Matheussen, Bernt, Robin L. Kirschbaum, Iris A.Goodman, Greg M. O'Donnell, and David P. Lettenmaier. "Effects of Land Cover Change on Streamflow in the Interior Columbia River Basin (USA and Canada)." Hydrological Processes 14 (2000): 867-885. (reviewed by Martin Anderson)
Summary:
The purpose of this study was to look at the effect of human alteration to land cover by construction of a variable infiltration capacity (VIC) model to simulate various land use scenarios. The authors developed a computer simulation that divided the Columbia River Basin into 9 sub-basins consisting of 1119 sections of 500 square kilometers each. This model takes into account the composition of soils, evapotranspiration, ground water patterns, topography, vegetative cover (30 types), climate, weather and precipitation patterns, snow accumulation, melting patterns, elevation, energy flow, and temperature.
The model was run using two different scenarios: 1900 land cover condition (taken from settler and survey accounts) and 1990 land cover condition. The program modeled the Columbia River Basin under these conditions using the environmental conditions during the ten years between 1979 and 1989. By modeling these two experimental conditions under the same time period a means of comparison is established. It is important to note that these scenarios hold the climate stable which eliminates the effect of rising global temperature and the ocean temperature patterns in the Pacific.
The authors found that when comparing the 1990 vegetative conditions to 1900 vegetative conditions there is an increase in annual runoff in all but one of the sub-basins, Oxbow basin which sits in the semi-arid/arid area of eastern Oregon and Washington , where a small decrease was noted. This increase in runoff was accompanied by a decrease in the rate of evapotranspiration at all sites except the Oxbow sub-basin. This indicates that the moisture that had been transpired by vegetation was going in part to increase the runoff for a respective sub-basin.
The authors suggest that the situation is not as straightforward as precipitation just coursing into a stream. This situation is a function of not only a decrease in the number of trees but also the functional maturity of forests. Comparing the two vegetative conditions there is a difference in the type and maturity of vegetation that is present.
Old growth (mature) forests have almost been totally replaced with logged and replanted forests. These are the most important areas in terms of runoff for the basin due the generally high elevation of these forests and the large amount of rainfall that they usually receive. This condition leads to a decrease in the total amount of ground cover and vegetation which causes quicker runoff due to precipitation and an earlier snowmelt due to fewer trees to shade the ground. The result of this is that there is an earlier spring flow and less water later in the season.
A similar situation exists in the low lands of the basin but for most the purposes of this model the semi-arid/arid areas in eastern Oregon , Washington , and northern Nevada (most of the Oxbow sub-basin) contribute less overall water to the Columbia . It is still concerning to the authors though that there is less runoff coming from the Oxbow areas where water resources are already stretched.
Critique:
The article is well written, thought out, and provides a climate-independent look at the basin's hydrology. The authors included approximately 11 pages of charts and graphs that make their sometimes technical jargon understandable. Included in these charts are a series of color-coded maps that represent the basin as divided by the computer model. These charts show changes in runoff, evapotranspiration, and vegetation between the 1900 and 1990 vegetative conditions making the conclusion of the authors easier to see. This article would be of interest to anyone looking at the effect of human activity on the Columbia River Basin particularly de-forestation and conversion of land to agricultural uses.
This climate independent model is interesting because it provides a different point of view from the normally global warming-driven simulations in the literature. This alternate point of view serves to augment these other simulations and adds depth to the big picture of the basin. Like other simulations looking at the effect of man on the Columbia River Basin the conclusion of this article is that at some point the natural history of the basin become the history of man's activity and influence.
The article consists of 25 pages (approximately 11 pages consist of charts and graph) with 41 references.
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
Send e-mail to the Webmaster