Heatwave

Heatwave

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. Although in the UK there is no official definition of a heatwave the World Meteorological Organization definition is "when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C, the normal period being 1961-1990". Heatwaves are common in the northern and southern hemisphere during summer and 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. A heatwave 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.

Classification

Working in association with the Department of Health, the Met Office provides a Heat-health watch system for England.

The Heat-health watch system comprises four levels of response based upon threshold maximum daytime and minimum night-time temperatures. These thresholds vary by region, but an average threshold temperature is 30 °C by day and 15 °C overnight for at least two consecutive days.

Threshold temperatures
RegionDay max (°C)Night min (°C)
North East England2815
North West England    3015
Yorkshire and the Humber2915
West Midlands3015
East Midlands3015
East of England3015
Southeast England3116
London3218
Southwest England3015
Wales3015

Impacts

The UK experiences occasional heatwaves but of a lesser frequency and intensity of those seen elsewhere globally. In August 2003, a recording breaking resulted in the UK experiencing 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 heatwave 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 heatwave, 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

Last updated: 2 August 2013