Bangkok’s two-day drainage workers’ strike turned a season of heavy rain into a rare test of the city’s home-grown flood measures, researchers said on Tuesday. Their study estimates that rain gardens, storage tanks and small canals maintained by residents reduced indoor flooding by 74% in 27 neighbourhoods when municipal crews were off duty.
The findings, published by the Siam Delta Institute in the Monsoon Cities Review, compare water levels and household reports across 79 neighbourhoods from 2022 to 2025. Researchers examined 14 major rain events, including one in August 2025 when 186 millimetres (7.3 inches) fell in 30 hours as 2,100 drainage workers walked out over delayed hazard allowances.
A strike becomes a field test
In the 27 neighbourhoods with local water-storage projects, an estimated 312 homes took water indoors during that storm, compared with 1,190 in similarly low-lying areas without them. Researchers say the systems held back about 3.8 million cubic metres of runoff and helped avoid 2.1 billion baht (about €55 million or $59 million) in household and shop damage.
“For the first time, we could see what these small projects do when the city’s normal response is unavailable,” said Élodie Ménard, the study’s lead author. The team combined rain-gauge readings, street-level water marks and interviews with 640 households; it said the results remained strong after accounting for differences in elevation and drainage access.
The strike began before dawn on 28 August, after talks over allowances stalled, and lasted 48 hours. Streets in several districts flooded, but residents in the study areas cleared small channels, opened storage gates and moved water from planted courtyards into tanks. No one was injured, and the report does not claim that local projects prevented flooding everywhere.
Small works, larger stakes
The study lands as governments face pressure to spend more on adapting to heat, floods and rising seas, while international negotiations over climate funding remain contentious. The authors argue that neighbourhood projects can deliver quickly for a fraction of the cost of major drainage works: the 27 areas spent a combined 164 million baht (about €4.3 million or $4.6 million) over four years.
Bangkok’s deputy drainage director, Devamany Sabki, said the city would seek 300 million baht (about €7.9 million or $8.4 million) in next year’s budget to expand the programme to 40 more neighbourhoods. “We cannot ask residents to replace the city’s drains,” Sabki said. “But we can give them tools that keep a bad night from becoming a lost season.”
The researchers caution that their study measured one unusually wet event and cannot show that community systems would withstand a longer storm or protect every home. Still, they estimate the projects cut floodwater entry by at least half in 11 of the 14 storms reviewed, and say the next step is to publish maps of suitable sites before the 2027 monsoon.
