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October 2024 was the hottest October month for India since 1901 in terms of mean temperatures and minimum temperatures, according to the India Meteorological Department (IMD) and at least a part of the reason could be global warming.
For Delhi specifically, where not even a drop of rain fell in the month, October has been the warmest since 1951, according to IMD.
While the reason for such high temperatures across some regions such as the northwest could be lack of western disturbances and rainfall, the overall reason could be a background warming which has cranked up temperatures in various countries across the world over the past couple of years and particularly in October.
The decrease in western disturbances in winter months has also been attributed to warming atmosphere and oceans and subsequent changes in global atmospheric patterns.
The mean temperature records for various regions within the county have also fallen. October 2024 was the warmest since 1901 for central India while it was the second warmest for northwest India and third warmest for south peninsular India.
In terms of minimum temperatures all regions of the country along with the country as a whole broke their records since 1901.
The month of October is the transition between the rainy season and the winter season for large parts of the country, but it is also sometimes known for higher-than-normal temperatures because of the retreating monsoon.
The reasons for this are higher humidity levels in the atmosphere because of residual moisture left behind by the retreating monsoon winds. The water vapour, being a greenhouse gas (GHG), traps the heat.
If there is no local or major convection or winds that bring rainfall, then the heat does not get dissipated and keeps building up in the atmosphere leading to warm sultry conditions which is what seems to have happened across India in October 2024.
At least in northwest India, the regular disruption to the building up of heat comes from western disturbances which are extra tropical storms that originate in the Mediterranean region and bring most of northwest India’s winter rainfall and snowfall for the mountains.
There have been no recorded western disturbances that have affected northwest India in October 2024, according to data from the IMD.
Northwest India received 76 per cent less rains than normal between October 1 and October 30, according to data from the IMD.
India is not the only country in the world suffering from such high temperatures. Japan has also recorded its warmest October month since 1898, according to data from the Japan Meteorological Agency.
In fact, record heat from west Asia to Japan including India and Pakistan will continue into November, according to climatologist and weather historian M Herrera on X.
For every one-degree Celsius rise in global average temperatures, there is a 7 per cent increase in moisture levels which adds to the GHGs in the atmosphere and increases the heat indices or felt temperatures or wet bulb temperatures (different measures informing about the combined heat impact of heat and moisture in the atmosphere).
The combination of high temperatures and high humidity levels that can cause humid heat waves or heat wave like conditions are already becoming common but may become even more frequent as the world warms further due to GHGs lodged in the atmosphere and that will be added in the near to far future.