Many a times human perceptions create illusions. Illusions based on our observations around us. Illusions based on personal memories. Memories that get influenced by recent past events. Rains are also no exception to this. Often we have people complaining about poor rains in their places. This becomes a contentious point when one points out about good rains overall. The best way forward to this is to look at data. Data that can point out the truth without human bias. So how good has been Tamil Nadu rainfall this year? This post will try to answer that question.
Before we get to the nuts and bolts of the post it is essential to point out a good year all around may not compensate for a bad year in a specific place. But certainly a good year at most places mean better water availability on a larger scale. Rainfall calendar and seasons are a human creation. IMD created four seasons for administrative convenience and long term data keeping. As far as Tamil Nadu is concerned it goes without saying Northeast Monsoon is the key season. Only 8 districts in the state receive less than 40% of their annual rainfall during Northeast Monsoon season. 6 districts, Karaikal from Pondicherry UT, receive more than 2/3rd of their annual rainfall during Northeast Monsoon.
The post does not aim to undermine the importance of Northeast Monsoon to Tamil Nadu rainfall. With this caveat now let us try to see how 2024 has been so far. Out of the 40 districts, including two from Pondicherry UT, 15 districts have already reached 90% of their annual quota. This list is filled up by interior districts with the exception of Tiruvallur. Tiruvallur interestingly benefitted from a very strong Southwest Monsoon season like the neighbouring Chennai. Among these 15 districts, Tirunelveli, Coimbatore, Nilgiris and Theni has crossed their annual average.
Excluding the above four districts 14 out of the rest 36 districts require less than 40% of normal rains during the remaining Northeast Monsoon season. On the other side of the scale 14 districts require a minimum of 75% of rainfall during the remaining days to reach annual average. Mayiladuthurai, Perambalur, Nagappattinam, Kallakurichi and Thoothukudi need above average rains to reach annual average. Effectively these 5 are the vulnerable districts for ending the year in negative if remaining days do not fetch good rains.
As far as KTCC districts go as mentioned above Tiruvallur is very close to reaching its annual average. Chennai, Chengalpattu and Kanchipuram overall require only 25 cms to reach their annual average rainfall. The very good Southwest Monsoon season no doubts helped these districts reach such a situation. In this context one wonders why people always think the rains have been poor so far and we are heading towards a tough summer in 2025. The less than 50% storage levels of the drinking water lakes around Chennai may be contributing to this thinking. With two months of Northeast Monsoon still left there is no reason to panic.
On the weather front gradually from today with Easterlies strengthening coastal areas of Tamil Nadu may see increased rainfall activity. The stretch south of Delta districts may see a more pronounced rainfall activity. Like the past couple of days South and West TN may see widespread rains with few places in Kanyakumari district seeing very heavy rains. Chennai and suburbs may see isolated light / moderate rains during morning hours.