Heatwave

A heatwave is a period of unusually hot weather that lasts for several days, typically two or more consecutive days, and is substantially hotter than the local climate norms for the season. The exact thresholds vary by country and region, and some agencies define a heatwave as a stretch with daily high temperatures above a historical percentile or above a local record.

Heatwaves are most often driven by persistent high-pressure systems that trap heat and suppress cloud formation, allowing temperatures to rise and nighttime relief to be limited. Dry conditions can amplify heat, while humidity can affect the perceived heat. Climate change is increasing the frequency, intensity, and duration of heatwaves in many areas by warming baseline temperatures and altering atmospheric circulation patterns.

Definitions differ; thresholds may be based on long-term climate normals, percentile-based criteria, or records. Regions may also consider night-time temperatures and heat indices when evaluating public risk.

Heatwaves pose health risks, including heat exhaustion and heat stroke, with the elderly, children, outdoor workers, and people with chronic illnesses at highest risk. Other impacts include dehydration, disrupted sleep, and increased demand on electricity and cooling infrastructure. Physical systems such as roads, railways, and power grids can suffer from heat damage and outages. Agriculture and ecosystems may experience stress, drought, and wildfires.

Mitigation and adaptation include public warnings, cooling centers, hydration guidance, and restrictions on outdoor work schedules to reduce risk. Urban design with shade trees, reflective surfaces, and better building ventilation reduces indoor heat. Long-term adaptation also involves climate-sensitive infrastructure and emergency planning.