Long-term changes in the climate extremes and their impacts on maize yields in the summer rainfall region of South Africa

Abstract This study analysed spatio-temporal trends of selected extreme climate indices during the maize-growing season and quantified their contributions to maize yield variability across key maize-producing districts in South Africa. Daily climate data from representative stations across contrasting agroecological zones were analysed, together with district-level maize yield records, using Sen’s slope, the Mann–Kendall test, Pearson correlation coefficient ( $$\:r$$ ), and stepwise multiple regression. Results reveal significant warming across the summer rainfall region of South Africa. Mean seasonal air temperature (TMm) increased from 0.02 °C per annum at wetter stations (Lydenburg) to 0.06 °C per annum at semi-arid stations (Klerksdorp and Vryburg), while maximum daytime air temperature (TXx) increased by 0.05–0.11 °C per annum. The frequency of very hot days (TX90p) increased by 0.19–0.50% per annum, whereas the frequency of extreme cold days (TX10p) declined by − 0.10 to − 0.29% per annum, indicating a clear shift toward warmer growing-season conditions. Inconstrast, total seasonal rainfall exhibited highly variable and statistically non-significant trends across all stations. Rainfall frequency decreased more strongly in semi-arid districts (− 0.56 to − 1.16 days per annum), while moisture availability represented by the Standardized Precipitation Evapotranspiration Index (SPEI) declined in drier regions (− 0.03 to − 0.05 per annum). These findings indicate that rising air temperatures, more frequent heat extremes, declining rainfall frequency, and reduced moisture availability are the predominant climate-related risks in major maize-growing regions. Maize yield showed negative correlations with TX90p ( $$\:r$$ = −0.46 to − 0.62) and positive correlations with SPEI ( $$\:r$$ = 0.68–0.76). Climate variability explained up to 69% of the interannual variability in maize yield in water-limited regions, indicating that increasing heat extremes and declining moisture availability were key drivers of maize yield fluctuations. These findings highlight the need for locally tailored adaptation strategies to enhance the resilience of maize production in South Africa.