Abstract:
Motivated by the risks posed by global warming, historical trends and future projections of near-surface
temperature in South Africa have been investigated in a number of previous studies. These studies included
the assessment of trends in average temperatures as well as extremes. In this study, historical trends in
near-surface minimum and maximum temperatures as well as extreme temperature indices in South Africa
were critically investigated by comparing quality-controlled station observations with downscaled model
projections. Because climate models are the only means of generating future global warming projections,
this critical point comparison between observed and downscaled model simulated time series can provide
valuable information regarding the interpretation of model-generated projections. Over the historical
1951–2005 period, both observed data and downscaled model projections were compared at 22 point
locations in South Africa. An analysis of model projection trends was conducted over the period 2006–2095.
The results from the historical analysis show that model outputs tend to simulate the historical trends well
for annual means of daily maximum and minimum temperatures. However, noteworthy discrepancies exist
in the assessment of temperature extremes. While both the historical model simulations and observations
show a general warming trend in the extreme indices, the observational data show appreciably more spatial
and temporal variability. On the other hand, model projections for the period 2006–2095 show that for the
medium-to-low concentration Representative Concentration Pathway (RCP) 4.5, the projected decrease in
cold nights is not as strong as is the case for the historically observed trends. However, the upward trends in
warm nights for both the RCP4.5 and the high concentration RCP8.5 pathways are noticeably stronger than
the historically observed trends. For cool days, future projections are comparable to the historically observed
trends, but for hot days noticeably higher. Decreases in cold spells and increases in warm spells are expected
to continue in future, with relatively strong positive trends on a regional basis. It is shown that projected trends
are not expected to be constant into the future, in particular trends generated from the RCP8.5 pathway that
show a strong increase in warming towards the end of the projection period.
SIGNIFICANCE :
• Comparison between the observed and simulated trends emphasises the necessity to assess the
reliability of the output of climate models which have a bearing on the credibility of projections.
• The limitation of the models to adequately simulate the climate extremes, renders the projections
conservative, which is an important result in the light of climate change adaptation.
