The northeast monsoon has kicked in early this year, and at least four days sooner for the second year running, over Tamil Nadu. Last year, this phase of the monsoon ended with the State recording 33% more rain than the long-period average, and forecasters expect this year to go the same way as well.
Historically, policymakers and State authorities have consistently interpreted excess rain as a positive. Climate change is complicating this calculus because while rainfall volumes increase, they’re often concentrated in short and localised bursts, delivering over-large quantities of water in places that often can’t absorb them in full. As a result, it might be time to reconsider the idea that “excess is good”.
In urban areas, surfaces paved with concrete and asphalt keep them from absorbing heavy rainfall, leading to rapid runoff that overwhelms drainage systems, leading in turn to flash floods, low-lying areas being inundated, damage to property, and disrupted transportation. As during Cyclone Michaung and Tamil Nadu in 2023, urban power authorities are also prone to cutting power supply in such circumstances citing loose cables. The sheer volume of water can also lead to sewage overflows, where untreated wastewater is discharged into streets and waterbodies, unleashing significant health and environmental hazards.
The agricultural sector’s vulnerability to excessive rainfall is well-known: waterlogged soil suffocates plant roots, washes away seeds and young crops, sheds the nutrient-rich topsoil over time, and ultimately loses its long-term fertility. Too much moisture can also ease the spread of fungal diseases and pests that devastate crops and undercut yield, leading to significant financial losses for farmers. Intense bursts can also wash fertilizers, pesticides, and other agricultural debris into waterbodies, including reservoirs, degrading 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 like leptospirosis, Japanese encephalitis, and scrub typhus.
Prolonged periods of rainfall also raise the water table, which is the level below which the ground is saturated with water. And a persistently high water table can compromise the stability of building foundations, roads, and other infrastructure; it can also exert pressure on basement walls, leading to cracks, leaks, and the growth of mold. Saturated soil also loses its load-bearing capacity and causes foundations to shift or settle, potentially leading to significant structural damage over time.
The cumulative impact of these issues translates to significant economic and social costs. Damage to buildings, public infrastructure, and agricultural land warrants substantial investments in repair and rebuilding solutions. Disruptions to businesses and transport networks hamper economic activity. Flooding and landslips can also displace communities, injure people, and even kill them if they’re particularly vulnerable. The psychological toll on affected populations, including stress and anxiety, is another significant, and often overlooked, consequence.
Tamil Nadu in particular needs 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 whereas Tamil Nadu receives most of its rain during the northeast monsoon from October to December. An important problem arises when these monsoon periods overlap or when both States experience intense rainfall simultaneously. This is currently the case with the early onset of the northeast monsoon.
At the heart of the issue is the Mullaperiyar Dam, which, while it’s located in Kerala’s Idukki district, is operated by the Tamil Nadu government to divert water to irrigate farmland in Theni, Madurai, Dindigul, and other districts. There is as a result a ‘direct’ link between the rainfall in Kerala’s catchment areas and the water levels in Tamil Nadu’s river systems.
When the catchment areas of the Mullaperiyar Dam receive heavy rainfall, the reservoir fills up rapidly. To ensure the dam’s safety and to manage the rising water levels, Tamil Nadu’s authorities are compelled to open the dam’s shutters, releasing a significant volume of water downstream. The released water flows in two directions and risks creating a double whammy. One portion flows down the Periyar River within Kerala, potentially flooding the low-lying areas of Idukki district and creating an inter-State issue while the primary flow is diverted to Tamil Nadu’s Vaigai Dam. And this influx may arrive precisely when Tamil Nadu’s own rivers and reservoirs are already swollen from the ongoing northeast monsoon.
This simultaneous influx thus turns Kerala’s “excess” water from a potential resource into an immediate flood risk for Tamil Nadu. Instead of just managing the rainwater falling within its own borders, Tamil Nadu must also handle a massive, concentrated inflow from its neighbour. The State is currently keeping all 13 shutters of the Mullaperiyar Dam open, releasing thousands of cusecs of water in order to make room for the incessant influx. As a result, both farmland and residential areas in Theni are already submerged even as the district is being battered by its own monsoon rains.
For these reasons, it may be time for Tamil Nadu and other States like it, including Kerala, to reconsider the “excess is good” notion vis-à-vis rainfall.
Published – October 20, 2025 02:17 pm IST
