Europe is heading into its fourth heatwave of the summer as high-pressure systems funnel hot air north from the Mediterranean. Meteorological agencies forecast 34 °C in parts of England on Tuesday, while French forecasters expect temperatures near 40 °C in Lyon and across much of the south. Forty-two French departments are already on orange heat alert, due to expand to 46, and the UK Health Security Agency has issued a yellow heat-health warning from Monday through mid-week. The extreme heat is straining critical infrastructure. River temperatures and low water levels have forced several European nuclear reactors to reduce output or shut temporarily, industry analysts say, leaving utilities to burn more natural gas at a time when inventories are being built for winter. Researchers at ETH Zurich warn that current climate conditions could allow rolling heat and drought events lasting weeks, with temperatures of up to 45 °C, heightening risks to energy supplies, agriculture and public health. Water and health authorities are taking emergency measures. South East Water urged customers in Sussex to restrict usage as reservoirs hit their lowest August levels since the 2022 drought, adding to hosepipe bans that already cover about 8.5 million UK households. Care-home operators in France and local governments across Belgium and the UK are opening cooling centres and reinforcing hydration campaigns for vulnerable residents.