On Tuesday afternoon, the coastal air of Chennai was dryer than usual. Gusts of warm wind blew through the treeless streets of the city. A heat wave had set in over the city, and this time, there are fewer trees to take it on.

Residents have been advised by the district authorities not to step out of their homes between noon and 3 pm. On April 17, the India Meteorological Department had issued a heat wave warning for 18 districts in Tamil Nadu, as temperature in several places crossed the 40 degrees Celsius mark. On Monday, the Chennai airport recorded a temperature of 42.2 degrees Celsius, which is 6.5 degrees above normal. The Tamil Nadu State Disaster Management Agency alerted the collectors of affected districts to take precautions in the event of high temperatures.

“It will take at least a couple of days for the heat wave to recede,” said a duty assistant at the Regional Meteorological Centre in Chennai. “But the temperature will reduce only by one or two degrees. This April is going to remain quite warm.”

There is little that can be done other than to stay indoors and wait for the heat wave to pass. With one-fourth of the city’s tree cover destroyed by the cyclonic storm Vardah on December 12 and several lakes running dry, the natural defences of the city to take on summer heat are at an all time low.

No respite from sea

The heat wave was brought on by Cyclone Maarutha, formed over the Bay of Bengal. A few days ago, it began moving away from peninsular India and made a landfall on the west coast of Myanmar on Monday. Weather experts said the cyclone absorbed a great amount of moisture from the Tamil Nadu coast, leaving clearer skies and weak sea breeze.

For a coastal city, the breeze from sea to land, which begins to blow at around noon, tends to keep the atmosphere from extreme heating. But the cyclone has caused sea breeze to be replaced with land breeze, bringing warm, dry winds from interior regions to the coast.

“These winds from the west normally do not reach the coast since they are usually opposed by winds from the sea,” said Pradeep John, an independent weather blogger. “But a similar heat wave set over Chennai in May 2003 when a cyclone moved away from the coast, leading to persistent land breeze. The temperature then shot up to an all-time high of 45 degrees in the city.”

The intense dryness increases the chances of thatched huts and faulty electric points catching fire from the smallest spark. Although the fire department has not recorded a significant increase in the number of fire cases, fire officer Balasubramniam of Ashok Nagar said they were receiving a lot of calls about garbage dumps and waste being set of fire by residents. “These things catch fire immediately since there is barely any moisture in the air,” he said. “Vardah destroyed most of our trees, and that has also contributed to the problem.”

Furnace of a city

The December cyclone uprooted over one lakh trees across Chennai, leaving little canopy cover over the city.

“The reduction in trees due to Cyclone Vardah is one of the reasons for the increased radiation [of heat] in the city,” said Srikanth, the co-founder of Chennai Rains portal, a weather blogging site. “It has not caused a rise in temperature but has aggravated what was started by land breeze and the lack of moisture.”

John said that if a city had a larger paved surface, it would reflect more heat. For example, while walking barefoot on cement one feels the heat far more than while walking on grass. Similarly, tree canopies absorb heat, so it feels cooler in a wooded area. But the actual temperature in the city may be the same.

“Just because trees have been lost, it does not mean it is going to become hotter,” John said. “But the urban heat island effect is going to be higher.”

Chennai has always been infamous for its sweltering summers. But without a quarter of its tree cover, it’s going to be much harder to bear this summer.