Using integrated modeling to study the effect of grid resolution on hydrologic response to climate change in headwaters catchments

Management decisions are often made at the local scale but are informed by global climate models run at a much coarser resolution. At the same time, many point-scale observations are extrapolated to larger regions, where nonlinear feedbacks can exacerbate or mitigate observed changes. Scale effects are often cited to explain discrepancies between models and observations; however, few modeling studies have explicitly focused on the impact of resolution on hydrologic processes. This study leverages a hyper-resolution model of a 255km2 watershed in the Rocky Mountains to study the impact of varying grid resolution over two orders of magnitude. Given that mountain snowpack supplies water for much of the world, there have been numerous observational and modeling studies of climate change in headwater catchments. Results from these studies are often inconsistent, likely owing to feedbacks present in topographically complex regions. Modeling at different scales can help delineate uncertainty in climate change predictions, determine thresholds in feedbacks lost at coarser resolutions, and identify processes that need to be constrained by point-scale observations. This study uses integrated modeling to study the range of climate change impacts on mountainous terrain produced by different resolutions from the scale of local observations, 10m, to a regional model scale, 1km. Domain data from a hyper-resolution, fully parallelized Parflow-CLM model near Crested Butte, CO are aggregated to successively larger scales. Systematic temperature, precipitation, and land cover perturbations are applied to the 100m and 1km domains. These are compared with results from the 10m model run. This is the first study of its kind to reach 10m resolution over an entire catchment of this size. Given that this is the scale of many local observations, it provides context for an extensive literature, both in modeling and observational studies, of climate change impacts on headwater hydrology.