The Vaal, Tugela, Mgeni and Orange River Catchments Receive Rainfall During Summer While the Breede River Catchment Receives Winter Rainfall

4 . 3 T r e n d s i n s e a s o n a l r a i n f a l l a n d r i v e r f l o w

The Vaal, Tugela, Mgeni and Orange River catchments receive rainfall during summer while the Breede River catchment receives winter rainfall. Southern African rainfall exhibits distinct seasonality within each year (Tyson, 1978), with the larger quantity of rainfall received between October and March (Mason, 1996), with the exception of the Western Cape. The December, January, February season is an important season because the atmospheric circulation over southern Africa is dominated by tropical circulation features (Landman et al. , 2008) e.g. tropical easterlies and easterly waves (Tyson, 1986). The following section investigates the seasonal rainfall trends in different regions across southern Africa and correlates these with seasonal river

flow.

4 . 3 . 1 V a a l R i v e r

The early (October and November), mid (December, January and February) and late (March and April) rainfall seasons at the three stations in the Vaal River catchment all indicate decreasing trends over the period 1909 to 2008 (Fig. 16 to Fig. 18), with only the early rainfall, mid rainfall and late rainfall seasons at the Villiers station displaying highly significant decreasing trends at the 95% significance level (Fig. 16). The early rainfall season displayed a 17% decline at both the Bloemhof and Klerksdorp stations and a 12% decline was observed at the Villiers station over the period 1940 to 2008. The mid season rainfall declined between 3 to 6% decline (Table 6) at all three stations over the period 1940 to 2008, but the percentage change in rainfall during the late season differed greatly between stations, indicating variability in late season rainfall. The late rainfall season at the Villiers station experienced the greatest decline in average rainfall

(37%), followed by a 25% decline at the Klerksdorp station over the period 1940 to 2008.

5 0

y = - 0 . 7 x + 2 0 2 . 2

= - 0 . 7

p = 1 . 0

y = - 0 . 5 8 x + 3 1 5 . 4 5

= - 0 . 5

p = 0 . 9 5

y = - 0 . 7 x + 1 3 6 . 4 1

= - 0 . 7

p = 0 . 9 9

Figure 16: Early, mid and late rainfall season trends for the Villiers rainfall station in the Vaal

River catchment.

5 1

y = - 0 . 1 3 x + 9 9 . 3 6

= - 0 . 1

p = 0 . 6 6

y = - 0 . 1 4 x + 2 3 4 . 3 4

= - 0 . 1

p = 0 . 6 1

y = - 0 . 0 9 x + 1 1 2 . 2 9

= - 0 . 0 9

p = 0 . 6 3

Figure 17: Early, mid and late rainfall season trends for the Bloemhof rainfall station in the Vaal River catchment.

5 2

y = - 0 . 0 0 5 x + 1 0 7

= - 0 . 0 0 5

p = 0 . 5 2

y = - 0 . 1 6 x + 2 8 9 . 4 3

= - 0 . 1 6

p = 0 . 6 7

y = - 0 . 4 x + 1 4 6 . 4 1

= - 0 . 4

p = 0 . 9 3

Figure 18: Early, mid and late rainfall season trends for the Klerksdorp rainfall station in the

Vaal River catchment.

5 3 Table 7: Percentage changes of rainfall and river flow (grey shade) observed over selected time

periods for the early, mid and late rainfall seasons at southern African stations.

P e r c e n t a g e c h a n g e f r o m t h e f i r s t h a l f t o t h e s e c o n d h a l f

