Historical and projected trends in near-surface temperature indices for 22 locations in South Africa

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.

Temperature and relative humidity trends in the northernmost region of South Africa, 1950–2016

“…13 analysed spatial and temporal historical climate observations in southern Africa to validate simulation models for projecting climate trends. Kruger et al48 investigated historical trends in near-surface minimum and maximum temperatures, as well as extreme temperature indices in South Africa. This was achieved through critically comparing quality-controlled station observations with downscaled model projections, so as to provide valuable information concerning the interpretation of model-generated projections.…”

“…This was achieved through critically comparing quality-controlled station observations with downscaled model projections, so as to provide valuable information concerning the interpretation of model-generated projections. Kruger et al's48 results demonstrate that model outputs tend to simulate the historical trends accurately for annual means of daily maximum and minimum temperatures, but have limitations when assessing temperature extremes. For correctly estimating the potential impact of climate change in a given region, particularly for sectors such as agriculture, it is necessary to reconcile climate observations and model projections.…”

Trend analysis of cold extremes in South Africa: 1960–2016

“…Future trends indicate that cold spells are projected to be quite spatially variable across South Africa, which is heightened with the use of some indices (Kruger et al ., 2019). However, decreases are more pronounced in the central and northern parts of the country (Kruger et al ., 2019, which to a certain extent agree with the findings of this study.…”

“…Alexander et al ., 2006; Perkins‐Kirkpatrick et al ., 2017). Most recent studies in South Africa examined both warm and cold extremes using the ETCCDI indices and found a general decrease in extreme cold events based upon temperature data from the South African Weather Service (SAWS) between the periods; 1961–2000 (New et al ., 2006), 1962–2009 (Kruger and Sekele, 2013), 1960–2010 (Mackellar et al ., 2014), 1931–2015 (Kruger and Nxumalo, 2017) and 1951–2005 (Kruger et al ., 2019). New et al .…”

“…Kruger et al . (2019) focussed predominantly on projected extreme temperature trends. In addition, these studies failed to examine threshold and percentile‐based indices on a seasonal timescale with a specific focus on extreme cold temperature events, which are important to many sectors in particularly agricultural.…”