Dangerous heat in dense settlements in a tropical African city

With ongoing climate change and rapid urbanization, exposure to severe heat is expected to accelerate in tropical East African cities. Yet not all parts of the city are equally vulnerable. The present-day intra-urban heat stress variation in Kampala, the capital city of Uganda, is quantified by deriving the daily mean, minimum and maximum Humidex Index from a network of low-cost temperature and humidity sensors operational in 2018-2019. Heat is shown to be heterogeneously distributed over the city, with a daily maximum intra-urban Humidex Index deviation of 6.4°C averaged over the observational period, but reaching 14.5°C on the most extreme day.

Also extreme heat is heterogeneously distributed over the city, putting local populations at risk of great discomfort or health danger. One station in a dense settlement reports a daily maximum Humidex Index above 40°C in 68% of the observation days, a level which was never reached at the nearby campus of the Makerere University, and only a few times at the city outskirts. About 75% of this intra-urban heat stress variability is explained by the Normalized Difference Vegetation Index (NDVI), though strong collinearity is found with other variables like impervious surface fraction and population density.

Overall, our results highlight the importance of (i) including both temperature and humidity in heat stress studies, (ii) urban greening in city planning, and (iii) large intra-urban heat stress variations in heat action planning in tropical humid cities.