S t a t i o n s P e r i o d

o f t h e r e c o r d i n g p e r i o d

M i d L a t e a r l y

V a a l R i v e r 1 9 4 0 - 1 9 7 4 , 1 9 7 5 - 2 0 0 8 6 9 5 1 1

B l o e m h o f 1 7 3 1 5

K l e r k s d o r p 1 7 5 2 5

V i l l i e r s 1 2 6 3 7

M g e n i R i v e r 1 9 5 1 - 1 9 8 0 , 1 9 8 1 - 2 0 0 8 4 4 3 2 5

M i s t l e y E s t a t e 0 . 3 4 7

N e w H a n o v e r 6 5 2

T u g e l a R i v e r 1 9 3 2 - 1 9 7 0 , 1 9 7 1 - 2 0 0 8 7 3 2 0 1 5

8 2 8 w a r t w a t e r

M o o r s i d e 7 6 1 4

T u g e l a F e r r y 1 4 8 6

B r e e d e R i v e r 1 9 4 4 - 1 9 7 6 , 1 9 7 7 - 2 0 0 8 3 5 2 2 2 7

M a l a b a r 3 8 2 4 8

T o u w s r i v i e r 7 2 1 6

r a n g e R i v e r 1 9 3 2 - 1 9 7 0 , 1 9 7 1 - 2 0 0 8 1 3 7 1 5

L i l l e 3 2 0 2

M i d d e l p l a a t s 0 . 6 8 9

Z a s t r o n 0 . 8 8 1 3

r a n g e R i v e r 1 9 6 7 - 1 9 8 7 , 1 9 8 8 - 2 0 0 6 1 0 2 1 2 3

L i l l e 5 1 7 1 0

M i d d e l p l a a t s 2 0 3 1 8

Z a s t r o n 6 1 2 3

T h a b a T s e k a 2 0 7 1 6

1 1 . 8 1 7 e m o n k o n g

The Vaal River flow experienced the greatest decline in flow (69%) during the early rainfall season over the period 1940 to 2008, which is possibly due to the large rainfall changes observed for the late rainfall season. The large rainfall changes during the late rainfall season will impact flow during the following early rainfall season. As previously discussed, the abstraction of water toward the latter period of record may be higher than the earlier period of record.

The average early season rainfall over the Vaal River catchment for the period 1905 to 1960 was

198.93mm, which decreased to 157.02mm for the period 1961 to 2006 at Villiers, indicating a

5 4 21% decline in rainfall. However, only a 9.5% decrease in average rainfall was observed during the mid rainfall season and a 33% decline in the late rainfall season. The Vaal River flow exhibits a highly significant decreasing trend for all three rainfall seasons (Fig. 19), which is consistent with the trend observed for the annual flow (section 4.2). The flow during the early rainfall season declined by 69% over the period 1940 to 2008, while the flow only declined by 5% and 11% during the mid and late rainfall seasons respectively. The 9.5% decrease in the average rainfall experienced during the mid rainfall season compares well with the 5% decrease in flow, since the smallest changes in flow and rainfall were experienced during the mid rainfall season. An examination of the Vaal River flow data for the months of the year (Appendix, Table 4) indicate a low flow period from May to October. The Vaal River exhibited particularly high flow during 1943, where even the months of traditional low flow, (May and July) displayed flow in the order of 300 to 400m 3/s, whilst the highest flow of the year recorded 796 m 3/s in November 1943 (Fig. 16). The correlation coefficients for the Vaal River flow with the rainfall at the three stations were weak for all seasons (Table 9). The correlation coefficient for the Vaal River flow and the Bloemhof station during the mid rainfall season was 0.3, which was the same correlation coefficient obtained for the annual relationship (section 4.1), indicating that the mid rainfall season is the main contributor to the annual correlation between rainfall at the Bloemhof station and the Vaal River flow.

4 . 3 . 2 O r a n g e R i v e r

The early rainfall season at the Lille station shows a 3% decreasing rainfall trend whilst the mid and late seasons indicate 17% and 10% increasing rainfall trends respectively over the period 1932 to 2008 (Fig. 20), suggesting that the mid and late rainfall seasons are the major contributors to the overall annual increasing trend observed for the annual rainfall at the Lille station (section 4.2). In contrast, the early and mid rainfall season at Middelplaats display a 0.6% and 8% respective increase in rainfall, whilst the late rainfall season experienced a 9%

decreasing trend over the period 1911 to 2008 (Fig.18). The early rainfall season at Zastron

5 5

y = - 0 . 3 x + 3 5 . 8

= - 0 . 3

p = 0 . 9 9

y = - 0 . 7 7 x + 8 3

= - 0 . 7

p = 0 . 9 9

y = - 0 . 6 3 x + 6 7

= - 0 . 6 3

p = 0 . 9 9

Figure 19: The Vaal River flow trends at the Vaal at Schoolplaats gauge during the early, mid and late rainfall seasons.

5 6 indicates a 0.8% increase in rainfall (Fig.19), whilst the mid and late season trends respectively show an 8% and 13% decline in rainfall over the period 1932 to 2008. There are large variations in the rainfall data between stations in the different rainfall seasons, as well as over different time periods, as reflected in Table 7. Comparing of the percentage change in seasonal rainfall (Table 6) at the South African rainfall stations with those for Lesotho is potentially problematic due to the considerable data gaps for the Lesotho stations. The early and mid rainfall seasons at the Semonkong station experienced 1% and 1.8% rainfall increases respectively, whilst the late rainfall season decreased by 17% over the period 1965 to 2006 (Fig. 25). The early, mid and late rainfall seasons at the Thaba Tseka station in Lesotho all show an increase in rainfall over the period 1965 to 2006 (Fig. 24). The early rainfall season at the Thaba Tseka station in Lesotho displays the steepest (Q=2) significant increasing rainfall trend in this study. Early summer rainfall is important in Lesotho, since crops are almost completely rain-fed (Hyde & Sekoli, 2000). To this end, the highly significant increase in rainfall during early rainfall season at the Thaba Tseka station (Fig. 24) is an important finding for long-term agricultural planning in Lesotho.

