One of the clichéd references to Chennai’s seasons — hot, hotter and hottest — was never a joke, and less so these days. Harsh summer days started earlier this year as the mercury crept up steadily, several notches above the average daily temperature for the season by late March. Just two days into April, Chennai experienced its first hottest day of the year as the maximum temperature peaked to 41.2 degrees Celsius, nearly 7.4 degrees Celsius above average. This is rather unusual.
In recent decades, summers in Chennai are becoming hotter. Though not alarming, meteorologists and experts note that there is, indeed, an increasing trend in the rising mercury level. Record-breaking temperatures and blistering heat became a common thread across many parts of Tamil Nadu and the coastal city this year as an intense heat wave tightened its grip on at least 20 districts for nearly five days till April 4. The sun was brutal in interior districts that sizzled till April 7.
Heat wave, a period of excessive hot weather with the day temperature crossing 4.5 degrees Celsius above normal, is usually associated with peak summer days after mid-April. But this year, the heat wave spell set in a bit early, prolonged for more than five days and the temperatures soared seven degrees Celsius above normal in some places, especially in Chennai.
The India Meteorological Department (IMD) had released a seasonal outlook for temperatures between March and May this year. It had predicted a below normal temperature in the southern peninsular region this summer. However, officials noted that there was only 60% probability in the forecast for Tamil Nadu, given its varied climatological conditions in different locations.
S. Balachandran, Deputy Director-General of Meteorology, Chennai, says that in the city, there had been a slight increase by 0.02 degree Celsius in May’s daily maximum temperature, going by the data for 1990-2003. At Meenambakkam, the increase in the daily maximum temperature is 0.006 degree Celsius, which is marginal. “There is a slight spike in the temperature over the recent decades. But there is no drastic change.”
What caused early heat wave
Dry land winds and the weather system over the Bay of Bengal that disturbed the wind flow pattern and prevented cool easterlies into the Tamil Nadu region were the reason for the severe heat wave. But it is a temporary phenomenon and may not occur every year, Mr. Balachandran says. The IMD now issues a two-week extended range forecast and a detailed health advisory, along with heat wave warnings, as part of the impact-based forecasts. “We are also strengthening observation networks for location-specific data and better forecasts in the city,” Mr. Balachandran adds.
Contributing factors
Meteorologists note there are several factors — wind direction, clouding or sea breeze — that influence scorching weather. Summer heat is felt more now as the length of the day increases after equinox day in March and according to the declination of the sun. In Chennai, easterly winds from the sea blow till the third week of April and hot westerlies set in.
Weather expert Y.E.A. Raj says sea breeze is a significant factor that often saves Chennai from brutal heat. Those closer to coastal areas and even those within the city may have a quicker respite. For instance, the day temperature may soar to the same level of 40 degrees Celsius in both Vellore and Chennai. But it may drop rapidly in Chennai with the sea breeze blowing in. But Vellore has to wait for radiation cooling as cool easterlies may not penetrate that far.
“We cannot compare the surface heat of Chennai with that of interior places. Coastal places like Chennai have the advantage of sea breeze. While mercury level drops in other places after May because of the south-west monsoon, it is for the same reason that Chennai remains hot even during June. Strong westerlies often lead to peaking mercury level and discomfort in June,” Mr. Raj says.
In 2019, one of the hottest years of the decade, Cyclonic Storm Fani and Cyclone Vayu impacted the sudden spike in temperature, and June had too many hot days. “The number of hot days in which the temperature breached the 40-degrees Celsius mark has gone up in the city recently. The impact of global weather changes and urban heating following rapid urbanisation cannot be denied,” he adds. Studies, too, indicate an upward trend in the day and night temperatures, especially during summer, over the past three-four decades. Citing a study ‘Trends of the observed temperature and its variations in Tamil Nadu’ he authored with Anushiya Jeganathan and A. Ramachandran, K. Palanivelu, Director, Centre for Climate Change and Disaster Management, Anna University, says the mean maximum temperature has shown an increase from 0.01 degree Celsius to 0.54 degree Celsius at various places over the past four decades. Though not alarming, there is a steady rise in Chennai’s temperature levels, too, especially during summer.
“The daily average temperature may go up by 2 degrees Celsius-3 degrees Celsius by 2100. We need to minimise carbon emissions and switch over to renewable energy. Green cover must be increased to control the spike in temperature. People may feel cooler in areas with green cover or waterbodies. For instance, IIT-Madras may have cooler temperature than, say, Saidapet. Carbon-dioxide captured from power plants could be converted into value-added products,” he says.
Impact on health
Humidity compounded the problem for residents in the coastal region around April 5 and 6 when the levels were more than 77%. With the moist easterlies returning, higher humidity levels made it feel hotter than actual temperature.
The soaring heat level has its own effects on one’s health. At a time when coronavirus infections are spreading rapidly, the rising temperature and its health impact should not be forgotten, say doctors.
V. Rajendran, associate professor of medicine, Rajiv Gandhi Government General Hospital, said that on average, the hospital handles 30 to 50 patients with heat-related symptoms every year between April 15 and June 15. “Heat exhaustion is more common than heat stroke. But heat stroke is more dangerous. It is important to take precautions. Very young children and persons aged above 65 should avoid going out, especially during the hottest part of the day,” he said. Dehydration, drowsiness and tiredness are the most common symptoms of the heat’s effect on the body. The symptoms of heat exhaustion include general weakness, elevated body temperature of above 103 fahrenheit, rapid and strong pulse or heart rate, loss or change of consciousness, hot, red, dry or moist skin, he says.
Beating the heat: Coolers such as lemon juice and carbonated water or soda are go-to drinks for the man on the street to beat the heat during summer.
“We are seeing an increase in the number of cases of COVID 19. While we are concerned about a second wave of the pandemic, heat wave and heat-related illnesses should not be forgotten. Hospitals in Vellore see many patients who present themselves with heat related-illnesses in summer. This is usually associated with heat waves — periods of abnormally hot and usually humid weather,” explains Anand Zachariah, professor and head, Medicine-I, Christian Medical College, Vellore.
What causes heat strokes
When the body is unable to release heat through sweating, the temperature rises. The brain cannot tolerate the increase in body temperature, and this leads to unconsciousness or drowsiness. Heat stroke is a condition which occurs in summer with elevated body temperature (over 40 degrees Celsius) and altered consciousness. The elevated body temperature can also cause damage to other vital organs, Dr. Zachariah says. Older people, patients with heart, lung, kidney, neurological, psychiatric, skin conditions and obesity are at an increased risk of developing heat stroke. He says that making available safe drinking water in public places is important.
The elderly and children need additional care during summer. As senior geriatrician V.S. Natarajan says elderly persons, unlike any other age group, would not be able to withstand heat levels and are highly sensitive. “The thermoregulatory centre in the brain does not function normally in the elderly. They will have excessive sweating that could lead to hypotension, and they could also lose sodium, resulting in hyponatremia. They could experience extreme tiredness, nausea, vomiting, headache, dryness of tongue, reduced urine output, lack of proper sleep and reduced food intake,” he explains.
With thirst sensation reduced in the elderly, he says senior citizens, except those with cardiac and renal diseases, should drink a minimum of two to three litres of water a day.
S. Balasubramanian, medical director, Kanchi Kamakoti CHILDS Trust Hospital, says that when children play without drinking adequate water, they may get dehydrated. Inadequate water may also cause urinary tract infections. “Children get prickly heat during summer. This could get infected if they scratch the rash. Summer is also the time when food-borne and water-borne diseases occur as eating out is common. There is a high risk of typhoid, diarrhoea and food poisoning,” he points out.
