about 70% between
1970 an d 2004 (IPCC, 2007). T he IPCC ( 2007) als o re po rts
that the atmosphe r ic concent r ations of CO 2 (397ppm) and CH4 (1774ppb)
i n ye a r 200
ex
5 c e e d by f a r t h e n a t u r a l r an g e ov e r t h e l a s t 6500
,0
ye
0a r s. F
major contributor of global CO2, f o l l o w e d w i t h l a n d-u s e c h a n g e . It has
been established that the climate change in the next 100 years wil
anth r opogenic activities (IPCC, 2001). It has also been repo rte d that
1992
5-
00a6
r e t h e wa rme s t ye a r s i n t h e h i s t o r y o f i n s t r u m e n t a t i o n
(s i n c e 1850
a )n d t h e g l o b a l s u r f a c e t em p e r a t u r e r i s e i s due t o t h e g r e e
gases effect (IPCC, 2007). The major effect of theincreaseof anthropogenicgreen
house gas emissions in the atmosphere is global warming
a n d t h u s c h a n g e s i n pr e c i p i t a t i o n a n d t h e e n v i r o n m e n t . The
areas that are now dry-humid, semiarid and arid will become semiarid, arid and desert respectively.
