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Abstract

A catchment’s Water-input Partitioning Pattern (WPP) is defined as the relative separation of water input (i.e., rainfall and snowmelt) into storage and flowpaths (e.g., shallow flow, deep flow, ET) which ultimately control streamflow generation dynamics. This study investigates the dynamicity of catchment hydrologic function by analyzing the WPP under different natural climatic scenarios in two snow-dominated catchments. Using numerical models validated against extensive field observations, we explore how variations in snowmelt and antecedent rainfall (rainfall occurring prior to the snowmelt season) influence WPP in two catchments, Nanika and Krycklan, with contrasting physical attributes. Our results demonstrate significant monthly, seasonal, and inter-annual variations in WPP, driven by the interplay between climatic conditions, topography, and hydraulic conductivity patterns. Antecedent (Fall) rainfall before major snowmelt events as well as snowmelt dynamics are two causal drivers of the dynamicity of catchment hydrologic function (or WPP). The hydraulic conductivity pattern, both vertically and horizontally, significantly controls the catchment's WPP response to climatic variations. In Krycklan, where hydraulic conductivity is horizontally homogeneous but exponentially decays with depth, an increase in antecedent rainfall can promote shallow flowpaths. By contrast, in Nanika, with a horizontally heterogeneous hydraulic conductivity pattern, additional antecedent rainfall augments long-term subsurface storage by facilitating vertical connectivity, leading to a lesser portion of snowmelt being streamflow’s shallow and deep flowpaths. This study highlights the importance of understanding the interactions amongst climatic variations and geology to predict catchment responses to climate change, emphasizing the need for comprehensive hydrological models that account for both landscape properties and physical attributes. This research provides critical insights into the hydrologic processes governing snow-dominated catchments and underscores the complexity of predicting hydrological responses in the face of climatic variability.