Improvements of the land surface configuration to better simulate seasonal snow cover in the European Alps with the CNRM-AROME (cycle 46) convection-permitting regional climate model

Abstract. Snow cover modeling remains a major challenge in climate and numerical weather prediction (NWP) models, even in recent versions of high-resolution coupled surface-atmosphere (i.e. at km-scale) regional models. Evaluation of recent climate simulations, carried out as part of WCRP-CORDEX Flagship Pilot Study on Convection with the CNRM-AROME convection permitting regional climate model at 2.5 km horizontal resolution, has highlighted significant snow cover biases, severely limiting its potential in mountain regions. These biases, which are also found for AROME NWP model results, have multiple causes, involving atmospheric processes and their influence on input data to the land surface models, in addition to deficiencies of the land surface model itself. Here we present improved configurations of the SURFEX-ISBA land surface model used in CNRM-AROME. We thoroughly evaluated these configurations on their ability to represent seasonal snow cover across the European Alps. Our evaluation was based on coupled simulations spanning the winters of 2018–2019 and 2019–2020, which were compared against remote sensing data and in situ observations. Specifically, the study tests the influence of various changes to the land surface configuration, such as using a multi-layer soil and snow scheme, multiple patches for land surface grid cells, new physiographic databases, and parameter adjustments. Our findings indicate that using more physically detailed individual components in the surface model using only one patch did not improve the representation of snow cover due to limitations in the approach used to account for partial snow cover within a grid cell. To address these limitations, we evaluated further configurations using three patches and improved representations of the interactions between fractional snow cover and vegetation. At the end, we introduce a land surface configuration that substantially improved the representation of seasonal snow cover in the European Alps. This holds promising potential for the use of such model configurations in climate simulations and numerical weather prediction, including AROME and other high-resolution climate models.