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

Abstract

Abstract. Global-scale river models (GRMs) are core tools for providing consistent estimates of global flood hazard, especially in data-scarce regions. Due to former limitations in computational power and input datasets, most GRMs have been developed to use simplified representations of flow physics and run at coarse spatial resolutions. With increasing computational power and improved datasets, the application of GRMs to finer resolutions is becoming a reality. To support development in this direction, the suitability of GRMs for application to finer resolutions needs to be assessed. This study investigates the impacts of spatial resolution and flow connectivity representation on the predictive capability of a GRM, CaMa-Flood, in simulating the 2011 extreme flood in Thailand. Analyses show that when single downstream connectivity (SDC) is assumed, simulation results deteriorate with finer spatial resolution; Nash-Sutcliffe efficiency coefficients decreased by more than 50 % between simulation results at 10 km resolution and 1 km resolution. When multiple downstream connectivity (MDC) is represented, simulation results slightly improve with finer spatial resolution. The SDC simulations result in excessive backflows on very flat floodplains due to the restrictive flow directions at finer resolutions. MDC channels attenuated these effects by maintaining flow connectivity and flow capacity between floodplains in varying spatial resolutions. While a regional-scale flood was chosen as a test case, these findings should be universal and may have significant impacts on large-to globalscale simulations, especially in regions where mega deltas exist.These results demonstrate that a GRM can be used for higher resolution simulations of large-scale floods, provided that MDC in rivers and floodplains is adequately represented in the model structure.

Toward continental hydrologic–hydrodynamic modeling in South America

“…Regarding river dynamics, flows in the Amazon are largely affected by floodplains over extensive flat terrains, causing significant flood peak delay and attenuation (Richey et al, 1989;Alsdorf et al, 2007;Yamazaki et al, 2011;. Because flood waves have travel times in the order of a few months, sometimes out of phase because of the seasonal differences in precipitation (Richey et al, 1989), rivers are subject to strong backwater effects that extend for several hundred kilometers upstream of the river mouth or the confluence of its tributaries (Meade et al, 1991;Getirana and Paiva, 2013;Paiva et al, 2013), existing in both highand low-water periods (Trigg et al, 2009). To the north, the Orinoco basin shares some characteristics of the Amazon, such as a unimodal flood pulse and low interannual variability of floodplain inundation, especially in the Llanos region (Hamilton et al, 2002).…”

A first collective validation of global fluvial flood models for major floods in Nigeria and Mozambique

“…At present, there is currently no well-developed method to represent channel bifurcation in 1D fluvial models. A better representation of bifurcation would improve the performance of both 1D and 2D sub-grid models in areas of high bifurcation, such as floodplains [48].…”

Toward continental hydrologic–hydrodynamic modeling in South America

“…La Plata basin , which can ultimately impact model results. Model resolution and the ability to route discharge in downstream multi-directions (e.g., rivers with bifurcations and anabranching networks) can affect simulated water levels and flooded areas (e.g., Mateo et al, 2017), which has been taken into account in recent studies with MGB (e.g., Pontes et al, 2017;Fleischmann et al, 2018) but not in this continental model application. Other model assumptions like an approximation of rectangular channels and ineffective flow over floodplains may also affect the results.…”