Preprints
https://doi.org/10.5194/nhess-2021-136
https://doi.org/10.5194/nhess-2021-136

  17 May 2021

17 May 2021

Review status: this preprint is currently under review for the journal NHESS.

Global riverine flood risk – how do hydrogeomorphic floodplain maps compare to flood hazard maps?

Sara Lindersson1,2, Luigia Brandimarte3, Johanna Mård1,2, and Giuliano Di Baldassarre1,2 Sara Lindersson et al.
  • 1Centre of Natural Hazards and Disaster Science (CNDS), c/o Department of Earth Sciences, Uppsala University, 75236, 5 Uppsala, Sweden
  • 2Department of Earth Sciences, Uppsala University, 75236, Uppsala, Sweden
  • 3KTH – Royal Institute of Technology, 10044 Stockholm, Sweden

Abstract. Riverine flood risk studies require the identification of areas prone to potential flooding. This process can be based on either (hydrologically-derived) flood hazard maps or (topography-based) hydrogeomorphic floodplain maps. In this paper, we derive and compare riverine flood exposure from three global products: a hydrogeomorphic floodplain map (GFPLAIN) and two flood hazard maps (JRC and GAR). We find an average spatial agreement between these maps of around 30% at river basin level on a global scale. This agreement is highly variable across model combinations and geographic conditions, influenced by climatic humidity, river volume, topography, and coastal proximity. Contrary to expectations, the agreement between the two flood hazard maps is lower compared to their agreement with the hydrogeomorphic floodplain map. We also map riverine flood exposure for 26 countries across the Global South, by intersecting these maps with three human population maps (GHS, HRSL and WorldPop). The findings of this study indicate that hydrogeomorphic floodplain maps can be a valuable way of producing high-resolution maps of flood-prone zones to support riverine flood risk studies, but caution should be taken in regions that are dry, steep, very flat or near the coast.

Sara Lindersson et al.

Status: open (until 28 Jun 2021)

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Sara Lindersson et al.

Sara Lindersson et al.

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Short summary
Riverine flood risk assessments require the identification of areas prone to potential flooding. We find that (topography-based) hydrogeomorphic floodplain maps can in many cases be useful for riverine flood risk assessments, particularly where hydrologic data are scarce. For 26 countries across the Global South, we also demonstrate how dataset choice influences the estimated number of people living within flood-prone zones.
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