Abstract
This paper explores a method to combine the time and space continuity of a large-scale inundation model with discontinuous satellite microwave observations, for high-resolution flood hazard mapping. The assumption behind this approach is that hydraulic variables computed from continuous spatially-distributed hydrodynamic modeling and observed as discrete satellite-derived flood extents are correlated in time, so that probabilities can be transferred from the model series to the observations. A prerequisite is, therefore, the existence of a significant correlation between a modeled variable (i.e., flood extent or volume) and the synchronously-observed flood extent. If this is the case, the availability of model simulations over a long time period allows for a robust estimate of non-exceedance probabilities that can be attributed to corresponding synchronously-available satellite observations. The generated flood hazard map has a spatial resolution equal to that of the satellite images, which is higher than that of currently available large scale inundation models. The method was applied on the Severn River (UK), using the outputs of a global inundation model provided by the European Centre for Medium-range Weather Forecasts and a large collection of ENVISAT ASAR imagery. A comparison between the hazard map obtained with the proposed method and with a more traditional numerical modeling approach supports the hypothesis that combining model results and satellite observations could provide advantages for high-resolution flood hazard mapping, provided that a sufficient number of remote sensing images is available and that a time correlation is present between variables derived from a global model and obtained from satellite observations.
Highlights
In the framework of a comprehensive and standardized flood risk management at the global scale, the development of a remote sensing-based flood hazard mapping method is of primary interest.Hazard maps are needed to enhance flood preparedness at large scale and to improve the services provided for crisis response and mitigation
More details of the spatial inundation pattern are visible in the selected satellite image, whereas only the major body of the flood is captured by the model results
Such heterogeneity in the spatial scale introduces discrepancies and inaccuracies in the computation of correlation between the two datasets. This comparison shows that merging model results and remote sensing-derived observations allows generating flood hazard maps that have a resolution that is higher and arguably more accurate than what would be possible with the global model alone
Summary
In the framework of a comprehensive and standardized flood risk management at the global scale, the development of a remote sensing-based flood hazard mapping method is of primary interest.Hazard maps are needed to enhance flood preparedness at large scale and to improve the services provided for crisis response and mitigation. Pappenberger et al [5] estimated global flood hazard through a physical model cascade, here named PDWC2012, consisting of an atmospheric model linked to a coupled hydrologic-hydraulic model and forced with ERA-Interim reanalysed meteorological data. It performs continuous hydrologic and hydraulic simulations for the entire globe on a 25 km grid which is re-projected onto a 1 km grid to derive maps of higher resolution. As the use of the design hyetograph and/or the design hydrograph constitutes one of the main sources of uncertainty, in the recent literature the use of continuous hydrologic and hydraulic simulations has been introduced [7,8,9]
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