| Summary: | Mountainous sub-arctic catchments typically consist of various landscape elements such as glaciers, steep topography, fractured rock outcrops and talus covered slopes, patches of permafrost, vegetated and non-vegetated shallow soils, wetlands, and lakes which are connected by surface and subsurface flows to stream networks. Hydrological flows are strongly influenced by snow and glacier melt that affects seasonal and annual runoff variability, both locally and downstream. This leads to great variability in flow to receiving hydrological systems, which makes it difficult to accurately quantify and predict water resources in downstream regions. Transport of waterborne substances such as solutes and nutrients are also extremely difficult to quantify due to this notable variability, and predictive capabilities are further hampered by still unknown effects of climate warming, which is expected to cause a change from glacial meltwater-dominated runoff to hillslope runoff. In this contribution, we present results from recent field tracer experiments along hillslopes associated with groundwater springs in the sub-arctic periglacial catchment of Tarfala, located in northern Sweden. We obtain breakthrough curves for different wet and dry antecedent moisture conditions based on seasonal variability. This is combined with rainfall-runoff recession analysis as well as physics-based numerical modelling to study and interpret the flow paths through the hillslope and its runoff-generating processes and the relative magnitudes of surface to shallow to deep subsurface runoff. Furthermore, we highlight how these model-based simulations can be used to study long-term changes of permafrost degradation and water and heat fluxes in mountainous sub-arctic catchments subject to climate change.
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