In the Pacific Northwest (PNW), concern about the impacts of climate and land
cover change on water resources, flood-generating processes, and ecosystem dynamics
emphasize the need for a mechanistic understanding of the interactions between forest
canopies and hydrological processes. A detailed measurement and modeling program
during the 1999 and 2000 hydrologic years characterized hydrological conditions and
processes in a 500-600 year old Douglas fir-western hemlock seasonal temperate
rainforest. The measurement program included sub-canopy arrays of radiometers,
tipping bucket rain gauges, and soil temperature and moisture probes, to supplement a
vertical temperature and humidity profile within the forest canopy. Analysis of the
precipitation interception characteristics of the canopy indicated that the mean direct
throughfall proportion was 0.36, and the mean saturation storage was 3.3 mm.
Evaporation from small storms insufficient to saturate the canopy comprised 19% of
the net interception loss, and canopy drying and evaporation during rainfall accounted
for 47% and 33% of the net loss, respectively. Results of the measurement program
were used to modify the Simultaneous Heat and Water (SHAW) model for forested
systems. Changes to the model include improved representation of interception
dynamics, stomatal conductance, and within-canopy energy transfer processes. The
model effectively simulated canopy air and vapor density profiles, snowcover
processes, throughfall, soil water content profiles, shallow soil temperatures, and
transpiration fluxes for both a calibration period and for an uncalibrated year. 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 evapotranspiration decreased from a maximum monthly mean of 2.17 mm
day����� in July to 1.34 mm day����� in September, as a result of declining soil moisture and
net radiation. Our results indicate that a relatively simple parameterization of the
SHAW model for the vegetation canopy can accurately simulate seasonal hydrologic
fluxes in this environment. Application and validation of the model in other forest
systems will establish similarities and differences in the interactions of vegetation and
hydrology, and assess the sensitivity of other systems to natural and anthropogenic
perturbations. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32557 |
| Date | 02 October 2001 |
| Creators | Link, Timothy E. |
| Contributors | Unsworth, Michael H., Marks, Danny |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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