Diurnal Variation of Wet Bulb Globe Temperature and Heat Stress Risk During the Wet Season in Port Harcourt, Nigeria

Daso; I.A.; Iyama; W.A.; Gobo; A.E.; Corresponding Author

doi:10.56201/ijgem.vol.12.no10.2026.pg369.380

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Diurnal Variation of Wet Bulb Globe Temperature and Heat Stress Risk During the Wet Season in Port Harcourt, Nigeria

Daso, I.A., Iyama, W.A. , Gobo, A.E., Corresponding Author

Abstract

This study examined the diurnal variation of Wet Bulb Globe Temperature and associated heat stress risk during the wet season in Port Harcourt Metropolis, Rivers State, Nigeria. Hourly WBGT measurements were taken at eight purposively selected sites representing three land use types (urban, peri-urban, and rural) during three representative time blocks (morning: 06:00–09:00, afternoon: 12:00–15:00, and evening: 18:00–21:00) over three non-consecutive days per site between June and August 2026. WBGT was measured using the Heat Index WBGT Meter Model WBGT-2010SD, while supporting meteorological variables were measured using the PCE-FWS 20N mobile weather station. Heat stress risk was classified using three indices: WBGT (ISO 7243), Heat Index (US NWS), and Temperature- Humidity Index . Results showed that WBGT ranged from 23.0°C in rural areas to 34.4°C in the urban core. The diurnal pattern was sinusoidal, with a minimum of 24.2°C at 06:00 and a maximum of 32.7°C at 13:00. The peak rate of increase (2.3°C/hour) occurred between 07:00 and 09:00, and WBGT exceeded 30.0°C for seven consecutive hours (09:00–15:00). Extreme heat stress risk (WBGT ≥ 32.0°C) occurred for three hours (12:00–14:00). All three indices identified the early afternoon as the period of greatest heat stress. The study concludes that heat stress is a significant hazard during the wet season in Port Harcourt, particularly during the early afternoon. The findings provide the first systematic, hourly WBGT dataset for the city and offer an empirical basis for occupational health policies, public health advisories, and climate change adaptation strategies. To address the findings of the study, the study recommended that outdoor work should be scheduled to avoid the peak heat stress period between 09:00 and 15:00; heat advisories should be issued during the early afternoon, when WBGT is highest; environmental regulatory agencies, develop heat-health action plans, workplace heat regulations, and climate adaptation strategies; and continuous 24-hour WBGT monitoring should be carried out to capture night-time conditions.

Keywords

Wet Bulb Globe Temperaturediurnal variationheat stresswet seasonPort Harcourtheat indexoccupational health

References

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Diurnal Variation of Wet Bulb Globe Temperature and Heat Stress Risk During the Wet Season in Port Harcourt, Nigeria

Abstract

Keywords

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