Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2004
Publication Date: 6/20/2004
Citation: Link, Timothy E., Flerchinger, Gerald N., Unsworth, Mike, Marks, Danny. 2004. Simulation of water and energy fluxes in an old-growth seasonal temperate rain forest using the simultaneous heat and water (SHAW) model, abstract, American Meteorological Society, p.443-457. Interpretive Summary: In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasize the need for understanding the interactions between forest canopies, snowmelt and plant water use. Detailed measurements and model simulations were conducted on an old growth forest at the Wind River Canopy Crane Research Facility located in southwestern Washington. Our results indicate that a relatively simple representation of the vegetation canopy can accurately simulate seasonal hydrologic fluxes in this environment, except during periods of discontinuous snowcover. This will allow us to investigate how snowmelt, plant water use, and water availability might be expected to change in this system as a result of climatic shifts.
Technical Abstract: In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasize the need for a mechanistic understanding of the interactions between forest canopies and hydrologic processes. Detailed measurements during the 1999 and 2000 hydrologic years were used to modify the Simultaneous Heat and Water (SHAW) Model for application in forested systems. Major changes to the model include improved representation of rainfall interception and stomatal conductance dynamics. The model was developed for the 1999 hydrologic year and tested for the 2000 hydrologic year without modification of the site parameters. The model effectively simulated throughfall, soil water content profiles, and shallow soil temperatures for both years. The largest discrepancies between soil moisture and temperature were observed during periods of discontinuous snowcover, due to spatial variability that was not explicitly simulated by the model. Soil warming at bare locations was delayed until most of the snowcover ablated due to the large heat sink associated with the residual snow patches. During the summer, simulated transpiration decreased from a maximum monthly mean of 2.2 mm day-1 in July to 1.3 mm day-1 in September as a result of decreasing soil moisture and declining net radiation. Our results indicate that a relatively simple representation of the vegetation canopy can accurately simulate seasonal hydrologic fluxes in this environment, except during periods of discontinuous snowcover.