The Orange River flow data indicate increasing trends for all three rainfall seasons (Fig. 20) between 1914 and 2008. The Orange River is the only river in the study that did not exhibit a statistically significant trend in flow during the three rainfall seasons (Table 8). The correlation coefficients for the Orange River catchment were the greatest for the seasonal trends in this study, with Kendall tau values of 0.56 at the Lille, 0.55 at the Middelplaats and 0.6 at the Zastron stations during the mid rainfall season which were greater than the early and late rainfall seasons (Table 9). The correlation between the Orange River flow and rainfall was the best for the catchments studied. The correlation coefficients for the three stations during the three seasons

were in close range between 0.41 and 0.6 (Table 9).

5 7

y = - 0 . 2 2 x + 1 3 2 . 5

= - 0 . 2

p = 0 . 6 8

y = 0 . 4 7 x + 2 6 2 . 1

= 0 . 4 7

p = 0 . 7 7

y = 0 . 5 3 x + 1 3 8 . 5

= 0 . 1 5

p = 0 . 7 2

Figure 20: Rainfall trends for the early, mid and late rainfall seasons at Lille rainfall station in the

Orange River catchment.

5 8

y = 0 . 0 1 9 x + 1 0 7

= 0 . 1 9

p = 0 . 5 3

y = 0 . 1 4 x + 2 2 7 . 1

= 0 . 1 4

p = 0 . 6 2

y = 0 . 3 1 x + 1 4 5 . 4

= 0 . 3 1

p = 0 . 8 8

Figure 21: Rainfall trends for the early, mid and late rainfall seasons at Middelplaats rainfall

station in the Orange River catchment.

5 9

y = 0 . 0 9 7 x + 1 1 4 . 3

= 0 . 0 9 7

p = 0 . 6 8

y = - 0 . 2 5 x + 2 9 2 . 5

= - 0 . 2 5

p = 0 . 7 4

y = - 0 . 3 x + 1 5 3 . 2

= - 0 . 3

p = 0 . 8 5

Figure 22: Rainfall trends for the early, mid and late rainfall seasons at Zastron rainfall station in the Orange River.

6 0

y = 0 . 0 5 x + 1 0 4

= 0 . 0 5

p = 0 . 5 7

y = 0 . 4 3 x + 1 6 4

= 0 . 4 3

p = 0 . 8

y = 0 . 2 2 x + 1 5 4

= 0 . 2 2

p = 0 . 6 7

Figure 23: The Orange River flow trends during the early, mid and late rainfall seasons.

6 1

y = 2 . 0 x + 1 1 . 2 5

= 2

p = 0 . 9 9

y = 0 . 9 x + 2 4 6 . 4

= 0 . 9

p = 0 . 7 3

y = 0 . 9 3 x + 8 3

= 0 . 9

p = 0 . 8 8

Figure 24: Rainfall trends for the early, mid and late rainfall seasons at the Thaba Tseka rainfall station in Lesotho.

6 2

y = 0 . 7 9 x + 1 2 5 . 8 5

= 0 . 7 9

p = 0 . 8

y = 1 . 5 3 x + 2 2 4 . 6 5

= 1 . 5

p = 0 . 8 2

y = - 0 . 6 7 x + 1 3 3 . 7 9

= - 0 . 7

p = 0 . 7 8

Figure 25: Rainfall trends for the early, mid and late rainfall seasons at the Semonkong rainfall station in Lesotho.

6 3

4 . 3 . 3 T u g e l a R i v e r

The early rainfall season for the Moorside (Fig. 26) station indicates a 7% increase in rainfall, whilst the mid and late seasons exhibit a 6% and 14% decreasing trend respectively over the period 1914 to 2008. The Swartwater rainfall records display a 2% to 8% decreasing trend for all three seasons over the period 1932 to 2008. Rainfall during the early rainfall season at Tugela Ferry indicates a significant 14% increasing trend, whilst the mid and late rainfall seasons show a non-significant 8% and 6% increasing trend respectively (Fig. 28). Associated with the destructive heavy rainfall experienced over KwaZulu-Natal in September 1987 (Rautenbach, 1998), the Moorside (243.2mm), Swartwater (327mm) and Tugela Ferry (229mm) stations in the Tugela River catchment received the highest quantity of September rainfall during the period 1914 to 2008 (Appendix, Tables 15 to 17). According to Groisman et al. (2005), the summer (December, January and February) rainfall totals have not significantly changed over the period 1906 to 1997 for the eastern regions of southern Africa.

