The northeast monsoon has arrived ahead of schedule this year in Tamil Nadu, marking the second consecutive year of early onset, by at least four days. Last year, this monsoon period resulted in 33% more rainfall than the long-term average for the state, and weather forecasters anticipate a similar trend for the current year.
Traditionally, abundant rainfall has been viewed positively by policymakers and state officials. However, climate change is altering this perspective. While overall rainfall amounts may be rising, the precipitation often comes in short, localized, and intense downpours. These overwhelming volumes of water frequently exceed the absorption capacity of affected areas, prompting a necessary re-evaluation of the long-held belief that ‘more rain is always better’.
Urban environments, with their extensive concrete and asphalt surfaces, struggle to absorb heavy rainfall. This leads to rapid runoff that overwhelms drainage systems, causing flash floods, inundating low-lying regions, damaging property, and disrupting transportation. Experiences, such as during Cyclone Michaung in Tamil Nadu in 2023, show that urban power agencies often cut electricity due to concerns about loose cables. Moreover, the massive influx of water can result in sewage overflows, releasing untreated wastewater into streets and natural water bodies, posing serious health and environmental risks.
Agriculture is particularly susceptible to excessive rain. Waterlogged soil can suffocate plant roots, wash away newly sown seeds and young plants, and erode vital, nutrient-rich topsoil over time, reducing long-term soil fertility. Excessive moisture also fosters the proliferation of fungal diseases and pests, which can decimate crops and severely impact yields, causing substantial financial hardship for farmers. Additionally, intense downpours can carry fertilizers, pesticides, and other agricultural runoff into water bodies, including reservoirs, leading to significant water quality degradation. Lastly, stagnant water creates ideal breeding grounds for mosquitoes, elevating the risk of vector-borne illnesses like malaria and dengue, as well as zoonotic diseases such as leptospirosis, Japanese encephalitis, and scrub typhus.
Extended periods of heavy rainfall also cause the water table – the underground level where the ground is fully saturated with water – to rise. A consistently high water table can undermine the stability of building foundations, roads, and other essential infrastructure. It can also exert considerable pressure on basement walls, resulting in cracks, leaks, and the development of mold. Furthermore, saturated soil loses its ability to support weight, potentially causing foundations to shift or settle, which can lead to severe structural damage over time.
The combined effects of these challenges result in considerable economic and social burdens. Repairs and reconstruction of damaged buildings, public infrastructure, and agricultural lands require substantial financial investment. Economic activity is hindered by disruptions to businesses and transportation systems. Moreover, floods and landslides can force communities to evacuate, cause injuries, and even fatalities, especially among vulnerable populations. The emotional and psychological impact, including stress and anxiety, is a profound and frequently underestimated consequence for those affected.
For Tamil Nadu, the situation is further complicated by its proximity to Kerala. These two states experience distinct monsoon patterns: Kerala primarily gets its rain from the southwest monsoon between June and September, while Tamil Nadu relies on the northeast monsoon from October to December. A significant issue arises when these two monsoon periods coincide or when both states simultaneously receive intense rainfall, precisely the scenario unfolding with the early arrival of the northeast monsoon.
Central to this challenge is the Mullaperiyar Dam. Although situated in Kerala’s Idukki district, it is managed by the Tamil Nadu government, which uses it to supply irrigation water to agricultural areas in Theni, Madurai, Dindigul, and other regions. Consequently, there’s a direct correlation between rainfall in Kerala’s catchment zones and the water levels within Tamil Nadu’s river systems.
Heavy rainfall in the Mullaperiyar Dam’s catchment areas causes its reservoir to fill up quickly. To maintain the dam’s structural integrity and control rising water levels, Tamil Nadu authorities must open the dam’s shutters, discharging a substantial amount of water downstream. This released water poses a dual threat. Part of it flows into Kerala’s Periyar River, potentially flooding Idukki district’s low-lying areas and triggering an inter-state concern. The main flow, however, is diverted to Tamil Nadu’s Vaigai Dam, and this influx can arrive exactly when Tamil Nadu’s own rivers and reservoirs are already overflowing from its ongoing northeast monsoon.
This synchronized deluge transforms Kerala’s surplus water from a potential asset into an immediate flood threat for Tamil Nadu. Rather than simply managing rainfall within its own boundaries, Tamil Nadu is forced to contend with a massive, concentrated water inflow from a neighboring state. Currently, all 13 shutters of the Mullaperiyar Dam are open, releasing thousands of cusecs of water to accommodate the continuous inflow. Consequently, both agricultural lands and residential zones in Theni are already underwater, even as the district endures its own monsoon downpours.
Considering these critical factors, it appears to be a crucial moment for Tamil Nadu and other states facing similar challenges, including Kerala, to critically re-evaluate the perception that “excess rainfall” is inherently beneficial.