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A spring to summer

The scorching heat will continue for at least a week, but it may be too soon to blame climate change, reports Anika Gupta.

delhi Updated: Apr 16, 2010 01:56 IST
Anika Gupta

At least another five days of scorching weather lies ahead for Delhi as the record-breaking heat wave that has burned most of India and left several people dead since mid-March continues.http://www.hindustantimes.com/images/HTEditImages/Images/hot-april-15.jpg

“We expect hot conditions over northern and central India to continue for five to seven days,” said H.R. Hatwar, who oversees research for the India Meteorological Department (IMD).

According to IMD data, Delhi’s April temperatures normally hover between 20 and 37 degrees in April.

The April temperatures are still closer to the average than March temperatures.

This March was the hottest for many places in the country, especially the far northern states and the east.

In Delhi, the March temperature has been on average between 14 (minimum) and 30 (maximum) degrees for the past half a century. This year, temperatures climbed as high as 39.2 degrees.

In the Himalayan region, temperatures have been 10 degree Celsius above normal.

Numerous factors combined to create the current weather crisis, but the most significant had been the absence of western disturbances, or blasts of cold air and storms that normally come into India from over Russia, said Hatwar.

Western disturbances move across India, bringing with them cool, moist air from the north. This year’s western disturbances have been weak and far between.

In the absence of cold storms, the hot dry air that blows into India from the western desert collects close to the earth, a trend known as atmospheric subsidence. As there are fewer clouds, the earth receives more of the sun’s baking rays. All these factors combine to create strong heat.

This heat has affected the media as well, and many sources have rushed to attribute the higher temperatures to global warming.

On Monday, the Centre for Science and Environment, a non-profit organisation, released a statement saying there was enough scientific evidence to link the current heat wave to global warming. Not only were this year’s temperatures unusually high, 2009 was also unusually warm.

But other scientists are cautious.

“Heat waves are quite common and there’s nothing abnormal about having one,” said Ravi S. Nanjundiah, professor at the Centre for Atmospheric and Ocean Sciences at the Indian Institute of Science, Bangalore. “What’s unusual is that the heat wave started in April rather than later in the year, like May.”

Although recent research by scientists at the Indian Institute of Tropical Meteorology (IITM), Pune, and elsewhere has suggested that average temperature all over India has risen by 0.2-0.6 degree Celsius, it is difficult to say whether individual heat waves are the result of climate change or just the product of regional weather variations. Since 1901 there have been five years when the temperature in March touched 39 degrees.

“We can’t say yet whether this particular heat wave is related to climate change,” said R. Krishnan, programme manager for the Centre for Climate Change Research at the IITM. “(But) climate change has definitely increased global temperatures.”

“It’s hard to attribute any heat wave that happens once or twice in a season to global warming,” said K. Krishna Kumar, an IITM scientist who authored a recent paper on mean temperature increases. “Obviously as temperatures rise, the likelihood of heat waves increases.”

Nanjundiah suggested that the creation of urban “heat islands” might also be contributing to the unusually high temperatures in cities. Building materials like concrete soak heat and block air flows, resulting in higher temperatures. As urban density and construction increase across India, temperatures in cities could also rise.

Increased construction was one of the causes suggested for the recent heat wave in Kerala, where the temperature reached 45 degrees in some parts of the state (almost 5-6 degrees above normal), resulting in several deaths.

There is hope, however. Warmer temperatures, especially in the north, sometimes favour an early monsoon, says Krishnan. This chimes with a previous IMD report that this year’s monsoon will be normal, after last year’s drought.

“High temperatures over the subcontinent and over the Eurasian region are generally favourable for a good monsoon,” Krishnan said.

When asked whether this year’s abnormally high temperatures could become the norm as global temperatures rise, he chuckled.

“That is a very complex question,” he said. “Unfortunately, it is difficult to predict exactly what will happen.”