Published in ‘Down to Earth’, a fortnightly brought out by the Centre for Science and Environment, the report points out that meteorological data shows that March and April have been warming faster in the last 100 years. The average temperature for March has increased by 0.76 degree Centigrade over the last century and for April by 0.58 degree Centigrade.

Quoting a study by the India Meteorological Department (IMD), the report says that on average, almost 23 sub-divisions were hit by heatwaves between 1991 and 2000, while 10 sub-divisions were affected in 1981-1990 and only seven were hit in 1971-1980. The survey compared the number, duration and spread of heatwaves from 1971 to 2000 in 35 sub-divisions across the country.

In 1991-2000, 25 sub-divisions went through more than 15 spells of heatwaves, compared to only two in the previous two decades. Notably, 1991-2000 was the warmest decade in the past 140 years.

In March-April this year, over 70 people died in Orissa reportedly due to sunstroke, with the mercury soaring to 46 degree Centigrade in April in some big cities.

In West Bengal, the heat wave killed nine. “Abnormal” dry spells and dust storms swamped Guwahati, while the entire Malwa region in Madhya Pradesh reeled under severe water stress, says the report.

According to the IMD, disturbances in the air circulation pattern over India led to the mercury soaring across the country. Circulation of air helps to distribute heat over the earth.

The cyclonic storm, Bijli, which formed in the Bay of Bengal in mid-April, cut off the cool easterly winds blowing in from the Bay of Bengal. To add to it, an anticyclone hovering around Rajasthan blew hot winds from northwest to central and western India.

Some scientists have attributed the heatwave to an exceedingly dry winter, while others have pointed to the unusual heating of the Tibetan Plateau, which was two degrees warmer than normal in February this winter, says the report.