A heatwave is an extended period of hot weather relative to the expected conditions of the area at that time of year.
What is a heatwave?
A heatwave refers to a prolonged period of hot weather, which may be accompanied by high humidity. The World Meteorological Organization guidance around the definition of a heatwave is “A marked unusual hot weather (Max, Min and daily average) over a region persisting at least two consecutive days during the hot period of the year based on local climatological conditions, with thermal conditions recorded above given thresholds.” They are common in the northern and southern hemisphere during summer, but classification and impacts vary globally.
Why do heatwaves happen?
Heatwaves are most common in summer when high pressure develops across an area. High pressure systems are slow moving and can persist over an area for a prolonged period of time such as days or weeks. They can occur in the UK due to the location of the jet stream, which is usually to the north of the UK in the summer. This can allow high pressure to develop over the UK resulting in persistent dry and settled weather.
The UK experiences occasional heatwaves but of a lesser frequency and intensity of those seen elsewhere globally. In August 2003, the UK experienced heatwave conditions lasting 10 days and resulting in 2,000 deaths. During this heatwave, a record maximum temperature of 38.5 °C was recorded at Faversham in Kent. In July 2006, similar conditions occurred breaking records and resulting in the warmest month on record in the UK.
To aid in the preparation and awareness before and during a spell of very hot weather, a heatwave plan has been created by Public Health England in association with the Met Office and other partners. It recommends a series of steps to reduce the risks to health from prolonged exposure to severe heat for:
- The NHS, local authorities, social care, and other public agencies
- Professionals working with people at risk
- Individuals, local communities and voluntary groups