The Tugela River has experienced a 73%, 20% and 15% (Table 6) decline in flow during the early, mid and late rainfall seasons respectively, over the period 1927 to 2008 (Figure 29). The correlation coefficients Kendall tau (τ) ranged from 0.15 to 0.4, with the greatest correlation between the Moorside rainfall and the Tugela River flow for the mid (τ=0.41) and late (τ=0.35) rainfall seasons. The correlation coefficient was the greatest for the Swartwater early rainfall season (Table 9). The Tugela Ferry rainfall displayed the weakest correlation since the rainfall and river flow gauges are at the same location, thus confirming the greater control of upstream

catchment rainfall on river flow, as opposed to on-site rainfall.

4 . 3 . 4 M g e n i R i v e r

The early, mid and late rainfall seasons for the Mistley rainfall station became drier (Fig. 31) while the early, mid and late rainfall seasons for the New Hanover station became wetter (Fig.

30) over the period 1940 to 2008. Rainfall at the Mistley station during the late rainfall season

6 4

y = 0 . 0 2 4 x + 1 7 6 . 0 5

= 0 . 0 2

p = 0 . 5 4

y = - 0 . 4 2 x + 2 9 6 . 9

= - 0 . 4

p = 0 . 8 6

y = - 0 . 0 9 x + 1 4 0 . 5

= - 0 . 0 9

p = 0 . 6 2

Figure 26: Rainfall trends for the early, mid and late rainfall seasons at Moorside rainfall station

in the Tugela River catchment.

6 5

y = - 0 . 3 9 x + 1 9 5 . 2 1

= - 0 . 3 9

p = 0 . 7 8

y = - 0 . 3 6 x + 3 4 3 . 1

= - 0 . 3

p = 0 . 7 1

y = - 0 . 8 x + 1 2 0 . 5

= - 0 . 8

= 0 . 6 4 p Figure 27: Rainfall trends for the early, mid and late rainfall seasons at Swartwater rainfall

station in the Tugela River catchment.

6 6

y = 0 . 4 7 x + 1 5 3 . 2 7

= 0 . 4 7

p = 0 . 9 6

y = 0 . 5 8 x + 3 2 5 . 9

= 0 . 5 8

p = 0 . 9

y = 0 . 0 0 4 x + 1 4 0 . 7

= 0 . 0 0 4

p = 0 . 5 1

Figure 28: Rainfall trends for the early, mid and late rainfall seasons at Tugela Ferry rainfall

station in the Tugela River catchment.

6 7

y = - 0 . 6 2 x + 8 0

= - 0 . 6 2

p = 0 . 9 9

y = - 0 . 8 4 x + 1 9 2 . 9 7

= - 0 . 8

p = 0 . 9 8

y = - 0 . 8 4 x + 1 4 0

= - 0 . 8

p = 0 . 9 9 7

Figure 29: The Tugela River flow trends during the early, mid and late rainfall seasons.

6 8 exhibits a significant 7% decreasing trend (Table 7), whilst non significant 0.3% and 4% decreasing trends were observed during the early and mid rainfall seasons respectively over the period 1951 to 2008. The New Hanover rainfall station also displayed small percentage changes ranging between 2% and 6% for all the seasons over the period 1940 to 2008, however non significant increasing trends were observed. Potential reasons for the different trends were discussed in section 4.1.

The Mgeni River experienced a highly significant decreasing trend for the mid rainfall season while non significant decreasing trends were observed for the early and late rainfall seasons over the period 1951 to 2008 (Fig. 32). A 43% decline in flow was observed for the mid rainfall season while the flow during the late rainfall season declined by 25%, indicating a shift in seasonality. The flow in the late rainfall season did not decrease as much as that of the mid rainfall season possibly due to the low percentage declines of the rainfall during the mid rainfall season. The Kendall tau correlation coefficients between the Mgeni River flow and the rainfall at the Mistley and New Hanover stations were weak (Table 9). The strongest correlation coefficients of 0.3 and 0.29 were recorded between the flow and rainfall data at the New Hanover station during the mid and late rainfall seasons over the period 1951 to 2008.

4 . 2 . 5 B r e e d e R i v e r

The southwestern Cape Province receives winter rainfall mainly by means of cold fronts (Reason, 2002). The early (April to May), mid (June and July) and late (August and September) rainfall seasons for both the Touwsrivier (Fig. 34) and Malabar (Fig. 33) stations in the Breede River catchment display increasing trends over the period 1918 to 2008 and 1944 to 2008 respectively. A previous study also recorded significant precipitation increases during the wet season over the Western Cape Province (Kruger, 2006), however all the rainfall trends in the Breede River catchment in this study were insignificant, according to the Mann Kendall statistic at the 95% significance level. The Genesis GCM model projected an overall increase in winter

rainfall (Schulze & Perks, 2000).

