Chennai: Rapid urban expansion, shrinking vegetation and water bodies, drainage gaps, and low-lying terrain contribute to flood risk, according to a University of Madras study. The city’s flood-risk hotspots include Velachery, Pallavaram, Chromepet and surrounding southern localities, parts of western Chennai, Koyambedu, Villivakkam and areas around Tondiarpet.The study found that between 2000 and 2024, Chennai’s built-up area grew 7.6%, vegetation cover declined 26.14% and water bodies shrank 22.54%.“Spatial analysis indicates that flood-prone areas are concentrated in low-lying coastal zones, western and southern peri-urban areas, and Adyar River floodplain, where urban expansion, high flow accumulation, and historical flood occurrences overlap,” said first author Rahul Debnath.The study found that roads and buildings replace permeable surfaces, reducing rainwater absorption and increasing surface runoff. Drainage gaps in western and southern peripheral areas overlap with recent urban expansion, suggesting infrastructure has not kept pace with development. Areas more than 1km from mapped stormwater drains were classified as having drainage gaps.Researchers analysed Landsat satellite imagery from five years, elevation data, India Meteorological Department rainfall records and historical flood locations using GIS and remote sensing. The study found that rainfall in 2015 exceeded its estimated 100-year return-period intensity, while the 2023 event was associated with a nearly 25-year return period.The authors recommend integrating land-use planning, terrain characteristics and historical flood records into flood-risk management. They also call for assessing drainage coverage and capacity to identify priority areas for intervention.Meanwhile, revenue administration and disaster management commissioner B Chandra Mohan said Tamil Nadu had identified around 1,030 locations with high or very high vulnerability and another 1,003 with moderate vulnerability, based on experience, forecasts and water-stagnation depth. Teams assessed vulnerable locations and prepared mitigation and response plans.“Each particular location now has a plan that is being used for mitigation. It has also got a response plan,” he said. These plans include water-level triggers for action and evacuation, specifying where people should be moved as water rises.While the study identified gaps in drainage coverage, the Greater Chennai Corporation (GCC) has expanded its stormwater drain network in recent years. Between 2022 and 2025, 1,144.5km of stormwater drains had been laid, according to the corporation.
