Paper No. JAWRA-07-0074-P of the Journal of the American Water Resources Association (JAWRA). Discussions are open until February 1, 2009.
Relative Effects of Climate and Water Use on Base-Flow Trends in the Lower Klamath Basin1
Article first published online: 28 JUN 2008
© 2008 American Water Resources Association
JAWRA Journal of the American Water Resources Association
Volume 44, Issue 4, pages 1035–1052, August 2008
How to Cite
Van Kirk, R. W. and Naman, S. W. (2008), Relative Effects of Climate and Water Use on Base-Flow Trends in the Lower Klamath Basin. JAWRA Journal of the American Water Resources Association, 44: 1035–1052. doi: 10.1111/j.1752-1688.2008.00212.x
- Issue published online: 25 JUL 2008
- Article first published online: 28 JUN 2008
- Received June 12, 2007; accepted December 12, 2007.
- surface water hydrology;
- climate variability/change;
- Klamath River;
- permutation tests
Abstract: Since the 1940s, snow water equivalent (SWE) has decreased throughout the Pacific Northwest, while water use has increased. Climate has been proposed as the primary cause of base-flow decline in the Scott River, an important coho salmon rearing tributary in the Klamath Basin. We took a comparative-basin approach to estimating the relative contributions of climatic and non-climatic factors to this decline. We used permutation tests to compare discharge in 5 streams and 16 snow courses between “historic” (1942-1976) and “modern” (1977-2005) time periods, defined by cool and warm phases, respectively, of the Pacific Decadal Oscillation. April 1 SWE decreased significantly at most snow courses lower than 1,800 m in elevation and increased slightly at higher elevations. Correspondingly, base flow decreased significantly in the two streams with the lowest latitude-adjusted elevation and increased slightly in two higher-elevation streams. Base-flow decline in the Scott River, the only study stream heavily utilized for irrigation, was larger than that in all other streams and larger than predicted by elevation. Based on comparison with a neighboring stream draining wilderness, we estimate that 39% of the observed 10 Mm3 decline in July 1-October 22 discharge in the Scott River is explained by regional-scale climatic factors. The remainder of the decline is attributable to local factors, which include an increase in irrigation withdrawal from 48 to 103 Mm3/year since the 1950s.