Reply on AC1

Abstract

The quest for hydrological hyper-resolution modelling is already on-going for more than a decade. While global hydrological models (GHMs) have seen a reduction in grid size, thus far they never have been consistently applied at hyper-resolution (<= 1km) at the large scale. Here, we present the first application of the GHM PCR-GLOBWB at 1 km over Europe. We thoroughly evaluated simulated discharge, evaporation, soil moisture, and terrestrial water storage anomalies, and subsequently compared results with the ‘established’ 10 km and 50 km resolutions of PCR-GLOBWB. Subsequently, we could assess the added value of this first hyper-resolution version of PCR-GLOBWB as well as understand model and data requirements for future improvements. We found that for most variables epistemic uncertainty is still large. Merely for simulated discharge we can confidently state that model output at hyper-resolution improves over coarser resolutions. This first large-scale hyper-resolution modelling attempt shows that applying a GHM consistently is by now feasible with improved data availability and computer power. Also, simulated discharge improves due to better representation of the river network at 1 km. However, currently available observations are not yet widely available at hyper-resolution or lack sufficiently long timeseries, which makes it difficult to assess the performance of the model for other variables at hyper resolution. At the model side, hyper-resolution applications require improved parameterization and implementation of physical processes to be able to resemble the dynamics and spatial heterogeneity at 1 km. With this first application of PCR-GLOBWB at 1 km, we contribute to meeting the ‘grand challenge’ of hyper-resolution modelling. As such, it should be seen as a modest milestone on a longer journey towards locally relevant model output which requires a community effort from both model developers and data providers.