6 9

y = 0 . 5 6 x + 1 6 7

= 0 . 5 6

p = 0 . 9

y = 0 . 4 5 x + 3 6 3 . 4

= 0 . 4 5

p = 0 . 7 5

y = 0 . 0 8 x + 1 5 3 . 7

= 0 . 0 8

p = 0 . 5 7

Figure 30: Rainfall trends for the early, mid and late rainfall seasons at New Hanover rainfall

station in the Mgeni River catchment.

7 0

y = - 0 . 4 x + 2 0 9 . 1

= - 0 . 4

p = 0 . 8 9

y = - 0 . 7 3 x + 3 7 9 . 4

= - 0 . 7

p = 0 . 8 5

y = - 0 . 7 8 x + 1 7 3 . 8

= - 0 . 7

p = 0 . 9 6

Figure 31: Rainfall trends for the early, mid and late rainfall seasons at Mistley rainfall station in

the Mgeni River catchment.

7 1

y = - 0 . 0 1 2 x + 7 . 1 9

= - 0 . 0 1 2

p = 0 . 7 6

y = - 0 . 2 5 x + 3 2

= - 0 . 2 5

p = 0 . 9 9

y = - 0 . 1 5 x + 2 1

= - 0 . 1 5

p = 0 . 9 2

Figure 32: The Mgeni River flow trends during the early, mid and late rainfall seasons.

7 2 The percentage changes for the Malabar and Touwsrivier rainfall stations increased by 24% and 21% during the mid rainfall season, while the rainfall increased by 8% and 6% at the Malabar and Touwsrivier stations during the late rainfall season respectively, over the period 1944 to 2008. However the rainfall at the Malabar station increased by 38% during the early rainfall season, whilst the rainfall only increased by 7% at the Touwsrivier station during the early rainfall season over the period 1944 to 2008. The river flow at Bree at Ceres displays significant decreasing trends during the early, mid and late rainfall seasons, with a 22% decline in flow for the mid rainfall season over the period 1944 to 2008 (Fig. 35), which corresponded to the rainfall changes observed at both the stations. Results consistently indicate that the correlation was strong between the river flow and the rainfall data at the Malabar stations (ranging from 0.46 to 0.49) (Table 9).

The rainfall at the Villiers station in the Vaal River catchment displayed a significant decreasing trend for all three seasons and the rainfall at the Mistley station in the Mgeni River catchment displayed a significant decreasing trend during the late rainfall season. The late season rainfall trends decreased the most, with a 25% and 37% decline at the Klerksdorp and Villiers stations respectively, over the interior of the Vaal River catchment, but only the Villiers station data display significant decreasing trends (Table 7). The present study also found that seasonal trends were insignificant at the majority of rainfall stations in southern Africa.

Of the catchments studied, the Tugela River indicates the greatest long-term (1927 to 2007) decline in flow of 73% during the early rainfall season (Table 8), followed by the Vaal River (69% decline during the early rainfall season). The Mgeni and Tugela Rivers displayed significant decreasing trends in seasonal flow at the 95% significance level, with the exception of the early rainfall season for the Mgeni at Table mountain gauge. The decline in the Tugela River flow is possibly due to the Tugela Transfer Scheme, because large volumes of water are transferred from the Tugela River to the Vaal River. Although the Orange River flow, which represents the central interior of South Africa, displays an increasing trend during all 3 seasons,

these were not significant at the 95% significance level.

7 3

y = 0 . 4 x + 7 3 . 4 5

= 0 . 4

p = 0 . 5 6

y = 0 . 4 2 x + 1 0 4

= 0 . 4 2

p = 0 . 8

y = 1 . 9 x + 6 2 . 4

= 1 . 9

= 0 . 7 2 p

Figure 33: Rainfall trends for the early, mid and late rainfall seasons at Malabar rainfall station in the Western Cape .

7 4

y = 0 . 0 8 7 x + 3 5 . 7

= 0 . 0 9

p = 0 . 7 8

y = 0 . 1 7 9 x + 5 4 . 6 2

= 0 1 8

p = 0 . 8 5

y = 0 . 2 1 4 x + 9 4 . 2

= 0 . 2 1

p = 0 . 8 3

Figure 34: Rainfall trends for the early, mid and late rainfall seasons at Touwsrivier rainfall

station in the Western Cape .

7 5

y = - 0 . 0 1 5 x + 2 . 3

= - 0 . 0 1 5

p = 0 . 9 9

y = - 0 . 0 4 1 x + 8 . 8 7

= - 0 . 0 4

p = 0 . 9 8

y = - 0 . 0 3 1 x + 7 . 7 2

= - 0 . 0 3

p = 0 . 9 8

Figure 35: Breede River flow trends during the early, mid and late rainfall seasons in the

Western Cape .

7 6 Table 7: Mann Kendall trend statistic results for the seasonal rainfall across South Africa and

Lesotho.

