Albertus Jacobus Smit

Extreme heat and humidity are increasing globally, with direct implications for heat-related mortality. This study examined associations between daily natural-death counts and heat exposure in the five district municipalities of Limpopo Province, South Africa, where isolated surges in excess deaths were detected by mortality surveillance in November 2023 and December 2024. We combined spatially averaged district-level meteorological observations from 1 January 1991 to 20 July 2025 with daily mortality data from 1 January 2022 to 10 May 2025 and analysed the Excess Heat Factor (EHF) and apparent temperature (AT) in calendar-matched case-crossover models of observed death counts for all ages and ages 60 yrs and older. EHF entered the models as its positive part in local severity units. The analysis showed that absolute humidity, maximum temperature, minimum temperature and diurnal temperature range increased across districts, with the fastest proportional increases in the extreme exposure categories. At provincial level, for all ages, each severity unit of lag 0–1 EHF was associated with a mortality rate ratio of 1.191 (95% confidence interval, CI: 1.168–1.214) and extreme heatwave days carried rate ratios of 1.830 (95% CI: 1.652–2.027). Each interquartile-range increase in AT was associated with rate ratios of 1.074 (95% CI: 1.061–1.088). The EHF–mortality association was present in every district and heterogeneous in magnitude ranging from 1.092 (1.036–1.151) to 1.231 (1.169–1.296) across the districts, whereas the AT association was small and spatially uniform once EHF was included in the model. For both EHF and AT (and combined), the association with mortality was ubiquitously amplified in all models, in all districts for the 60-yrs-and-older age class. A proposed EHF-based warning was tested retrospectively and showed that both mortality surges were preceded by “warning-level” EHF alerts in every district. A district-specific, severity-based EHF alert scheme, evaluated here against the 2022–2025 mortality series, could improve municipal heat-health warning systems in Limpopo and provides a template for similar analyses elsewhere in South Africa.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.

Satellite sea-surface-temperature (SST) upwelling indices usually contrast coastal temperature with a fixed offshore reference, although the offshore extent of the surface cool tongue varies across cells and days. We replace the fixed reference with a daily fitted thermal breakpoint from a continuous two-segment regression on cross-shore SST profiles, accepted only when model-evidence, slope-ratio, offshore-baseline, edge-buffer, and residual-autocorrelation criteria are met. We apply the method to five Benguela upwelling cells (UCs) from 2015 to 2025 using two fine-resolution Level-4 SST products, namely the Operational Sea Surface Temperature and Ice Analysis and the Geo-Polar Blended analysis from the US National Oceanic and Atmospheric Administration; coarser Advanced Very High Resolution Radiometer and microwave optimum interpolation products serve as resolution comparisons. Median fitted breakpoints span 114 to 270 km across UCs, so 50 to 100 km reference points usually sample inside the fitted inshore segment rather than offshore water. In the Operational Sea Surface Temperature and Ice Analysis product, the daily correlation between inshore-segment SST drawdown and the conventional fixed-distance contrast rises from r = 0.06 at 50 km to r = 0.93 at 500 km, showing that reference distance changes the diagnostic itself. The Lüderitz annual r₅₀ point estimate is negative (-0.16), but its block-bootstrap interval includes zero. A paired comparison with a Bakun-type offshore-Ekman-transport flag shows that southern Benguela cells retain SST structure without the local wind flag on ca. one fifth of matched days. The method therefore positions fixed-reference SST indices as structural surface-temperature indicators whose interpretation depends on cell-scale geometry and SST-wind co-activity.