Hitzewelle

Hitzewelle, or heatwave, is a period of unusually hot weather that lasts for several days or longer. It is characterized by temperatures well above the normal for the location and season, often accompanied by high night-time temperatures. Definitions vary by country and meteorological service, but a heatwave generally involves a sequence of above-average days, with thresholds differing across climates.

Causes include persistent high-pressure systems that trap heat in the atmosphere, a slow-moving or blocking weather pattern, and long-term warming trends from climate change that raise baseline temperatures and the probability of extreme heat. Urban areas can experience amplified effects due to the urban heat island effect, where built environments retain heat.

Impacts can be severe. Heatwaves increase the risk of heat-related illnesses and deaths, particularly among the elderly, children, and people with chronic illnesses. They can strain power grids, water supplies, and transportation; damage crops; exacerbate drought conditions; and raise the risk of wildfires. Night-time temperatures that remain high can hinder recovery from daytime heat and worsen health outcomes.

Forecasting and response: National meteorological services issue heat warnings based on region-specific thresholds. Public health authorities may activate heat-health action plans, open cooling centers, advise on hydration and reduced outdoor activity, and implement measures to protect vulnerable populations. Urban planning and building design—such as reflective surfaces, green spaces, and cooling infrastructure—aim to reduce heat exposure and improve resilience.

History: Notable heatwaves include the 2003 European event, the 2010 Russian heatwave, and episodes in the 2010s and early 2020s that highlighted rising risk for many regions. As climate change progresses, the frequency and intensity of Hitzewellen are expected to increase in many areas.