A day after Rajasthan's Phalodi recorded the country's highest temperature ever of 51°C, the India Meteorological Department said the frequency of severe heat waves had increased sharply in the past 15 years. Most heat-affected states have no plan in place to prevent mortality and morbidity associated with extreme heat. IMD officials said the average frequency of severe heat waves had doubled from 50 days a year across India until 2000, to about 100 in the 2001-2010 decade. The figures are cumulative numbers from all IMD stations. So, if there are 10 severe heat wave days in two cities simultaneously, it's counted as 20.

Most heat-affected states have no plan in place to prevent mortality and morbidity associated with extreme heat. IMD officials said the average frequency of severe heat waves had doubled from 50 days a year across India until 2000, to about 100 in the 2001-2010 decade. The figures are cumulative numbers from all IMD stations. So, if there are 10 severe heat wave days in two cities simultaneously, it's counted as 20.

"The frequency of both heat waves and severe heat waves has increased, particularly in the last two decades. The reasons could be related to climate change, urban heat island effect or others," said B P Yadav, director, National Weather Forecasting Centre at IMD.

He added that between 2010 and 2016 too, heat waves showed an upward trend. IMD has started issuing a separate colour-coded heat wave forecasting from this year, which alerts agencies on when interventions are required, because of what it called a "visible increase" in both mean temperature and heat wave incidents.

IMD's observations correlate with warnings by the Intergovernmental Panel on Climate Change (IPCC) of a steady increase in warm days and nights globally, and higher temperatures in cities due to the urban heat island effect.