Introduction Fathom’s Japan Flood Map, Fathom-Japan, signals the next generation of flood data for Japan, applying unique algorithms, alongside leading modelling techniques and research. A rich body of high-quality observational data combined with the latest climate data, results in a sophisticated model that can provide confident estimations of present and future risk

Product key features


Resolution – 10 meter resolution.


3 time horizonsUtilising D4PDF ensemble of climate models to produce updated 2020, 2035 and 2050 climate states.


11 return periods – ranging from 1:5 year to 1:2500 year. Return periods can be categorised to suit your risk appetite.


Fluvial, pluvial & coastal floodingAssess the impact of multiple flood types.


Terrain dataIncorporates the latest LiDAR data, in addition to other terrain and hydrography datasets.


Flood Defences – Flood defences are explicitly built-in using a new levee detection algorithm.

About the model Japan possesses one of the most complex river infrastructures in the world, owing to a combination of unique hydrology and extensive anthropogenic intervention

Fathom represents every river channel in Japan, regardless of size and complexity.

We utilise detailed river network maps derived from Yamazaki’s Flow Direction Map (2018), a 1 arc-second national hydrology dataset developed by the University of Tokyo and Kyoto University. The dataset uses the National Elevation Dataset and the Water Map from the Geospatial Information Authority of Japan (GSI). When applying this data alongside Fathom’s dynamic solver, we are able to define channels in a much more accurate and realistic way.

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Tokyo 1000 year fluvial flood event (undefended).
Tokyo 250 year fluvial flood event (undefended).
Tokyo 5 year fluvial flood event (undefended).
Climate change

Anthropogenic global warming is increasing the frequency and severity of flood events

Fathom’s Japan Flood Map produces flood hazard data for present day, 2035 and 2050 time horizons to offer users a holistic view of hazard.

These horizons have been underpinned by data from the D4PDF ensemble of climate models and simulate the 4.5 Regional Concentration Pathway (RCP) trajectory.

A 2°C warmer world steady state projection was incorporated within Fathom-Japan’s hazard layers to estimate flood hazard at 2035 and 2050.

Following analysis undertaken on Fathom-Japan’s future scenarios, our researchers estimate a 1.93°C increase in Japan’s temperature by 2050.

Comparison of a Osaka 1 in 100 year undefended coastal flood event. Blue - present day. Red - 2050.

Research and validation Fathom’s Japan Flood Map benefits from an impressive portfolio of award winning research and methodologies spanning two decades

The methodologies implemented within Fathom-Japan have undertaken extensive validation. This research, has been published in leading peer-reviewed journals and has provided continuous validation to Fathom’s unique flood modelling techniques.

Working alongside academic partners, Fathom has ensured that a broad range of expertise and data has been considered when developing Fathom-Japan. This includes the use of data from the Global Hydrodynamics Lab, which is part of the U-Tokyo Global Hydrology Group in the Institute of Industrial Science at the University of Tokyo.

Our collaboration is part of a long-standing relationship that Fathom has with researchers from the University of Tokyo, with whom they have co-authored numerous papers. You can access this research here.

Contact us Find out more about Fathom-Japan.