Influence of river network representation on discharge and flooding in kilometre-scale CaMa-Flood simulations across Australia

Australian catchments exhibit diverse hydrological responses across climates, ranging from humid tropical and temperate systems to arid regions with intermittent rivers. Accurately representing this diversity requires river routing models that resolve drainage connectivity, floodplain storage and travel times at high spatial resolution. In this study, we present a novel approach using an Australia wide CaMa-Flood configuration at ~1.5 km (1 arc-minute) resolution, using MERIT-Hydro and Australian Geofabric DEMs to parameterize drainage networks and river geometry

The routing system is driven by projected runoff from the Bureau of Meteorology's operational Australian Water Resources Assessment (AWRA) model, enabling multi-decadal simulations of river discharge and floodplain dynamics across contrasting hydro-climatic regimes. To allow investigating effects of hydrography-driven differences in discharge, water level and inundation, we perform paired CaMa-Flood simulations using identical AWRA runoff. We compare (i) a river network derived from the MERIT digital elevation model and (ii) the Australian Geofabric river network and attributes.

We investigate a range of river systems including low-gradient floodplains, endorheic basins and ephemeral river systems, where flow intermittency and channel–floodplain interactions strongly control downstream hydrological behaviour. Modelled discharge and water levels are evaluated against in situ streamflow and stage gauge observations, while simulated flood extents are compared with satellite-based inundation maps derived from ICEYE synthetic aperture radar imagery. Model behaviour is analysed across representative catchments spanning tropical monsoonal, temperate, semi-arid and arid climates to identify scale-dependent controls on hydrological response. We further assess numerical stability and computational performance to quantify the feasibility of kilometre-scale routing for large-domain and ensemble applications. 

Our results demonstrate that high-resolution routing substantially improves representation of river connectivity and flood dynamics, particularly in dryland environments, providing a robust framework for catchment-scale hydrological analysis and climate-impact studies including future flood-risk assessment and across diverse Australian environments. Future developments will extend this framework through coupling with ocean circulation models to assess the combined influence of tides and storm surge on coastal flood hazard, enabling the evaluation of compound river-coastal flooding processes.