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"The results show that, hydrologically, the most important vegetation-related change has been a general tendency towards decreased vegetation maturity in the forested areas of the basin."

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Hydrological Processes
Volume 14, Issue 5 , Pages 867 - 885
Published Online: 21 Mar 2000
Copyright (c) 2000 John Wiley & Sons, Ltd.

Effects of land cover change on streamflow in the interior Columbia River Basin (USA and Canada)

Bernt Matheussen, Robin L. Kirschbaum, Iris A. Goodman, Greg M. O'Donnell, Dennis P. Lettenmaier

Funded by:
Office of Research and Development, US Environmental Protection
Agency; Grant Number: DW 12937588-01-0

Keywords
vegetation change; streamflow; evapotranspiration; snow processes

Abstract
An analysis of the hydrological effects of vegetation changes in the
Columbia River basin over the last century was performed using two
land cover scenarios. The first was a reconstruction of historical
land cover vegetation, c. 1900, as estimated by the federal Interior
Columbia Basin Ecosystem Management Project (ICBEMP). The second was
current land cover as estimated from remote sensing data for 1990.
Simulations were performed using the variable infiltration capacity
(VIC) hydrological model, applied at one-quarter degree spatial
resolution (approximately 500 km2 grid cell area) using
hydrometeorological data for a 10 year period starting in 1979, and
the 1900 and current vegetation scenarios. The model represents
surface hydrological fluxes and state variables, including snow
accumulation and ablation, evapotranspiration, soil moisture and
runoff production. Simulated daily hydrographs of naturalized
streamflow (reservoir effects removed) were aggregated to monthly
totals and compared for nine selected sub-basins. The results show
that, hydrologically, the most important vegetation-related change
has been a general tendency towards decreased vegetation maturity in
the forested areas of the basin. This general trend represents a
balance between the effects of logging and fire suppression. In those
areas where forest maturity has been reduced as a result of logging,
wintertime maximum snow accumulations, and hence snow available for
runoff during the spring melt season, have tended to increase, and
evapotranspiration has decreased. The reverse has occurred in areas
where fire suppression has tended to increase vegetation maturity,
although the logging effect appears to dominate for most of the
sub-basins evaluated. Predicted streamflow changes were largest in
the Mica and Corralin sub-basins in the northern and eastern
headwaters region; in the Priest Rapids sub-basin, which drains the
east slopes of the Cascade Mountains; and in the Ice Harbor
sub-basin, which receives flows primarily from the Salmon and
Clearwater Rivers of Idaho and western Montana. For these sub-basins,
annual average increases in runoff ranged from 4·2 to 10·7% and
decreases in evapotranspiration ranged from 3·1 to 12·1%. In
comparison with previous studies of individual, smaller sized
watersheds, the modelling approach used in this study provides
predictions of hydrological fluxes that are spatially continuous
throughout the interior Columbia River basin. It thus provides a
broad-scale framework for assessing the vulnerability of watersheds
to altered streamflow regimes attributable to changes in land cover
that occur over large geographical areas and long time-frames.
Copyright (c) 2000 John Wiley & Sons, Ltd.
Received: 5 November 1998; Accepted: 2 July 1999