Perspectives on Open Access High Resolution Digital Elevation Models to Produce Global Flood Hazard Layers

Abstract

Global flood hazard models have recently become a reality thanks to the release of open access global digital elevation models, the development of simplified and highly efficient flow algorithms, and the steady increase in computational power. In this commentary we argue that although the availability of open access global terrain data has been critical in enabling the development of such models, the relatively poor resolution and precision of these data now limit significantly our ability to estimate flood inundation and risk for the majority of the planet's surface. The difficulty of deriving an accurate "bare-earth" terrain model due to the interaction of vegetation and urban structures with the satellite-based remote sensors means that global terrain data are often poorest in the areas where people, property (and thus vulnerability) are most concentrated. Furthermore, the current generation of open access global terrain models are over a decade old and many large floodplains, particularly those in developing countries, have undergone significant change in this time. There is therefore a pressing need for a new generation of high resolution and high vertical precision open access global digital elevation models to allow significantly improved global flood hazard models to be developed.Keywords: global flood modeling, DEM, Hydraulic modeling, remote sensing of environment, hazard modeling Around the turn of the millennium, high quality two dimensional hydraulic models capable of simulating the dynamics of flood inundation became a reality at the reach scale as a result of faster computers, improved algorithms (Bates and De Roo, 2000;Bradford and Sanders, 2002;Bradbrook et al., 2004), and new forms of rapidly-collected remotely sensed digital elevation models (DEMs; Marks and Bates, 2000;Cobby et al., 2001;Bates et al., 2003;Bates, 2004;Sanders, 2007). Of particular value to hydraulic modelers in developed countries was the commencement of routine LIDAR collection due to its high horizontal and vertical precision and accuracy, its ability to penetrate vegetation cover and its reduced susceptibility to scatter and shadowing relative to other forms of remotely sensed elevation data such as Interferometric Synthetic Aperture Radar (InSAR;Bates, 2004). These three key properties made it ideally suited to the creation of "bare-earth" Digital Terrain Models (DTMs), a type of DEM in which surface features such as vegetation and built structures are removed to leave, as the name suggests, a three dimensional representation of the bare-earth surface. Such data are ideally suited for the purposes of flood hazard simulation using hydraulic models, and form the basic datasets from which developed world flood hazard layers, such as the Federal Emergency Management Agency (FEMA) flood maps in the USA, and the Environment Agency Flood Maps in the UK, are produced.

A high‐accuracy map of global terrain elevations

“…Precise representation of global terrain is a fundamental goal of geodetic survey, and essential for studies including topography classification for earthquake motion assessment [ Hough et al ., ], flood inundation modeling [ Yamazaki et al ., ; Sampson et al ., ], global wetland carbon dynamics [ Laudon et al ., ], soil erosion and sediment yield prediction [ de Vente et al ., ], and water mapping by remote sensing [ Pekel et al ., ]. While high‐accuracy airborne digital elevation models (DEMs) are available in developed countries, many regions of the world still rely on spaceborne DEMs.…”

Impacts of spatial resolution and representation of flow connectivity on large-scale simulation of floods

“…With the increasing computational power, improved computation algorithms, and availability of finer spatial datasets, it is now possible to model large-to global-scale floods in finer detail (Bierkens, 2015;Trigg et al, 2016). It is envisioned that the development and application of global models to finer spatial resolutions will lead to improvements in their accuracy and operational applicability (Wood et al, 2011;Lehner and Grill, 2013;Bierkens, 2015;Sampson et al, 2016). With respect to surface water and flood modeling, Wood et al (2011) have highlighted the need for high spatial resolution to capture topographical controls which are critical for reliable and robust simulation of flood inundation.…”

Evaluating Conveyance-Based DEM Correction Technique on NED and SRTM DEMs for Flood Impact Assessment of the 2010 Cumberland River Flood

“…The error in channel slope in the upper reach (please refer to Table 1) could be a factor causing this error. This is because gravity and hydraulic connectivity move the water downwards both in the model and in reality [13]. Additionally, the base SRTM-derived simulation was not possible in the pre-flood window (prior to 1 May).…”

“…The primary sources of error in a spaceborne DEM (i.e., SRTM) are speckle noise, stripe noise, absolute bias, and tree height bias, in addition to the inability of mapping river bathymetry [11][12][13][14]. The first four error sources primarily affect hydraulic connectivity within the floodplain, and inaccurate river bathymetry affects the river conveyance.…”

“…This is often supplemented by overlaying surveyed river cross sections on a reach scale. However, this approach is unfeasible on a regional to global scale [13]. There have been multiple methods in practice to correct DEM for better representation of river conveyance in the absence of surveyed cross sections.…”