KOLLAM: Floods of the scale Kerala witnessed in 2018 — earlier believed to occur only once in 150 years — could now hit every 25 years, a new study has found.
Analysing four decades of river flow data in Kerala, the study, carried out by researchers from the civil engineering department of TKM College of Engineering, Kollam, warns that the state’s current flood models underestimate real flood risk by up to 40%, leaving key infrastructure vulnerable as climate change intensifies.
The study notes that Kerala’s flood maps, dam safety norms and drainage design standards no longer reflect current rainfall patterns, explaining why towns go underwater even after moderate rainfall.
It warns that unless design standards are urgently updated, even routine monsoon spells could trigger severe flooding across both urban and rural regions.
The shift was identified using non-stationary flood frequency analysis — a method that accommodates climate variability linked to factors such as El Nino, the Indian Ocean Dipole (IOD) and the North Atlantic Oscillation (NAO). The team analysed 40 years of flood discharge records (1980-2019) from the Irrigation Design and Research Board.
Study: Flood designs need to evolve with climate reality
At the Muvattupuzha station, the 2018 flood discharge of 2,412 cubic metres per second — earlier estimated to occur once in 150 years — was recalculated to have a return period of just 25 years. At Thodupuzha, a 62-year event was shortened to 25 years, while at Kakkadassery, a 75-year event now has a return period of only 12 years. The study also found that the estimated magnitude of floods could increase by 29 to 40% when climate change vulnerability is factored in.
“Our infrastructure was built on the assumption that climate change would not occur, that climatic events such as temperature and lunar cycles would remain the same. But that isn’t the truth. Our bridges, dams, and drainage systems are in jeopardy as their capacity to handle sudden downpours is limited,” said professor Adarsh S, head of civil engineering department at the TKM College of Engineering, who led the study.
From Thiruvananthapuram to Kochi, waterlogging has become routine even after moderate rain. Researchers said this was because Kerala’s drainage network, culverts, and bridges were designed using a flood map that no longer reflects current rainfall patterns.
“Kerala receives over 80% of its annual rainfall in just four months and has faced major floods in 2018, 2019, 2020, and 2024. These back-to-back events show that floods are becoming more intense and frequent. If flood designs do not evolve with climate reality, the cost will be devastating,” the study noted. The study was carried out with assistance from the Core Research Grant under the Department of Science and Technology’s Science and Engineering Research Board. Professor Adarsh and research scholar Meera G Mohan were the team members. The results of their research have been published in journals such as Water Resources Management, Physics and Chemistry of the Earth, Theoretical and Applied Climatology, Water Security, and H2Open Journal.