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Green to grey: numerical experiments to explain multi-scale hydrologic responses to mountain pine beetle tree mortality in a headwater basin
Penn, Colin Andre Kress
Penn, Colin Andre Kress
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2014
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2014
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2014-11-01
Abstract
The scaling behavior of mountain pine beetle (MPB) induced tree mortality impacts on a headwater hydrologic system were investigated using an integrated physical modeling framework with a high-resolution computational grid. A Green Phase simulation and Grey Phase simulation with 36% impacted area, each with identical atmospheric forcing for a normal water year, were analyzed at multiple scales to examine the factors that control differences between them. Individual locations within the larger model were shown to maintain hillslope-scale processes affecting snowpack dynamics, total evapotranspiration, and soil moisture that are comparable to several field based studies and previous modeling work. At larger scales, the magnitude of MPB impacts were obscured due to compensating factors, and the role of unimpacted terrain influence was included. Increasing late-summer soil evaporation was shown to compensate for reduced transpiration in the Grey Phase, while overall snowpack dynamics were more dependent on elevation effects than MPB impacts. Annual water yield increased during Grey Phase simulations by 11%; an amount that would be difficult to assess with long-term gage observations due to inter-annual climate variability. The scaling behavior of MPB impacts show that effects on hydrology observed at the hillslope scale can be dampened when considering a larger and more dynamic system. This behavior may change under extreme conditions, e.g. increased total MPB impacted area or a water year with above average snowpack. The fine-scale resolution of this model has the ability to inform future observations and the inputs that regional-scale modeling should incorporate to better represent this dynamic system.
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