( A 9 5 %

S S N

e n e n o r m a l i z e d t y T r e n d R a i n f a l l R a i n f a l l

P r o b a b i l i R e g i o n

s B s Q

( ) ( )

t S t t t

t t T e a i i c i g n i f i c a n c e S t t

l o p e i n e r c e p a i o n e a o n

s s s

( Z ) )

l e v e l

l e r k s d o r p E

V a a l K a r l y - 0 . 0 4 0 . 5 2 N o t r e n d - 0 . 0 0 5 1 0 7 . 5 9

- 0 . 4 5 0 . 6 7 N o t r e n d - 0 . 1 6 0 2 8 9 . 4 3 d

M i

L a t e - 1 . 4 5 0 . 9 3 N o t r e n d - 0 . 4 0 1 1 4 6 . 4 1

a r l y l o e m h o f - 0 . 4 1 0 . 6 6 N o t r e n d - 0 . 1 3 0 9 9 . 3 6

- 0 . 2 7 0 . 6 1 N o t r e n d - 0 . 1 3 9 2 3 4 . 3 4 d

M i

L a t e - 0 . 3 3 0 . 6 3 N o t r e n d - 0 . 0 9 1 1 1 2 . 2 9

E e c r e a s n g

V l l e r s a r l y - 2 . 8 7 1 . 0 0 D i - 0 . 7 0 0 2 0 2 . 2 6

i i

e c r e a s n g

- 1 . 6 0 . 9 5 D i - 0 . 5 8 0 3 1 5 . 4 5 d

M i

e c r e a s n g

L a t e - 3 . 6 7 1 . 0 0 D i - 0 . 7 1 1 1 3 6 . 4 1

O r a n g e L l l e a r l y - 0 . 4 6 0 . 6 8 N o t r e n d - 0 . 2 2 4 1 3 2 . 5 1

d 0 . 7 4 0 . 7 7 N o t r e n d 0 . 4 6 7 2 6 2 . 0 5

M i

L a t e 0 . 5 7 0 . 7 2 N o t r e n d 0 . 1 5 3 1 3 8 . 4 9

a r l y d d e l p l a a t s 0 . 0 8 0 . 5 3 N o t r e n d 0 . 0 1 9 1 0 7 . 7 6

M i

d 0 . 3 1 0 . 6 2 N o t r e n d 0 . 1 3 7 2 2 7 . 0 6

M i

L a t e - 1 . 1 8 0 . 8 8 N o t r e n d - 0 . 3 0 7 1 4 5 . 4 2

a s t r o n a r l y 0 . 4 6 0 . 6 8 N o t r e n d 0 . 0 9 7 1 1 4 . 3 0

d - 0 . 6 5 0 . 7 4 N o t r e n d - 0 . 2 5 3 2 9 2 . 4 6

M i

L a t e - 1 . 0 5 0 . 8 5 N o t r e n d - 0 . 3 1 9 1 5 3 . 1 7

L e s o t h o T h a b a T s e k a a r l y 2 . 2 1 0 . 9 9 I n c r e a s n g 2 . 0 2 5 1 1 1 . 2 5

d 0 . 6 1 0 . 7 3 N o t r e n d 0 . 9 6 2 2 4 6 . 3 7

M i

L a t e 1 . 1 6 0 . 8 8 N o t r e n d 0 . 9 2 9 8 3 . 0 0

S e m o n k o n g a r l y 0 . 8 4 0 . 8 0 N o t r e n d 0 . 7 8 6 1 2 5 . 8 5

d 0 . 9 1 0 . 8 2 N o t r e n d 1 . 5 2 8 2 2 4 . 6 5

M i

L a t e - 0 . 7 8 0 . 7 8 N o t r e n d - 0 . 6 7 3 1 3 3 . 7 9

g e n s t l e y - 1 . 2 1 0 . 8 9 N o t r e n d - 0 . 4 5 2 2 0 9 . 1 4 a r l y

M i M i

d - 1 . 0 3 0 . 8 5 N o t r e n d - 0 . 7 2 5 3 7 9 . 4 4

M i

e c r e a s n g

L a t e - 1 . 8 0 0 . 9 6 D i - 0 . 7 7 7 1 7 3 . 7 9

a r l y N e w H a n o v e r 1 . 2 8 0 . 9 0 N o t r e n d 0 . 5 5 5 1 6 7 . 1 3

d 0 . 6 7 0 . 7 5 N o t r e n d 0 . 4 4 6 3 6 3 . 3 8

M i

L a t e 0 . 1 7 0 . 5 7 N o t r e n d 0 . 0 7 6 1 5 3 . 7 1

T u g e l a o o r s d e a r l y 0 . 0 9 0 . 5 4 N o t r e n d 0 . 0 2 4 1 7 6 . 0 5

