Escalating Heatwave Activity and Return Periods Across the Climatic Zones of Ghana

Edmund. I Yamba, Daniel Amponsah , Nana Ofosuhene Pinkrah , Stephen Oppong, Cosmos Senyo Wemegah, Mary Jessie Adjei, Alex Kwao Ablerdu 

Heatwaves are an increasing public health concern in West Africa, yet their characteristics and recurrence across Ghana’s climatic zones remain poorly quantified. Previous assessments in Ghana have largely focused on individual cities and percentile-based thresholds, which characterize extremes relative to the local climatology but do not explicitly account for recently experienced thermal conditions. Here, we assess the characteristics and return periods of heatwaves across Ghana’s climatic zones using the Excess Heat Factor (EHF) framework. We analyzed quality-controlled daily maximum and minimum temperatures from 24 Ghana Meteorological Agency synoptic stations spanning 1960–2022. Heatwaves were defined as at least three consecutive days with EHF > 0 and characterized in terms of occurrence, frequency, duration, and intensity. Return levels of heatwave intensity and duration were estimated for 2–50-year return periods using Peaks-Over-Threshold modelling with the Generalized Pareto distribution. All climatic zones exhibited significant warming, transitioning from predominantly cooler conditions in the 1960s–1970s to sustained warming from the mid-1980s, with minimum temperatures increasing more rapidly than maximum temperatures in most zones and reducing nocturnal thermal relief. Heatwave activity increased markedly thereafter, with total heatwave days increasing significantly across all zones (p < 0.001) and fastest in the Coastal (0.70 days year−1) and Forest (0.54

days year−1) zones. Heatwave episodes were concentrated mainly between February and April. Heatwave intensity generally increased northward, whereas duration increased southward, and this contrast became more pronounced toward longer return periods. At the 50-year return period, the Sudan Savannah exhibited a high-intensity but comparatively short heatwave return level (≈12.5 °C2; ≈21 days), whereas the Coastal zone exhibited substantially lower intensity but greater persistence (≈3.5 °C2; ≈39 days), although uncertainty increased at longer return periods. These findings demonstrate that heatwave hazard in Ghana is intensifying but spatially differentiated, with rare events characterized predominantly by intensity in the north and persistence in the south. The results provide a quantitative climatological basis for developing climate-zone-specific heatwave monitoring and, with appropriate impact-based validation, a national heat-health early-warning framework for Ghana.