Propagating climate and vegetation change through the hydrologic cycle in a mountain headwaters catchment.

Abstract

Prediction of hydrologic response to global climate change is paramount for regions that rely upon snowpack for their dominant water supply. Temperature increases are anticipated to be greater at higher elevations perturbing headwaters systems that provide water to millions of downstream users. In this study, the relationships between climatic change and associated vegetation succession with the corresponding response in hydrologic processes of mountainous terrain are studied in the East River headwaters catchment near Crested Butte, CO. This catchment is emblematic of other headwater systems within the upper Colorado River basin. Therefore, perturbations seen at this study site are likely to occur across the region, altering the water quantity and quality of the Colorado River. Here, we study the effect of climate-induced changes on the hydrologic response of three different characteristic components of the catchment: a steep high-energy mountain system, a medium-grade lower-energy system and a low- grade low-energy meandering floodplain. To capture the surface and subsurface heterogeneity of this headwaters system the basin has been modeled at a 10-meter resolution using ParFlow, a parallel, integrated hydrologic model. This model assesses hydrologic scenarios based on worst-case Intergovernmental Panel on Climate Change (IPCC) climate projections and an estimated worst-case scenario vegetation change observed in a warming experiment conducted in the watershed. Changes in ground evaporation, evapotranspiration (ET) snow water equivalent (SWE), and discharge are analyzed as these catchment characteristics provide useful insight into hydrologic iii response. It was found that each component responded differently depending on its inherent orographic location and geologic features. It was also found that the inclusion of vegetation change enhanced the hydrologic changes from the vegetation or warming scenarios alone. Overall, the results show decreases in discharge, shifts in the timing of peak runoff, and prolonged periods of soil moisture declines, all of which can have negative implications for water quality, quantity and vegetative productivity. iv

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