M i

d - 1 . 0 6 0 . 8 6 N o t r e n d - 0 . 4 1 9 2 9 6 . 8 9

M i

L a t e - 0 . 3 1 0 . 6 2 N o t r e n d - 0 . 0 8 6 1 4 0 . 5 4

S w a r t w a t e r a r l y - 0 . 7 7 0 . 7 8 N o t r e n d - 0 . 3 9 0 1 9 5 . 2 1

d - 0 . 5 6 0 . 7 1 N o t r e n d - 0 . 3 6 4 3 4 3 . 0 6

M i

L a t e - 0 . 3 6 0 . 6 4 N o t r e n d - 0 . 0 7 9 1 2 0 . 4 6

T u g e l a F e r r y a r l y 1 . 7 8 0 . 9 6 I n c r e a s n g 0 . 4 6 6 1 0 5 . 9 9

d 1 . 2 9 0 . 9 0 N o t r e n d 0 . 5 8 3 2 4 8 . 7 9

M i

L a t e 0 . 0 3 0 . 5 1 N o t r e n d 0 . 0 0 4 1 0 3 . 2 2

r e e d e T o u w s r v e r a r l y 0 . 7 8 0 . 7 8 N o t r e n d 0 . 0 8 7 3 5 . 7 0

B i i

d 1 . 0 3 0 . 8 5 N o t r e n d 0 . 1 7 9 5 4 . 6 2

M i

L a t e 0 . 9 5 0 . 8 3 N o t r e n d 0 . 2 1 4 9 4 . 2 0

a l a b a r a r l y 0 . 1 4 0 . 5 6 N o t r e n d 0 . 0 4 1 7 3 . 4 5

d 0 . 8 3 0 . 8 0 N o t r e n d 0 . 4 1 9 1 0 4 . 8 1

M i

L a t e 0 . 5 9 0 . 7 2 N o t r e n d 0 . 1 9 0 6 2 . 4 2

7 7

Table 8: Mann Kendall trend statistic results for the seasonal river flow across South Africa.

( A 9 5 %

S S N t y

e n e n R a i n f a l l o r m a l i z e d P r o b a b i l i T r e n d i g n i f i c a n c e R i v e r f l o w

s B s Q s

( ( ) ) )

t t S t t t

i n e r c e p l o p e a i o n e a o n T e l e v e l

s s s s

( Z )

S t t t

a i i c

V a a l a r l y - 4 . 4 4 1 . 0 0 0 0 e c r e a s n g - 0 . 3 0 3 3 5 . 8 5

D i

d - 3 . 4 7 0 . 9 9 9 7 e c r e a s n g - 0 . 7 7 3 8 3 . 0 1

M i D i

L a t e - 3 . 2 9 0 . 9 9 9 5 e c r e a s n g - 0 . 6 2 8 6 7 . 0 1

D i

O r a n g e a r l y 0 . 1 7 0 . 5 6 8 9 N o t r e n d 0 . 0 5 8 1 0 4 . 1 9

d 0 . 8 4 0 . 7 9 8 4 N o t r e n d 0 . 4 2 9 1 6 3 . 8 8

M i

L a t e 0 . 4 4 0 . 6 6 9 0 N o t r e n d 0 . 2 2 2 1 5 4 . 4 1

T u g e l a a r l y - 3 . 4 2 0 . 9 9 9 7 e c r e a s n g - 0 . 6 2 4 8 0 . 2 9

D i

d - 2 . 0 5 0 . 9 7 9 9 e c r e a s n g - 0 . 8 3 6 1 9 2 . 9 7

M i D i

L a t e - 2 . 7 7 0 . 9 9 7 2 e c r e a s n g - 0 . 8 3 5 1 4 0 . 6 5

D i

- 0 . 8 9 0 . 8 1 2 1 - 0 . 0 1 7 6 . 8 8

g e n a r l y N o t r e n d

M i

- 3 . 6 2 0 . 9 9 9 9 - 0 . 2 5 1 2 1 . 4 9

d e c r e a s n g

M i D i

- 1 . 3 9 0 . 9 1 7 5 - 0 . 1 0 5 1 5 . 1 2

L a t e N o t r e n d

r e e d e a r l y - 2 . 6 3 0 . 9 9 5 8 e c r e a s n g - 0 . 0 1 5 2 . 3 0

B D i

d - 2 . 0 7 0 . 9 8 0 6 e c r e a s n g - 0 . 0 4 1 8 . 8 7

M i D i

L a t e - 2 . 0 2 0 . 9 7 8 4 e c r e a s n g - 0 . 0 3 1 7 . 7 2

D i

7 8 Table 9: Kendall tau correlation coefficients for river flow and rainfall at stations during different

rainfall seasons.

