Hydrological model intercomparison in cold regions: challenges, insights, and future paths – a case from Nelson-MIP II

Intercomparison studies have evaluated the utility and constraints of existing hydrological and climate models worldwide. While some of these hydrological studies focused on cold Northern latitude regions, the initial phase of the Nelson Churchill River Basin (NCRB) Model Intercomparison Project (Nelson-MIP) was the sole effort to examine unregulated watersheds in this transboundary basin in Southwestern Canada and Northwestern United States. Thus far, there remains a lack of clarity regarding the performance of various models in regulated watersheds around the globe and specifically within this complex region. Therefore, the primary aim of this study, constituting the second phase of the Nelson-MIP project, is to assess the performance of hydrological models in both regulated and unregulated watersheds within the NCRB, an area characterized by 95 reservoirs and managed lakes, numerous diversions and irrigation withdrawals, and significant areas of the North American Prairie region with millions of unmanaged lake and wetland systems. Four hydrological models contribute to this phase and are setup using standardized input datasets to facilitate accurate comparisons. The performance of the models is evaluated against streamflow, actual evapotranspiration (AET), and snow water equivalent (SWE) simulations. Results reveal that two models exhibit diminished streamflow performance across the Prairie region in comparison to the broader NCRB. While AET and SWE simulations were generally accurate across the entire NCRB, one model encounters challenges in replicating AET patterns across the Prairies, a factor not reflected in the streamflow evaluation. This investigation highlights structural limitations within the participating models, particularly their insufficient representation of flow regulation and contributing area dynamics, which underscores the need for future enhancements. Moreover, this study underscores the complexities involved in conducting large-scale intercomparison studies and offers strategies for addressing these challenges in future research endeavors.