Early northeast monsoon onset creates ‘triple whammy’ in South India
The northeast monsoon began earlier this year, at least four days earlier in Tamil Nadu for the second consecutive year. Last year, this phase of the monsoon ended with the state recording 33% more rain than its long-term average, and forecasters expect this year to be the same.
Historically, policymakers and State officials have consistently interpreted extreme rainfall as positive. Climate change complicates this calculation because, while rainfall amounts increase, they are often concentrated in short, localized bursts, often delivering extremely large amounts of water to places that cannot fully absorb them. As a result, it may be time to rethink the idea that “excess is good.”
In urban areas, concrete and asphalt paved surfaces prevent the absorption of heavy rainfall, resulting in rapid runoff that strains drainage systems, resulting in flash floods, inundation of low-lying areas, property damage, and transportation disruption. Like during Cyclone Michaung and Tamil Nadu in 2023, urban power authorities also tend to cut power supply in such cases, citing loose cables. The large volume of water can also lead to sewer overflows, where untreated wastewater is discharged into streets and puddles, causing significant health and environmental hazards.
The sensitivity of the agricultural sector to extreme rainfall is well known: waterlogged soil smothers plant roots, washes out seeds and young crops, depletes nutrient-rich topsoil over time, and ultimately loses its long-term productivity. Too much moisture can also facilitate the spread of fungal diseases and pests that damage crops and reduce yields, leading to significant financial losses for farmers. Intense eruptions can also cause fertilizers, pesticides, and other agricultural residues to be washed into water bodies, including reservoirs, deteriorating 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 scrub typhus.
Prolonged rainfall also raises the water table, which is the level at which the soil is saturated with water. Persistently high water tables can compromise the stability of building foundations, roads and other infrastructure; It can also put stress on basement walls, causing cracks, leaks, and mold growth. Saturated soil also loses its load-bearing capacity and can cause foundations to shift or settle, potentially causing significant structural damage over time.
The cumulative effect of these problems leads to significant economic and social costs. Damage to buildings, public infrastructure and farmland requires significant investment in repair and reconstruction solutions. Disruptions in workplaces and transportation networks disrupt economic activities. Floods and landslides can also displace communities, injure and even kill people if they are particularly vulnerable. The psychological impact on the affected population, including stress and anxiety, is another important and often overlooked consequence.
Tamil Nadu also needs to take into account the Kerala factor in particular. The two states receive rainfall from two different monsoon patterns: Kerala’s primary rainfall 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. A major problem arises when these monsoon periods overlap or when both States experience heavy rainfall simultaneously. This is currently the case for the early onset of the northeast monsoon.
At the center of the issue is the Mullaperiyar Dam in Kerala’s Idukki district, operated by the Tamil Nadu government to divert water to irrigate farmland in Theni, Madurai, Dindigul and other districts. As a result, there is a ‘direct’ link between rainfall in Kerala’s catchments and water levels in Tamil Nadu’s river systems.
When the catchments of the Mullaperiyar Dam receive heavy rainfall, the reservoir fills quickly. To ensure the safety of the dam and manage rising water levels, Tamil Nadu authorities had to open the shutters of the dam, which released significant amounts of water downstream. The released water flows in two directions and risks creating a double whammy. Some of it flows down the Periyar River in Kerala, potentially inundating low-lying areas of Idukki district and creating an interstate problem, while the main flow is diverted to Tamil Nadu’s Vaigai Dam. And this influx could come as Tamil Nadu’s own rivers and reservoirs are already swollen due to the ongoing northeast monsoon.
This simultaneous flow transforms Kerala’s “excess” water from a potential resource to an immediate flood risk for Tamil Nadu. Instead of just managing rainwater falling within its borders, Tamil Nadu also has to manage a huge and concentrated flow from its neighbour. The government is currently keeping all 13 shutters of the Mullaperiyar Dam open and releasing thousands of cusecs of water to make room for the incessant influx. As a result, both farmland and residential areas in Theni have already been flooded, even as the region suffers from its own monsoon rains.
For these reasons, it may be time for other States like it, including Tamil Nadu and Kerala, to rethink the notion of “excess is better” in the face of rainfall.
It was published – 20 October 2025 14:17 IST
