When Cyclone Ditwah made landfall on November 28 2025, Sri Lanka skilled one in all its deadliest environmental screw ups in fashionable historical past.
President Anura Kumara Dissanayake declared it the “largest and most challenging natural disaster in our history”. Torrential rains precipitated popular floods and landslides, resulting in greater than 350 showed deaths, loads lacking and over 1.4 million folks affected national.
Primary street and rail techniques have been bring to a halt, hydropower stations and water remedy vegetation failed, and hundreds of households have been pressured into emergency shelters. Reservoirs overflowed, riverbanks collapsed and communities close to the Mahaweli, Kelani, Malwathu Oya and Mundeni Aru river basins have been inundated inside hours.
Those weren’t random screw ups. They have been systemic. Most of the areas that flooded have been susceptible spaces adjoining to coastal lagoons and low-lying river plains. Cyclone Ditwah used to be no longer an anomaly. It uncovered the underlying fragilities of Sri Lanka’s current flood-management and drainage infrastructure.
This follows on from the devastating tropical cyclone in 1978 and the Boxing Day 2004 tsunami catastrophe. Fifty years in the past, flood infrastructure used to be no longer in a just right state. Vital enhancements haven’t been made since then, basically because of deficient city making plans.
Between 2018 and 2022, I labored with a world staff of coastal engineers, social scientists and coverage makers from academia and executive organisations in the United Kingdom, Australia and Sri Lanka. Our analysis undertaking fascinated with generating a brand new technology of compound flood danger maps, in accordance with pc modelling that considers the entire typhoon surge elements (surge, tide and sea point upward push) and the rainfall impact.
I led the hydrological modelling efforts for Sri Lanka – that specialize in how tropical-cyclone rainfall and typhoon surge mix to generate harmful flooding patterns for 3 susceptible towns: Batticaloa, Mullaitivu and Mannar. The staff labored with Sri Lanka’s Coast Conservation and Coastal Useful resource Control Division (CCD) to handle a vital query: How do typhoon surges from tropical cyclones have interaction with rainfall to supply excessive inland and coastal floods?
Thru research of historical cyclone tracks, we confirmed that Sri Lanka lies on the convergence of more than one typhoon pathways within the Bay of Bengal. That is why the rustic time and again suffers no longer most effective from rainfall-driven inundation but in addition from saltwater intrusion pushed deep inland via lagoons and estuaries.
My staff and I evolved the hydrologic fashion for Batticaloa, the usage of the Mundeni Aru river basin as a pilot case. We blended rainfall information, virtual terrain maps (that point out bushes, constructions, roads and naked land) and river-flow simulations to spot essentially the most susceptible communities relying at the topography. Low-lying settlements adjoining to the Batticaloa and Valachchenai lagoons have been specifically liable to tropical cyclone-induced flooding.
Streets flooded as Ditwah Cyclone hit Sri Lanka (November 30 2025).
Thamara Perera/Shutterstock
Equivalent modelling paintings used to be proposed for Mullaitivu and Mannar, each historical cyclone-landfall areas. Then again, COVID disrupted a lot of the deliberate in-country engagement, in-depth modelling and translation of findings into coverage equipment, growing a significant lag between medical insights and what making plans government are lately referencing.
Ditwah’s aftermath – breached embankments, energy screw ups, displaced households, submerged neighbourhoods – corresponds nearly precisely to the worst-case compound-flood situations proven by way of our information. Those don’t seem to be purely meteorological phenomena. They rely at the movement of water and land-based infrastructure.
Drainage networks nonetheless depend on old-fashioned ancient rainfall information. Coastal defences are constructed for typhoon surges of earlier many years. City construction continues to occupy herbal flood buffers akin to wetlands and lagoon edges. Vulnerability has change into bodily engineered into the panorama.
Proactive making plans
Operating with executive companies together with the CCD, the Met Place of business and the Crisis Control Centre, Sri Lanka can proactively combine compound-flood science into making plans and catastrophe risk-reduction methods.
This comprises generating up to date flood maps that seize rainfall, river movement, typhoon surge and sea-level-rise dynamics. Hydrological fashions may also be translated into operational equipment for nationwide and municipal making plans government.
Drainage and river-management techniques (akin to seasonal elimination of sand and particles) may also be redesigned with the longer term (no longer ancient) rainfall intensities in thoughts. Bettering early-warning techniques comes to incorporating more than one hazards and long-range state of affairs modelling may also be embedded into disaster-preparedness and land-use making plans.
Those measures allow policymakers, engineers and native administrations to make evidence-based choices that replicate accelerating climate-driven dangers moderately than out of date assumptions.
Cyclone Ditwah will have to mark a turning level. With the appropriate integration of science, making plans and governance, screw ups of this magnitude don’t need to change into inevitable hallmarks of Sri Lanka’s long run. And by way of aligning infrastructure and coverage with the actual hydrological dynamics of our converting weather, governments can higher offer protection to folks, setting and financial system from the storms but to come back.
