Nepal Flood maps: Fluvial Defended, Undefended and Pluvial for various return periods.

Please click the layers icon in the map area to select the type of flood and return period.

The data presented here show the modelled water depth for flood events of different return periods.  Both fluvial flooding (flooding from rivers) and pluvial flooding (local surface water flooding from extreme rainfall) have been simulated and can be displayed.  Depths are shown in meters.  Note that one would not expect all the displayed flooding to happen at the same time; rather, the data show the maximum water depth that would be expected if a flood event of the specified return period were occurring at that location.  Another way of expressing this is to say that the data show the probability of experiencing a given water depth within a single year; i.e. depths shown by the ‘1-in-100 year’ layer have a 1-in-100 (or 1%) chance of occurrence in any given year.

The data has been produced using the Fathom global flood hazard modelling framework (a development of Sampson et al., 2015 and Smith et al., 2015).  The model uses the MERIT global DEM and hydrography for elevation and river network data sources respectively (Yamazaki et al., 2017; Yamazaki et al., 2019).  The framework automatically constructs flood models across a specified region, using the two-dimensional shallow water equations to simulate the behavior of floodwaters during the modelled flood events.  The framework produces maps of flood depths at 3 arcsecond (~90m) spatial resolution for a specified range of return periods.  For a detailed technical description of the methods, please see the open-access academic papers listed below.

Given that the modelling framework used to create this data is semi-autonomous and uses data available at the regional to global scale, its accuracy is limited by the quality of this input data and the simplified range of processes it can represent.  While the data is suitable for providing guidance at the regional scale, it is not recommended to use the data for detailed local scale assessments or engineering purposes.  More details around appropriate use can be found in the user training documentation (link here).


Open access journal hyperlinks:

Sampson et al 2015

Smith et al 2015:

Yamazaki et al 2017:

Yamazaki et al 2019: