Understanding scale impacts of heterogeneity and topography on water and energy fluxes in mountain meadows using a fully-integrated hydrologic model

Abstract

Mountain watersheds and their subsystems are critical sources of water for much of the Western U.S. The ability to predict their behavior in response to perturbations such as climate change, grazing, mining, and pumping is becoming increasingly important. Land cover, subsurface, and topographic heterogeneity have all been shown to control infiltration rates, subsurface flow, soil moisture, and energy flux distributions. Many hydrologic models operate at scales which do not capture the variability of these parameters, often because of limited availability of computational resources and high-resolution data. The effects of these small-scale heterogeneities on local water-energy balances are thus largely unknown. This work examines the influence of small-scale heterogeneity in an alpine meadow microcatchment (250m x 300m) within the East River watershed near Crested Butte, CO, using the integrated groundwater-surface water model, ParFlow-CLM. Topography for the simulation was derived from LiDAR data taken at 0.5m resolution, and plant functional types were assigned based on remote sensing data flown for the area. A suite of ParFlow simulations were run to evaluate the impact of a systematic loss of information on integrated hydrologic response. The importance of microtopography was studied using simulations with different grid resolutions. The sensitivity of land cover was studied using homogeneous and heterogeneous representations of plant functional type and the role of subsurface heterogeneity on states and fluxes was explored using correlated, Gaussian random fields to represent the spatial distribution of soil. Output comparisons have shown that land cover heterogeneity plays an important role in controlling water and energy fluxes, such as snowmelt and ET, while topography and soil heterogeneity control water distribution within the model, as well as outflow and total storage.