According to the India Meteorological Department, Delhi has received 128.2 mm of rain so far this month, the most for October in a whopping 66 years. The city received 236.2 mm of rain in October 1956, according to the IMD. The all-time monthly rainfall record in Delhi is 238.2 mm, set in 1954. The 128.2 mm of rain received until 8.30 a.m. on Tuesday is also the city’s fourth highest October rainfall total.
Meanwhile, other states have also been witnessing heavy rainfall including Uttar Pradesh. The state has seen 11 deaths due to rain-related incidents recently. But why are rains still going strong even as the middle of October approaches? News18 explains:
Western Disturbances Cause Formation of Trough
Rains have been reported in several parts of northern India as a result of a western disturbance that has formed as a trough in the mid and upper tropospheres. The trough runs along 64 degrees East to the north of 25 degrees North, with a cyclonic circulation in lower tropospheric levels over south Haryana and its surroundings, according to a report by India Today.
The troposphere is the lowest layer of the atmosphere, stretching 10 kilometres above sea level and containing the majority of clouds, including rain-bearing nimbus clouds. The interaction of the western disturbance and the cyclonic circulation is causing heavy rains in parts of Bihar, Uttar Pradesh, and Uttarakhand.
On October 11, the trough is expected to bring widespread heavy rain and thunderstorms to Uttarakhand, Punjab, and West Uttar Pradesh during the day, as well as parts of eastern Uttar Pradesh. Previously, easterly winds carried moisture from the Arabian Sea as a result of another trough extending from Delhi to east Rajasthan, causing heavy rains in the previous week.
The Spill Into October…Not Surprising?
According to a report by Indian Express, the India Meteorological Department (IMD) revised the expected dates of monsoon onset and withdrawal for several regions of the country three years ago. To account for trends observed over the last 50 years, the withdrawal dates for North, Northwest, and Central India were pushed back by one to two weeks.
M Rajeevan, former Secretary, Ministry of Earth Sciences told the publication, “People will have to get used to it. These are not freak events. We are likely to see these happening in the coming years as well.”
Should IMD Change Definitions Amid These Patterns?
A report by Down to Earth states that IMD will not classify the current rainfall as monsoon rainfall because the weather agency stops recording monsoon data on September 30.
Any rainfall after this date is considered ‘post-monsoon rainfall,’ despite the fact that the rainfall is primarily caused by weather systems that form during the monsoon season. This is the third year in a row that this has occurred.
A similar stretch of rain into October occurred in 2021 and the year before that. This necessitates an examination of India’s current definition of the monsoon season, which runs from June to September, and the inclusion of the current October rains within that definition, the report argues.
Raghu Murtugudde, a climate scientist at the University of Maryland and the Indian Institute of Technology, Bombay, told Down To Earth that “if the trend continues, the definition of the monsoon may have to change."
“It’s not a good idea to simply go by a calendar date anyway," he added, “but that’s historical baggage that has to be dropped now."