100
S. Kusangaya et al.
out that warm extremes increased while cold extremes decreased for South Africa.
Hulme et al. (2001) further established that temperatures were higher in the 1990s
than previously in the century and are currently between 0.2 and 0.3 °C warmer than
the 1961–1990 average. An increasing trend across the whole region, with particularly large rates of increase in Namibia and Angola has been identified. Overall, for
Southern Africa, minimum temperatures are rising faster than maximum temperatures and there is a notable decrease in cold extremes while warm event extremes are
on the increase.
An increase in temperature typically causes the intensification of the hydrological
cycle (Trenberth 1999; Allen and Ingram 2002; Schulze 2005; Huntington 2006;
Syed et al. 2010), as a result of the increase in turbulence and evaporation, as well
as rainfall (Warburton et al. 2005b). This potentially increases the frequency of
occurrence of droughts and floods (Schulze 2011) which may lead to changing rainfall
patterns and hence the spatial and temporal distribution of runoff, soil moisture
and ground water reserves. As such, temperature changes have a direct bearing on
water resources availability within Southern Africa. A summary of the analysis of
temperature changes over Southern Africa is given in Table 1.
3.2 Rainfall Changes in Southern Africa
Climate change detection studies on rainfall have been carried out using observed,
interpolated and remote sensing derived rainfall. Nicholson et al. (2017) found a
shift from relatively wet conditions of the 1920s–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
eighties is 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 20ºS, as well as
in Madagascar resulting in a shorter and weaker rainfall season in southern Africa
with rainfall in Angola, Zambia and Namibia tending to decrease from December to
March. New et al. (2006) reported that spatially coherent increases in consecutive dry
days were found over much of southern Africa in the past decades of the twentieth
century. However, analysis of historical rainfall trends for Zimbabwe (1933–2000)
by Mazvimavi (2010b) showed that there was no statistically significant rainfall
reduction in Zimbabwe. This, however, contrast sharply with earlier results from
Unganai (1996) who concluded that annual rainfall in Zimbabwe had declined by
10% between 1900 and 1994. Elsewhere, in South Africa, Hewitson and Crane (1996)
reported increase in rainfall in regions of South Africa where orographic influences
dominate based on 50 years of data (1950–1999). Increases in late summer dry-spell
duration for much of the summer rainfall region were also detected in the same study.
Combined results from rainfall trend analysis suggest that changes in rainfall are
contrasting and subject to considerable uncertainty, regarding the extent (spatial and
temporal) and magnitude of change. This is largely because rainfall is characterised
S. Kusangaya et al.
out that warm extremes increased while cold extremes decreased for South Africa.
Hulme et al. (2001) further established that temperatures were higher in the 1990s
than previously in the century and are currently between 0.2 and 0.3 °C warmer than
the 1961–1990 average. An increasing trend across the whole region, with particularly large rates of increase in Namibia and Angola has been identified. Overall, for
Southern Africa, minimum temperatures are rising faster than maximum temperatures and there is a notable decrease in cold extremes while warm event extremes are
on the increase.
An increase in temperature typically causes the intensification of the hydrological
cycle (Trenberth 1999; Allen and Ingram 2002; Schulze 2005; Huntington 2006;
Syed et al. 2010), as a result of the increase in turbulence and evaporation, as well
as rainfall (Warburton et al. 2005b). This potentially increases the frequency of
occurrence of droughts and floods (Schulze 2011) which may lead to changing rainfall
patterns and hence the spatial and temporal distribution of runoff, soil moisture
and ground water reserves. As such, temperature changes have a direct bearing on
water resources availability within Southern Africa. A summary of the analysis of
temperature changes over Southern Africa is given in Table 1.
3.2 Rainfall Changes in Southern Africa
Climate change detection studies on rainfall have been carried out using observed,
interpolated and remote sensing derived rainfall. Nicholson et al. (2017) found a
shift from relatively wet conditions of the 1920s–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
eighties is 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 20ºS, as well as
in Madagascar resulting in a shorter and weaker rainfall season in southern Africa
with rainfall in Angola, Zambia and Namibia tending to decrease from December to
March. New et al. (2006) reported that spatially coherent increases in consecutive dry
days were found over much of southern Africa in the past decades of the twentieth
century. However, analysis of historical rainfall trends for Zimbabwe (1933–2000)
by Mazvimavi (2010b) showed that there was no statistically significant rainfall
reduction in Zimbabwe. This, however, contrast sharply with earlier results from
Unganai (1996) who concluded that annual rainfall in Zimbabwe had declined by
10% between 1900 and 1994. Elsewhere, in South Africa, Hewitson and Crane (1996)
reported increase in rainfall in regions of South Africa where orographic influences
dominate based on 50 years of data (1950–1999). Increases in late summer dry-spell
duration for much of the summer rainfall region were also detected in the same study.
Combined results from rainfall trend analysis suggest that changes in rainfall are
contrasting and subject to considerable uncertainty, regarding the extent (spatial and
temporal) and magnitude of change. This is largely because rainfall is characterised