FLUVIAL-EB: Developing a spectral physically-based energy balance model to predict river temperatures

Abstract:

River temperatures are controlled by climate, flow of the water, and the absorption of shortwave radiation which is controlled by the wavelength-dependent properties of the water and the river bed. We developed a physically-based numerical river energy balance model in order to understand the impacts of changes to river temperatures under current and future climates. The Fluvial Energy Balance Model (FLUVIAL-EB) integrates a full spectrum solar radiation balance model with turbulent heat fluxes using bulk aerodynamic methods, bed conduction, advection, diffusion, and a 1D hydraulic model over the length of a river to predict the energy balance and changes in river temperature. The model represents key radiative heat transfer processes including reflection and absorption of light at all wavelengths at the water surface, water column, and the bed. We used FLUVIAL-EB together with meteorological data and data derived from regional climate models to predict river temperatures along the length of the San Joaquin River in the California Central Valley. Results show that variations in sediment albedo ranging from gravel to sand, common in lowland rivers downstream of dams, can influence river temperatures across a reasonable range of river discharges. Ongoing work evaluates the impacts of historical or projected climate variability and change on the energy balance and river temperature.