Evidence for a climate-driven hydrologic regime shift in the Canadian Columbia Basin

Abstract

Water resources from the Columbia River Basin are intensely used for domestic, agricultural, industrial and hydroelectric generation needs. Water availability in the Pacific Northwest is influenced by several ocean–atmosphere modes of climate variability that occur in the Pacific Ocean. Climate change has the potential to alter these relationships and influence both the volume and timing of streamflow in the snowmelt-dominated tributaries to the Columbia River. Here, the historical influences of climate variability and recent climate warming on the volume and timing of streamflow for 40 tributary streams in the Columbia River Basin of Canada were evaluated. Regional relationships were found between streamflow and several Pacific Ocean climate indices, including the already established relationships with the Pacific Decadal Oscillation (PDO) and El Nino/Southern Oscillation (ENSO). However, in recent decades the statistical relationship between streamflow and climate indices has become weaker, which has implications for managers using these indices as decision-making tools. A comparison of the average annual streamflow for the cool PDO phase, which occurred from 1947 to 1976, to the more recent cool phase from 1999 to 2011 indicates a 11% decline across the Canadian portion of the basin. Removing the influence of these climate indices on historical streamflow reveals decreases in the residual streamflow beginning sometime in the 1980s. The potential role of increased temperatures on streamflow was investigated, and statistically significant relationships between decreased streamflow and increased temperatures in the summer months were found, particularly with the number of days over 18°C. The results suggest that climate change may be altering the historical relationship between climate indices and streamflow in the Canadian portion of the Columbia Basin.