Science Source

Declining annual streamflow distributions in the Pacific Northwest United States, 1948–2006

States that although increasing variability in annual flows has been noted, the nature of those changes is largely unexplored
Tests for trends in the distribution of annual runoff using quantile regression at 43 gages in the Pacific Northwest
Finds that 72% of the stations showed significant (a = 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
Finds that 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