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Declining annual streamflow distributions in the Pacific Northwest United States, 1948–2006
Author(s) -
Luce C. H.,
Holden Z. A.
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl039407
Subject(s) - streamflow , snowpack , environmental science , percentile , surface runoff , climate change , water year , dryness , snow , climatology , snowmelt , precipitation , trend analysis , quantile regression , hydrology (agriculture) , physical geography , geography , drainage basin , meteorology , oceanography , geology , ecology , statistics , cartography , medicine , mathematics , surgery , geotechnical engineering , biology
Much of the discussion on climate change and water in the western United States centers on decreased snowpack and earlier spring runoff. Although increasing variability in annual flows has been noted, the nature of those changes is largely unexplored. We tested for trends in the distribution of annual runoff using quantile regression at 43 gages in the Pacific Northwest. Seventy‐two percent of the stations showed significant ( α = 0.10) declines in the 25th percentile annual flow, with half of the stations exceeding a 29% decline and a maximum decline of 47% between 1948 and 2006. Fewer stations showed statistically significant declines in either median or mean annual flow, and only five had a significant change in the 75th percentile, demonstrating that increases in variance result primarily from a trend of increasing dryness in dry years. The asymmetric trends in streamflow distributions have implications for water management and ecology well beyond those of shifted timing alone, affect both rain and snow‐dominated watersheds, and contribute to earlier timing trends in high‐elevation watersheds.