An extension of the BROOK90 hydrological model for estimation of subdaily water and energy fluxes

Abstract. We present an updated version of the BROOK90 hydrological model (B90), which integrates a closed energy and water balance on subdaily time scales. This updated version refines the time-discrete, physically based representations of soil evaporation, interception and transpiration, while also improving the simulation of snowmelt processes on vegetated surfaces. Additionally, the model includes the capability to simulate the sensible heat flux, thereby providing a comprehensive description of the energy balance in conjunction with the water balance for vegetated surfaces.

The model was validated using ICOS eddy-covariance measurements from a mature spruce forest at the Anchor Station Tharandt (DE-Tha) in Germany. The subdaily B90 model demonstrates a good agreement with observed 30-minute latent and sensible heat fluxes for dry surfaces, while its performance is less accurate for wet surfaces.

Notably, this new version of B90 does not require recalibration; parameter sets from earlier versions remain applicable. The model is well-suited for sampling intervals from 8 hours to 1 minute, depending on the availability and resolution of the input forcing data. It can be effectively used for various purposes, such as validating flux measurements, gap-filling latent and sensible heat flux data, and performing plausibility checks. However, its primary application is in the study of subdaily water balance dynamics, including processes like dew formation, interception, and fog deposition, which are typically not captured in many other daily-scaled water balance models.