Fastflood.org, an open-source super-fast flood model in the browser

Flood modelling, particularly for urban contexts, often suffers from the long computation time and detailed data requirements. Real-time forecasting requires fast, data-efficient tools. A recent break-through in rapid flood simulation has allowed us to develop www.fastflood.org, an open-source platform for near-instant fully spatial flood prediction. It uses the fast sweeping method for elevation model correction, flow accumulation, and estimation of steady-state discharge. Afterwards, a compensated partial steady state is estimated through catchment characteristics and a flood depth field is iteratively back-calculated. We will show that our method, in various real-world tests, achieves over 97% accuracy compared to traditional models in flood extent modelling, while obtaining a speed increase of over 1500 times. Together with recently published global datasets on elevation and land cover, the web-based tool allows for rapid setup and simulation of flood scenarios. Due to the speed of the method, editing of risk-reducing measures (reservoirs, barriers, channel alterations) can be carried out with direct feedback on the consequences for small to medium sized areas. Testing on flash and fluvial flood events show very good promise for early warning methods by linking the flood simulation technique with weather forecasts in real-time. Finally, by employing recent IT technologies such as web-assembly, the model can run completely on the user’s machine, allowing for a sustainable, free model.