Geomorphic Flood Mapping & the Geomorphic Flood Index
A terrain-based, physically-grounded framework for rapid and cost-effective delineation of flood-prone areas—from ungauged basins to continental-scale applications.
Terrain-Informed Flood Susceptibility
Geomorphic approaches exploit terrain information derived from Digital Elevation Models (DEMs) to delineate flood-prone areas. These methods provide robust and scalable alternatives to hydraulic models, particularly in ungauged basins and data-scarce environments where hydrological records, cross-section surveys, and high-resolution hydraulic simulations are unavailable.
The Geomorphic Flood Index (GFI) represents a key advancement in terrain-based flood mapping. It links topographic attributes with hydraulic scaling relationships, comparing the expected flood water level at the nearest channel element with the local elevation difference. Points whose elevation falls below the estimated flood stage are classified as flood-prone.
First proposed in 2011 by Salvatore Manfreda and collaborators, the GFI framework has since been validated across multiple continents, extended to coastal environments, and released as freely available software. The latest version, GFI 2.0, introduces a Hierarchical River-First Update (River-to-Confluence mapping) that accounts for downstream backwater effects and confluence influences, significantly improving spatial accuracy in complex drainage networks.
hrEstimated flood water depth at the nearest river element, via hydraulic scaling: hr = a · ArnHElevation difference between the terrain point and the nearest channel element along the hydrological flow pathGFIPositive values → flood susceptibility; negative → safe terrain. A threshold τ is calibrated via ROC analysis on a reference flood map.
a = e−τ (calibration coefficient)
WD = max(0, hr − H) (water depth)
From DEM to Flood Map
DEM Acquisition & Pre-processing
Obtain a DEM (SRTM, LiDAR, TanDEM-X). Fill sinks, resolve flat areas, assign drainage directions.
Drainage Network Extraction
Compute flow accumulation and delineate the channel network using area–slope thresholds (ASk method).
GFI Computation
For each cell, estimate hr via hydraulic scaling and compute ln(hr/H). In v2.0, downstream flood depths propagate to upstream segments via River-to-Confluence mapping.
Binary Classification & Calibration
Calibrate the threshold τ against a reference flood map (≥ 2 % of basin area). Optimise via ROC analysis (maximise AUC).
Flood Susceptibility Output
Output a binary flood-prone/safe raster, continuous GFI and water depth grids, and performance metrics (AUC, FPR, FNR).
Tools & Software
All GFI tools are freely available under open-source licences.
MATLAB-based toolbox implementing the full GFI pipeline with the new Hierarchical River-First Update (River-to-Confluence mapping). Accounts for confluence backwater effects, propagates downstream flood depths upstream, and outputs calibrated water-depth grids. Requires TopoToolbox v3; includes a Bradano River example DEM at 5 m resolution.
Navarro, J. S., Albertini, C., Zhuang, R., Chaturvedi, S., Pacia, F. D., Samela, C., & Manfreda, S. (2026). Geomorphic Flood Index (GFI) version 2.0 (2.0). Zenodo. doi:10.5281/zenodo.18903835
Open-source QGIS plugin (Geomorphic Flood Area tool) providing a user-friendly interface for flood-prone area delineation via the GFI binary classifier. Supports ESRI, HyGrid2k2 and TauDEM flow conventions. Outputs GFI rasters, normalised GFI (−1 to 1), binary flood maps, and performance metrics.
Samela, C., Albano, R., Sole, A. & Manfreda, S. (2018). A GIS Tool for Cost-Effective Delineation of Flood-Prone Areas. Comput. Environ. Urban Syst., 70, 43–52.
Publications
Peer-reviewed articles, datasets, and software related to the Geomorphic Flood Index.
@article{manfreda2026gfi2,
title = {{Geomorphic Flood Index 2.0: Enhanced Tools for
Delineating Flood-Prone Areas in Data-Scarce Regions}},
author = {Manfreda, Salvatore and {Saavedra Navarro}, J. and
Albertini, C. and Zhuang, R. and Pacia, F. D. and
Chaturvedi, S. and Samela, Caterina},
journal = {SSRN Preprint},
year = {2026},
doi = {10.2139/ssrn.5461780}
}@article{albertini2024rf,
title = {{Assessing Multi-source Random Forest Classification and
Robustness of Predictor Variables in Flooded Areas Mapping}},
author = {Albertini, C. and Gioia, A. and Iacobellis, V. and
Petropoulos, G. P. and Manfreda, Salvatore},
journal = {Remote Sensing Applications: Society and Environment},
year = {2024},
doi = {10.1016/j.rsase.2024.101239}
}@article{albertini2022surface,
title = {{Detection of Surface Water and Floods with Multispectral Satellites}},
author = {Albertini, C. and Gioia, A. and Iacobellis, V. and Manfreda, S.},
journal = {Remote Sensing},
volume = {14},
pages = {6005},
year = {2022},
doi = {10.3390/rs14236005}
}@article{albertini2021coastal,
title = {{Flood-Prone Areas Delineation in Coastal Regions
Using the Geomorphic Flood Index}},
author = {Albertini, C. and Miglino, D. and Iacobellis, V. and
De Paola, F. and Manfreda, S.},
journal = {Journal of Flood Risk Management},
pages = {e12766},
year = {2021},
doi = {10.1111/jfr3.12766}
}@article{albano2020romania,
title = {{Large Scale Flood Risk Mapping in Data Scarce Environments:
An Application for Romania}},
author = {Albano, R. and Samela, C. and Craciun, I. and Manfreda, S.
