A non-explicit representation of macropores in the SVS land surface model improves streamflow simulations under frozen soil conditions

Abstract. Soil freezing is a major cold region process that influences hydrological response of northern catchments, in particular during winter rainfall and snowmelt events. Ice within the soil matrix reduces the pore space available for water to infiltrate, while the presence of soil macropores in structured soils maintains rapid water percolation even in frozen conditions. Representing the complex effect of soil freezing on water infiltration in land surface models is a challenging task. This is particularly true for operational models, where physical process integration must balance performance improvements against computational efficiency and complexity. In this study, we propose a conceptual approach to represent the effects of macropores on frozen soil infiltration into the Soil, Vegetation, and Snow (SVS) model used within the operational prediction systems of Environment and Climate Change Canada (ECCC). We assessed the effects of this new configuration (Fr-MP) on streamflow simulations at more than 580 hydrometric stations located in the Great-Lakes and Saint-Lawrence domain over a five-year period. The conceptual representation of macropores improves the Kling-Gupta Efficiency (KGE) at 88 % of the assessed stations, resulting in an increase in the median KGE of 0.28 compared to the configuration without macropores and soil freezing. Detailed analysis of a decomposed hydrograph shows that the Fr-MP configuration increases SVS soil drainage (slow response) and reduces surface runoff and lateral flow (quick response). To ensure that the proposed change is also acceptable in the context of operational numerical weather prediction, an evaluation of its impact on soil freezing depth as well as screen-level temperature and dew point temperature predictions is performed against in-situ observations. These results support the potential operational implementation of the Fr-MP configuration at ECCC for numerical weather and streamflow prediction.