UK raises heatwave temperature threshold, IMD predicts heatwave spell

The United Kingdom has raised the temperature at which forecasters will declare a heatwave in an area as climate change makes these extreme weather events more frequent. Heatwaves are defined as happening when a location records at least three days in a row with daily maximum temperatures meeting or exceeding a certain threshold. The heatwave definitions are designed to be relative to the current climate, and with average temperatures rising in the UK as a result of global warming, the thresholds are being increased for parts of England. UK Meteorological office raised the thresholds in some counties from 27 degrees Celsius to 28 degrees Celsius threshold and in others from 26 degrees Celsius to 27 degrees Celsius followed by 25 degrees Celsius to 26 degrees Celsius in one.

Previous heatwave thresholds were based on the climate in the period 1981-2010, and were intended to be reviewed and revised to represent heatwaves relative to the current climate, the Met Office said. The new thresholds are based on the climate from 1991-2020, which was brought in as the reference period in January this year, and are being updated ahead of summer. The decision comes in the backdrop of global warming intensifying the occurrence of these weather-related events. 

India also facing the impact of climate change. The India Meteorological Department on Tuesday predicted a heatwave spell over Northwest, Central & West India for the coming four to five days. The IMD in a statement said that there could be a gradual rise in maximum temperatures by about 2 degrees Celsius over many parts of Central and East India during the next three days. The weather agency warned that heatwave could lead to moderate health concerns for vulnerable people and there is an increased likelihood of heat illness symptoms in people who are either exposed to the sun for a prolonged period or doing heavy work. The India Meteorological Department defines a heatwave as a condition of air temperature which becomes fatal to the human body when exposed. "It is defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal. In certain countries, it is defined in terms of the heat index based on temperature and humidity or based on the extreme percentile of the temperatures."

IMD considers an area experiencing a heatwave if the maximum temperature of a station reaches at least 40 degrees Celsius or more for the plains and at least 30 degrees Celcius or more for hilly regions. A heatwave is also characterised if the temperature goes at least 4.5 to 6.4 notches up and if ts exceeds over 6.4 degrees Celcius above normal, the IMD classifies it as a severe heatwave. In the Coastal region, a heatwave is announced if the maximum temperature is 4.5 degrees Celsius or more than the normal temperature experienced in the area. The heatwave threshold in India is high compared to what the United Kingdom has deemed fit to declare a heatwave, since India has tropical weather conditions where temperatures are generally high.