and Adamowski, J. and Sole, A. and Sivertun, A. and Ozunu, A.},
journal = {Water},
volume = {12},
number = {6},
pages = {1834},
year = {2020},
doi = {10.3390/w12061834}
}@article{tavarescosta2020,
title = {{Predictive Modelling of Envelope Flood Extents Using Geomorphic
and Climatic-Hydrologic Catchment Characteristics}},
author = {{Tavares da Costa}, R. and Zanardo, S. and Bagli, S. and
Hilberts, A. G. J. and Manfreda, S. and Samela, C. and
Castellarin, A.},
journal = {Water Resources Research},
year = {2020},
doi = {10.1029/2019WR026453}
}@article{manfreda2019depth,
title = {{A DEM-based Method for a Rapid Estimation of Flood Inundation Depth}},
author = {Manfreda, Salvatore and Samela, Caterina},
journal = {Journal of Flood Risk Management},
volume = {12},
number = {S1},
pages = {e12541},
year = {2019},
doi = {10.1111/jfr3.12541}
}@article{tavarescosta2019web,
title = {{A Web Application for Hydrogeomorphic Flood Hazard Mapping}},
author = {{Tavares da Costa}, R. and Manfreda, S. and Luzzi, V. and
Samela, C. and Mazzoli, P. and Castellarin, A. and Bagli, S.},
journal = {Environmental Modelling and Software},
year = {2019},
doi = {10.1016/j.envsoft.2019.01.010}
}@article{samela2018gis,
title = {{A GIS Tool for Cost-Effective Delineation of Flood-Prone Areas}},
author = {Samela, Caterina and Albano, Raffaele and
Sole, Aurelia and Manfreda, Salvatore},
journal = {Computers, Environment and Urban Systems},
volume = {70},
pages = {43--52},
year = {2018},
doi = {10.1016/j.compenvurbsys.2018.01.013}
}@article{manfreda2018advances,
title = {{Advances in Large Scale Flood Monitoring and Detection}},
author = {Manfreda, S. and Samela, C. and Refice, A. and
Tramutoli, V. and Nardi, F.},
journal = {Hydrology},
volume = {5},
number = {3},
pages = {49},
year = {2018},
doi = {10.3390/hydrology5030049}
}@article{samela2017geomorphic,
title = {{Geomorphic Classifiers for Flood-Prone Areas Delineation
for Data-Scarce Environments}},
author = {Samela, Caterina and Troy, T. J. and Manfreda, Salvatore},
journal = {Advances in Water Resources},
volume = {102},
pages = {13--28},
year = {2017},
doi = {10.1016/j.advwatres.2017.01.007}
}@article{samela2017data,
title = {{100-Year Geomorphic Flood-Prone Areas for the Continental U.S.}},
author = {Samela, C. and Manfreda, S. and Troy, T. J.},
journal = {Data in Brief},
volume = {12},
pages = {203--207},
year = {2017},
doi = {10.1016/j.dib.2017.03.044}
}@article{samela2016africa,
title = {{DEM-Based Approaches for the Delineation of Flood Prone Areas
in an Ungauged Basin in Africa}},
author = {Samela, C. and Manfreda, S. and De Paola, F. and
Giugni, M. and Sole, A. and Fiorentino, M.},
journal = {Journal of Hydrologic Engineering},
volume = {21},
number = {2},
year = {2016},
doi = {10.1061/(ASCE)HE.1943-5584.0001272}
}@article{manfreda2015binary,
title = {{Flood-Prone Areas Assessment Using Linear Binary Classifiers
Based on Flood Maps Obtained from 1D and 2D Hydraulic Models}},
author = {Manfreda, S. and Samela, C. and Gioia, A. and Consoli, G. and
Iacobellis, V. and Giuzio, L. and Cantisani, A. and Sole, A.},
journal = {Natural Hazards},
volume = {79},
number = {2},
pages = {735--754},
year = {2015},
doi = {10.1007/s11069-015-1869-5}
}@article{manfreda2014investigation,
title = {{Investigation on the Use of Geomorphic Approaches for the
Delineation of Flood Prone Areas}},
author = {Manfreda, S. and Nardi, F. and Samela, C. and Grimaldi, S.
and Taramasso, A. C. and Roth, G. and Sole, A.},
journal = {Journal of Hydrology},
volume = {517},
pages = {863--876},
year = {2014},
doi = {10.1016/j.jhydrol.2014.06.009}
}@article{manfreda2011detection,
title = {{Detection of Flood Prone Areas Using Digital Elevation Models}},
author = {Manfreda, Salvatore and {Di Leo}, M. and Sole, A.},
journal = {Journal of Hydrologic Engineering},
volume = {16},
number = {10},
pages = {781--790},
year = {2011},
doi = {10.1061/(ASCE)HE.1943-5584.0000367}
}Downloads
Publications, datasets, and toolboxes—all freely available.
Attachments
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Detection of Flood Prone Areas using Digital Elevation Models
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Geomorphic classifiers for flood-prone areas delineation for data-scarce environments
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A GIS tool for cost-effective delineation of flood-prone areas
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A digital elevation model based method for a rapid estimation of flood inundation depth
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DEM-based approaches for the delineation of flood prone areas in an ungauged basin in Africa
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Large Scale Flood Risk Mapping in Data Scarce Environments: An Application for Romania
-
Predictive modelling of envelope flood extents using geomorphic and climatic- hydrologic catchment characteristics
-
Investigation on the use of geomorphic approaches for the delineation of flood prone areas