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

Abstract

Extreme cold events (“cold waves”) have disastrous impacts on ecosystem and human health. Evidence shows that these events will still occur under current increasing mean temperatures. Little research has been done on extreme cold events, especially in developing countries such as South Africa. These events pose a significant threat due to the low adaptive capacity, urgent development needs and relatively inadequate infrastructure in South Africa. This study presents annual and seasonal, spatial and temporal trend analyses of extreme cold temperature events for the period 1960–2016. We apply the World Meteorological Organisation Commission for Climatology and Indices Expert Team on Sector‐Specific Climate Indices (ET‐SCI) to South Africa for the first time, with comparison to the World Meteorological Organisation Expert Team on Climate Change Detection (ETCCDI) indices previously used in South Africa. The extreme cold indices are calculated using the RClimDex and ClimPACT, respectively. Trends were calculated using the non‐parametric Mann‐Kendall test, Spearman Rank Correlation Coefficient and Sen's slope estimates. A decreasing trend is found for annual cold spell duration and cold wave frequency, at rates of 0.10 days.day−1 and 0.02 events.day−1, respectively. Seasonally, coldest day temperatures increased in autumn, with increases of 0.02°C.day−1 for the period 1960–2016. Regionally, increasing trends in annual cold spell duration days were evident in stations located in the Western Cape, Eastern Cape, North‐West Province, at a rate of 0.03 days.day−1. Increasing trends in cold waves were observed for stations in Northern Cape, Gauteng, KwaZulu‐Natal and the Eastern Cape Province, at a rate of 0.01 events.day−1. These results contribute to the awareness and recognition of the incidence and duration of cold extreme events in South Africa, seeing that studies suggest that anomalously cold events may persist in a warming world.

Detecting Extreme Temperature Events Using Gaussian Mixture Models

“…GMM are a promising method for calculating the return periods of extreme events, and additionally determining the shape of the entire distribution for daily maximum temperature data. Some studies used seasonal periods to analyse extreme events (Walt & Fitchett, 2021 -19-manuscript submitted to JGR: Atmospheres dicted to change with climate change (Wang et al, 2021). Therefore, the definition of current seasonal periods will not necessarily be valid for future climates.…”

Spatiotemporal characteristics of human thermal comfort across southern Africa: An analysis of the Universal Thermal Climate Index for 1971–2021

“…Increasing heat stress occurrences, especially during the day‐time, relate to increasing trends observed for the incidence and intensity of hot ETEs, and together with projections indicating, with high confidence, that southern Africa will experience an increased frequency and intensity of hot ETEs, this suggests an increased risk of additional very strong and extreme heat stress incidences in coming years (Mbokodo et al ., 2020; Engelbrecht and Monteiro, 2021; Iyakaremye et al ., 2021; van der Walt and Fitchett, 2021a; Meque et al ., 2022). Decreasing cold stress occurrences, especially during the night‐time, relate to declines thereof for cold ETEs (van der Walt and Fitchett, 2021b). Considering human health, both results have negative implications.…”

“…Far less research has been conducted on extreme thermal (temperature) events, and much of that literature focuses on more simplistic indices of temperature alone (Harrington and Otto, 2020; van der Walt and Fitchett, 2022). This is problematic because anomalous heat or cold events over long periods can lead to thermal discomfort and heat or cold stress (van der Walt and Fitchett, 2021a, 2021b, 2022). This can result in heat‐ or cold‐related illnesses, including cardiovascular diseases, strokes, severe headaches, damage to the brain, heart, lungs, and kidneys, decreased metabolic activity, and in severe cases mortality (Scott, 2015; Smith and Sheridan, 2018; van der Walt and Fitchett, 2021a; 2021b; 2022).…”

“…This is problematic because anomalous heat or cold events over long periods can lead to thermal discomfort and heat or cold stress (van der Walt and Fitchett, 2021a, 2021b, 2022). This can result in heat‐ or cold‐related illnesses, including cardiovascular diseases, strokes, severe headaches, damage to the brain, heart, lungs, and kidneys, decreased metabolic activity, and in severe cases mortality (Scott, 2015; Smith and Sheridan, 2018; van der Walt and Fitchett, 2021a; 2021b; 2022). Furthermore, underlying and pre‐existing medical conditions (e.g., asthma, hypertension, diabetes, cardiovascular diseases) are exacerbated by extreme heat and cold exposure (Scott, 2015; Smith and Sheridan, 2018; Ncongwane et al ., 2021).…”

“…Across southern Africa, temperatures are increasing substantially compared to global trends (Engelbrecht et al ., 2015; Masson‐Delmotte et al ., 2021). This is reflected in the regions observed warm ETE trends which are increasing in incidence and intensity, whereas decreasing trends are observed for cold ETEs (New et al ., 2006; Kruger and Nxumalo, 2017; Kruger et al ., 2019; van der Walt and Fitchett, 2021a; 2021b). While these trends are indicative of thermal comfort changes across southern Africa, studies exploring ETE trends have only considered threshold‐ or percentile‐based indices of temperature, without consideration of a wider range of meteorological parameters (e.g., wind speed and humidity), known to influence thermal comfort (Błażejczyk et al ., 2013; Di Napoli et al ., 2018).…”