Identification and characterization of 2024 Heat waves in Burkina Faso.

The West African Sahel has suffered an unprecedented hot season in the first half of 2024. This preliminary observational study characterises this extreme heat in the urban context of Ouagadougou, one of the major cities in the region where significant death casualty was reported. Using data from the national meteorological agency and the European reanalysis (ERA5), the study investigated both the daytime (Tmax) and nighttime temperatures (Tmin) with the 1991-2020 as reference period. The results show that the average monthly Tmax anomaly ranged from 1.42 °C in January 2024 to 2.41 °C in June 2024, versus -0.4 °C in  January 2024 and 2.05 °C in June 2024 for Tmin, showing that the heat was more important in 2024 than in the historical period. Using the heat wave definition of the Burkina Faso Red Cross heat wave early action protocol, a total of four (one) daytime (nighttime) heat waves were recorded in the city between March and May. This is to be compared with a historical frequency of one event every four years. The longest daytime heat lasted six days with Tmax reaching a maximum of 44.5°C. The unique nighttime heat wave was twice as long as the longest daytime heat wave, persisting for 13 days between late April and early May, a record in the city. From a spatial perspective, the heat was not evenly distributed as some neighbourhoods were significantly hotter than the rest of the city. Furthermore, the initial findings of a household survey conducted in the city corroborated the unprecedentedness of the situation as most respondents reported having never experienced such heat levels in the past with considerable impacts on their health and livelihoods. These results underscore the need for more efforts towards heat wave risk management in African cities.