i g n i f i c a n c e S t t t

R a i n f a l l e a o n R i v e r R a i n f a l l a i o n K e n d a l l a u V a l i d c a e

s s s s

a r l y r e e R v e r f l o w T o u w s r v e r 0 . 3 2 8 6

B i i i 0 . 0 0 0 0

r e e R v e r f l o w a l a b a r 0 . 4 9 6 5

B i M 0 . 0 0 0 0

d r e e R v e r f l o w T o u w s r v e r 0 . 3 6 8 6 0 . 0 0 0 0

M i B i i i

r e e R v e r f l o w a l a b a r 0 . 4 4 6 5 0 . 0 0 0 0

B i M

L a t e r e e R v e r f l o w T o u w s r v e r 0 . 3 5 8 6

B i i i 0 . 0 0 0 0

r e e R v e r f l o w a l a b a r 0 . 4 6 6 5

B i M 0 . 0 0 0 0

a r l y g e n R v e r f l o w s t l e y 0 . 1 4 5 7 0 . 0 6

M i i M i

g e n R v e r f l o w N e w H a n o v e r 0 . 1 7 5 8 0 . 0 3

M i i

d g e n R v e r f l o w s t l e y 0 . 0 9 5 7 0 . 1 7

M i M i i M i

g e n R v e r f l o w N e w H a n o v e r 0 . 3 5 8 0 . 0 0 0 3

M i i

L a t e g e n R v e r f l o w s t l e y - 0 . 1 5 5 7 0 . 0 4

M i i M i

g e n R v e r f l o w N e w H a n o v e r 0 . 2 9 5 8 0 . 0 0 0 7

M i i

a r l y O r a n g e R v e r f l o w a s t r o n 0 . 4 8 9 5 0 . 0 0 0 0

i Z

O r a n g e R v e r f l o w d d e l p l a a t s 0 . 4 1 9 5 0 . 0 0 0 0

i M i

O r a n g e R v e r f l o w L l l e 0 . 5 5 7 7

i i 0 . 0 0 0 0

d O r a n g e R v e r f l o w a s t r o n 0 . 6 9 5

M i i Z 0 . 0 0 0 0

O r a n g e R v e r f l o w d d e l p l a a t s 0 . 5 5 9 5 0 . 0 0 0 0

i M i

O r a n g e R v e r f l o w L l l e 0 . 5 6 7 7 0 . 0 0 0 0

i i

L a t e O r a n g e R v e r f l o w a s t r o n 0 . 4 9 9 5

i Z 0 . 0 0 0 0

O r a n g e R v e r f l o w d d e l p l a a t s 0 . 5 2 9 5

i M i 0 . 0 0 0 0

O r a n g e R v e r f l o w L l l e 0 . 4 9 7 7 0 . 0 0 0 0

i i

a r l y T u g e l a R v e r F l o w o o r s d e 0 . 2 2 8 1 0 . 0 0 1

i M i

T u g e l a R v e r F l o w S w a r t w a t e r 0 . 3 7 7 6

i 0 . 0 0 0 0

T u g e l a R v e r F l o w T u g e l a F e r r y 0 . 1 5 8 1 0 . 0 1 9

d T u g e l a R v e r F l o w o o r s d e 0 . 4 1 8 1 0 . 0 0 0 0

M i i M i

T u g e l a R v e r F l o w S w a r t w a t e r 0 . 2 9 7 6 0 . 0 0 0 1

T u g e l a R v e r F l o w T u g e l a F e r r y 0 . 0 3 8 1

i 0 . 0 0 0 0

L a t e T u g e l a R v e r F l o w o o r s d e 0 . 3 5 8 1 0 . 0 0 0 0

i M i

T u g e l a R v e r F l o w S w a r t w a t e r 0 . 3 7 6 0 . 0 0 0 0

T u g e l a R v e r F l o w T u g e l a F e r r y 0 . 2 4 8 1 0 . 0 0 0 8

a r l y V a a l R v e r F l o w l o e m h o f 0 . 0 8 6 5 0 . 1 7

i B

V a a l R v e r F l o w l e r k s d o r p 0 . 0 7 6 9 0 . 1 8

i K

V a a l R v e r F l o w V l l e r s 0 . 1 8 6 7 0 . 0 1 4

i i i

d V a a l R v e r F l o w l o e m h o f 0 . 3 6 9

M i i B 0 . 0 0 0 0

V a a l R v e r F l o w l e r k s d o r p 0 . 1 2 6 9 0 . 0 6

i K

V a a l R v e r F l o w V l l e r s 0 . 1 9 6 7 0 . 0 1

i i i

L a t e V a a l R v e r F l o w l o e m h o f 0 . 2 6 9 0 . 0 0 5

i B

V a a l R v e r F l o w l e r k s d o r p 0 . 2 8 6 9 0 . 0 0 2

i K

V a a l R v e r F l o w V l l e r s 0 . 3 6 7 0 . 0 0 0 1 4

i i i

7 9