Aspects of boreal forest hydrology: from stand to watershed

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Aspects of boreal forest hydrology: from stand to watershed

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Title: Aspects of boreal forest hydrology: from stand to watershed
Author: Nijssen, Bart
Abstract: This dissertation evaluates land surface hydrologic processes in the boreal forest using observations collected as part of the Boreal Ecosystem Atmosphere Study (BOREAS). Three separate studies, two of which have appeared as journal publications, and one of which has been submitted for publication, are included. The first study describes the application of a spatially-distributed hydrologic model, originally developed for mid-latitude forested environments, to selected BOREAS flux measurement sites. Compared to point observations at the flux towers, the model represented energy and moisture fluxes reasonably well, but shortcomings were identified in the soil thermal submodel and the partitioning of evapotranspiration into canopy and sub-canopy components. As a first step towards improving this partitioning, a new parameterization for transmission of shortwave radiation through boreal forest canopies was developed in the second study. The new model accounts for the transmission of diffuse and direct shortwave radiation, multiple scattering in the canopy, and multiple reflections between the canopy layers. Simulated sub-canopy radiation compared well with observations at a mature jack pine site, but errors were larger at a mature black spruce site. Absolute model errors were small in all cases compared to above-canopy radiation. The final study evaluates the origin of apparent water balance anomalies in the White Gull Creek Basin in the BOREAS southern study area during the 1994--1996 period, with particular emphasis on the fate of precipitation that occurred during an unusually wet period during July, 1994. Although precipitation was balanced by evapotranspiration and runoff in 1995 and 1996, it exceeded the sum of the latter two terms by 89 mm in 1994. Because field observations did not suggest increased storage at the end of the 1994 growing season, it seems likely that most of the excess precipitation evaporated when the basin was extremely wet after the heavy precipitation in July 1994. This suggests that the evaporative fluxes measured at the BOREAS flux towers under-represented the flux from the larger area during periods when the basin was very wet.
Description: Thesis (Ph. D.)--University of Washington, 2000

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