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.
Highlights
BackgroundGlobal warming, as a result of increased concentrations of greenhouse gases (GHGs), poses a considerable risk to a sustainable present climate regime
The simulations of nine coupled Atmosphere-Ocean General Circulation Models (AOGCMs), which were included in the Inter-Governmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5)[10], were used as inputs for a 1951–2095 simulation downscaled to a resolution of 0.4° x 0.4° using the Rossby Centre Regional Model Version 4 (RCA4) regional climate model (RCM)[11]
We aim to provide insight into systematic biases or errors between CORDEX model simulated and observed daily maximum and minimum temperatures at 22 locations in South Africa, over the period 1951–2005
Summary
As a result of increased concentrations of greenhouse gases (GHGs), poses a considerable risk to a sustainable present climate regime In this context, a number of studies have previously been conducted to investigate historical trends in near-surface temperatures in South Africa, including extremes.[1,2,3,4] Most of these studies agree – indicating a general, but spatially variable, warming over recent decades. The main parts of the publication considered in this study are future projections of the average near-surface temperature for two 30-year periods, i.e. 2036–2065 and 2066–2095
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