Gedalof, Peterson, and Nathan J. Mantua, “Columbia river flow and drought since 1750.” Journal of the American Water Resource Association 40 (2004): 1579-1592.
Summary:
This study used a statistical analysis of 32 tree-ring chronologies located throughout the Columbia River Basin to create a reconstructive model of the mean total flow of the Columbia River over the last 250 years and plot the frequency and fluctuation of multi-year drought events. The purpose of this study was to look at how stream and river flow had changed over time and to gauge effect of large scale atmospheric conditions (El Nino and La Nina/ Southern Oscillation (periodic temperature variations of the southern Pacific Ocean near North America) and the Pacific Decadal Oscillation (PDO) (periodic temperature variations in the northern Pacific Ocean near North America) over time. This tree-ring reconstructive model was compared with instrumental records of flow taken at The Dalles, Oregon and to a similar tree-chronology study which showed that although the reconstructed tree-ring chronology model in this paper indicated the chronological position of severe drought events the magnitude of these events is underestimated. This disparity is explained by the author as probably due to the physical distances between sampling sites and variation in tree ring growth to drought conditions. The authors found a correlation between El Nino (less flow)/La Nina (more flow) cycles and the reconstructed mean total flow of the Columbia River. They also found a correlation between the warm PDO (less flow)/ cool PDO (more flow) cycle and the mean total flow of the river. It was also seen that these two Pacific Ocean cycles also combine in effect at times augmenting or interfering with one another.
The authors came to a number of conclusions when looking at the model they had created. The first was that multi-year drought events are probably not anomalous, but simple fluctuations within the system. They also observed that drought events have not been as severe during the 20th century as would be expected by the model. This leads to the second point that the Columbia River Basin has be altered by human action over the 20th century which has led to a instrumentally measured increase in flow at The Dalles of 3.7 percent over the period 1931-1987 due to increased runoff reducing the effect of drought conditions. The third point is that the two Pacific Ocean temperature cycles have had a variable impact over the last 250 years on the flow of the Columbia River but during the 20th century the PDO has had a stronger correlation with flow that in past centuries. The authors conclude by stating that because of the continuing impact and strain that humans have had on the Columbia Basin it could be disastrous if one of the severe periodic multi-year drought events was to occur and that the risk of such an event has been underestimated due to the milder events observed during the 20th century.
Critique:
The information put forward in this paper is compelling and well thought out. The mathematical and statistical basis of the author's analysis does introduce an uncertainty into the findings and the model they created. This uncertainty is acceptable as they were attempting to just get a sense as to the accuracy of tree-ring chronologies of the Columbia Basin and look at the overall fluctuations in the river's flow. I have no real critique of the methods used in this paper as they seem to be in order and consistent with similar studies cited and the conclusions reached by the authors matched their stated goals for their analysis.
What I find interesting and how this relates to the natural history of the Columbia Basin is that despite what we have done to the river and the changes made we do not really have any control over it. This study shows that drought events occur at a fairly specific frequency with the last one predicted to occur some time in the 1970's but this was not really the case. If the cycle is still holding up the next drought event should happen toward the end of this decade. This may or may not happen, but if it does not then perhaps through unintentional intervention we have altered the drought cycle. This would mark a real change meaning that human intervention is on par with major global climate conditions with respect to the Columbia Basin. This alters the natural history of the river by making it in part artificial and it cycles perhaps more unpredictable.
reviewed by Martin Anderson
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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