Pre-monsoon showers usually cool down summer days and nights but Kerala is witnessing heatwaves without these rains.
Unabated heat wave in Kerala.
Kerala and much of south India are witnessing unusually high summer temperatures, with heatwave conditions in several districts. The IMD notes that this weather condition will likely continue until 6 May.
The spell of warm weather—felt over Kerala, Mahe, coastal Karnataka, Tamil Nadu, Puducherry, Karaikal, and Konkan, as the IMD notes—is an outcome of atmospheric and ocean phenomena. Scientists point out that this has human-made and natural causes.
IMD’s Meteorological Centre of Thiruvananthapuram noted on their website on 3 May: “Maximum temperatures are very likely to be around 40˚C in Palakkad district, around 39˚C in Kollam, Thrissur & Kozhikode districts around 38˚C in Alappuzha, Kottayam, Pathanamthitta & Kannur districts, around 37˚C in Thiruvananthapuram, Ernakulam, Malappuram & Kasaragod districts (3 to 5˚C above normal) during 2nd May 2024 to 06th May 2024. Heat Wave conditions likely to prevail at one or two places in Alappuzha, Palakkad, Thrissur & Kozhikode districts on 2nd & 3rd May 2024.”
So far, it is a yellow warning, advising “be aware”.
Scientists point out that the warming trend is an indication of climate change. Human activities such as fossil fuel burning alter the composition of the global atmosphere and add to natural climate variability. Climate variability means variations in the mean and other climate statistics beyond individual weather events. It may be due to natural processes within the climate system or variations due to natural (e.g., volcanic eruptions) or human-made external influences (e.g., air pollution).
“2023 was the hottest year of the century. We’re seeing it as a continuation,” Prof S Abhilash, director of the Cochin University of Science and Technology (CUSAT) Advanced Centre for Atmospheric Radar Research, told South First. “El Niño has impacted atmospheric circulation. That has led to high-pressure areas over south India and the Arabian Sea. That means more warming of the atmosphere and less cloud formation. In turn, northern Kerala has less rain and high temperatures.”
Abhilash’s statement packs in a lot of science. First, global temperatures are rising. The systematic recording of temperature data started in 1850. Since then, 2023 has been the warmest year. The year notched up an average global temperature of 14.98°C, 1.48 degrees Celsius warmer than the 1850-1900 average. That is close to the 1.5-degree Celsius mark associated with moderate climate change projections.
What we witnessed in 2023 was not an on-off phenomenon. On the contrary, it was part of a clear warming trend. “Since the 1980s, each decade has been warmer than the previous one. The past nine years have been the warmest on record,” the World Meteorological Organization (WMO) has stated. The UK Met Office has noted that scientists are concerned that 2024 average temperatures could overtake 2023.
Scientists have recognised climate change as the primary reason for the warming trend. Average air temperatures have been rising just above the earth’s surface. This is due to what they call the greenhouse effect. That means heat is trapped near the Earth’s surface by greenhouse gases like a blanket wrapped around the planet. WMO notes that the three main greenhouse gases in the atmosphere—carbon dioxide, methane, and nitrous oxide—have reached record highs and are likely to rise further.
Burning fossil fuels such as coal, gas, and oil, as well as construction and industrial processes, emit excess carbon dioxide. Farming, dairy keeping, and waste management emit methane and nitrous oxide.
Climate change impacts add to natural climate variability. A key current factor is El Niño. Simply put, El Niño denotes the unusual warming of surface waters in the eastern equatorial Pacific Ocean. El Niño also impacts trade winds and the atmosphere.
El Niño modifies the atmospheric flow and affects local weather for half a year to one year in many parts of the world, including India. It is coupled with the Southern Oscillation phenomenon, which denotes changes in sea-level air pressure patterns in the Southern Pacific Ocean between Tahiti Island and Darwin, Australia.
El Niño affects a contributory factor of the monsoon called the Walker Circulation. It is an east-to-west circulation across the tropics at low levels and a west-to-east circulation at upper levels of the atmosphere. The upward branch circulation over a large area around Indonesia shifts east during El Nino years following the anomalous ocean warming.
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Meanwhile, the downward motion that involves anomalously high surface pressure occurs around Indonesia. If ocean warming is mostly in the central Pacific, sinking branches of the circulation expand to cover India, reducing the monsoon.
Pre-monsoon showers usually cool down summer days and nights. However, with heatwaves without these rains, Kerala’s day and night temperatures remain high. IMD senior scientist and monsoon expert Dr Sivananda Pai has told the media that the prevailing dry weather has contributed to the rise in temperature.
IMD declares heat waves based on a set of criteria. As IMD notes: “Qualitatively, a heat wave is a condition of air temperature which becomes fatal to the human body when exposed.
Quantitatively, it is defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal.” Further, when the maximum temperature of a station reaches 40 degrees Celsius or more for plains and 30 degrees Celsius or more for hilly regions, it can be considered a heatwave. For coastal stations, when the maximum temperature departure is 4.5 degrees Celsius or more from normal, and the actual maximum temperature is 37 degrees Celsius or more, IMD describes it as a heatwave. Going by these criteria many parts of south India are experiencing a heatwave.
IMD notes that the movement or prevalence of hot, dry air over a region aids heat waves. So does the absence of moisture in the upper atmosphere. A cloudless sky and large-amplitude anti-cyclonic flow over the area also help heat waves.
As observers note, south India needs a spell of cooling rains.
(The author is a geographer who is researching marine weather, climate change, and people’s responses. He has reported science for leading publications and won the Prem Bhatia Award for environmental journalism. He lives in Bengaluru. Views are personal.)
(Edited by VVP Sharma)
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