Waterlogged roads, flooded subways, boats out to rescue elderly citizens—for the people of Chennai, December 4 evoked memories of the 2015 deluge. Like in 2015, this time too the rainfall has been described by authorities as ‘unprecedented’. Just how much rainfall did Chennai receive this time and is it comparable to 2015?
According to the India Meteorological Department (IMD), Poonamallee recorded the highest rainfall between December 4-5 at 34 cm. Avadi in Tiruvallur district recorded 28 cm of rainfall, Tambaram in Chengalpattu received 24 cm, and Chembarambakkam in Kancheepuram saw 21 cm of rainfall. Chennai’s Nungambakkam, meanwhile, recorded 24 cm of rainfall, while Meenambakkam received 19 cm between December 4 and 5.
On December 1, 2015, Tambaram recorded over 49 cm of rainfall, while Chembarambakkam recorded over 47 cm in 24 hours. Nungambakkam received more than 29 cm, while Meenambakkam recorded nearly 35 cm.
So if we compare rainfall statistics purely from a 24-hour window, the rainfall received in 2015 was higher than this year. But weather bloggers like K Srikanth of Chennai Rains point out that in the case of the 2023 floods, it’s important to look at a 48-hour window. This is because IMD records rainfall data from 8.30 am to 8.30 am the next day. In the recent floods, the highest amount of rainfall was recorded between 8.30 pm on December 3 and 8.30 pm on December 4. “That’s why the amount of rainfall recorded is split across two days in IMD’s statistical books,” explains Srikanth.
Looking at IMD’s 48-hour window reveals the sheer intensity of rains that pounded the city and its suburbs and shows that the rainfall surpassed 2015. Between December 3 and December 5, Chennai’s Nungambakkam recorded 47 cm of rainfall, while Meenambakkam received 42 cm of rainfall. Tambaram in Chengalpet recorded 41 cm of rainfall, while Chembarambakkam recorded 37 cm of rainfall. Avadi recorded a whopping 56 cm of rainfall between December 3 and 5.
So why was the scale of destruction more in 2015 compared to 2023? At least 250 people were killed in the December 2015 floods. As of December 5, 2023, 12 people have been killed in rain-related incidents in Chennai.
The floods in 2015 were exacerbated by the mismanagement of the Chembarambakkam reservoir on December 1, when water was suddenly released. The huge release of water caused the Adyar river to flood. Srikanth says this is the lesson the Tamil Nadu administration and successive governments have learnt since 2015. “This time, water has been released from Chembarambakkam reservoirs and other tanks for the past week because a buffer is needed in case of heavy rainfall,” says Srikanth.
Cyclone Michaung moving towards the Andhra Pradesh coast is another reason why water levels have receded in Chennai fairly quickly compared to 2015, points out Srikanth. “The high tides caused by the cyclone prevented water from the rivers and canals from draining into the sea. But when the cyclone moved towards Andhra, the water receded,” he says.