Key Points

• A heat wave hit France at the end of week 26/2025 and continued into week 27/2025. In Brittany, the heat wave began on Saturday, June 28, when Météo France issued a yellow heat wave alert for Ille-et-Vilaine (home to 32.3% of the region’s resident population). On Sunday, June 29, Monday, June 30, and Tuesday, July 1, Ille-et-Vilaine was placed under an orange alert and Morbihan under a yellow alert (22.5% of the regional resident population). On Wednesday, July 2, all Breton departments returned to a green alert.

• A regional analysis of emergency care utilization indicates an increase in the iCanicule composite health indicator (covering hyperthermia, dehydration, and hyponatremia) during the heatwave period.

This trend falls within the expected fluctuations for the meteorological conditions and is observable across the region as a whole, particularly in Ille-et-Vilaine and Finistère (a department that remained at green alert).