The Northeast Monsoon over Tamil Nadu started earlier this year and for the second year at least four days early. Last year, this monsoon phase ended with the state receiving 33% more rainfall than the long-term average, and forecasters expect the same to happen this year.
Historically, politicians and government agencies have consistently interpreted excess rainfall as positive. Climate change complicates this calculation because, while rainfall volumes are increasing, they are often concentrated in short and localized bursts that deliver too much water to places that often cannot fully absorb it. As a result, it may be time to rethink the idea that “excess is good.”
In urban areas, concrete and asphalt paved surfaces prevent them from absorbing heavy rainfall, leading to rapid runoff that overwhelms sewer systems, resulting in flash floods, inundation of low-lying areas, property damage, and traffic disruption. Like during Cyclone Michaung and Tamil Nadu in 2023, city power authorities are also prone to cut off power supply due to loose cables in such circumstances. The sheer volume of water can also lead to sewage overflows, where untreated sewage is released into streets and waterways, posing significant health and environmental risks.
The vulnerability of the agricultural sector to excessive rainfall is well known: waterlogged soil suffocates plant roots, washes out seeds and young crops, over time the nutrient-rich topsoil is washed away and eventually loses its long-term fertility. Too much moisture can also facilitate the spread of fungal diseases and pests that devastate crops and undermine yield, leading to significant financial losses for farmers. Intense explosions can also wash fertilizers, pesticides, and other agricultural residues into bodies of water, including reservoirs, and degrade water quality. Finally, stagnant water becomes a breeding ground for mosquitoes, increasing the risk of vector-borne diseases such as malaria and dengue fever, and zoonotic diseases such as leptospirosis, Japanese encephalitis and typhus.
Long periods of rain also raise the water table, which is the level below which the soil is saturated with water. And persistently high groundwater levels can threaten the stability of building foundations, roads and other infrastructure; it can also put pressure on basement walls, leading to cracks, leaks and mold growth. Saturated soil also loses its bearing capacity and causes the foundation to shift or settle, which can lead to significant structural damage over time.
The cumulative impact of these problems translates into significant economic and social costs. Damage to buildings, public infrastructure and agricultural land requires significant investment in repairs and reconstruction. Disruption of businesses and transport networks hampers economic activity. Floods and landslides can also displace communities, injure and even kill people if they are particularly vulnerable. Another significant and often overlooked consequence is the psychological toll on the affected population, including stress and anxiety.
Tamil Nadu in particular has to consider the Kerala factor as well. The two states receive rain from two different monsoon patterns: Kerala’s primary rainy season is the southwest monsoon from June to September, while Tamil Nadu receives most of its rain during the northeast monsoon from October to December. An important problem arises when these monsoon seasons overlap or when both states experience intense rainfall at the same time. This is currently the case with the early onset of the Northeast Monsoon.
At the heart of the problem is the Mullaperiyar dam, which, though located in Idukki district of Kerala, is operated by the Tamil Nadu government to divert water for irrigation of agricultural land in Theni, Madurai, Dindigul and other districts. As a result, there is a “direct” link between rainfall in the Kerala watersheds and water levels in Tamil Nadu’s river systems.
When the Mullaperiyar dam catchment receives heavy rainfall, the reservoir fills up quickly. To ensure the safety of the dam and manage the rising water level, the Tamil Nadu authorities are forced to open the dam’s floodgates, releasing a significant volume of water downstream. The released water flows in two directions and risks creating a double whammy. One part flows down the Periyar River in Kerala, potentially flooding the low-lying areas of Idukki district and creating an inter-state problem, while the primary flow is diverted to the Vaigai Dam in Tamil Nadu. And this influx may come just as Tamil Nadu’s rivers and reservoirs are already high from the ongoing Northeast Monsoon.
This current influx thus turns Kerala’s “surplus” water from a potential resource to an imminent flood risk for Tamil Nadu. Instead of just managing the rainwater falling within its own borders, Tamil Nadu also has to manage the massive, concentrated inflow from its neighbour. The state is currently keeping all 13 sluices of the Mullaperiyar dam open and releasing thousands of cusecs of water to make room for the constant inflow. As a result, both agricultural land and residential areas in Theni are already submerged, even as the district is battered by its own monsoon rains.
For these reasons, perhaps the time has come for Tamil Nadu and other similar states, including Kerala, to rethink the notion of “excess is good” in the face of rains.
Published – 20 October 2025 14:17 IST
