Climate and Streamflow Trends in the Columbia River Basin: Evidence for Ecological and Engineering Resilience to Climate Change

Large river basins transfer the water signal from the atmosphere to the ocean. Climate change is widely expected to alter streamflow and potentially disrupt water management systems. We tested the ecological resilience-capacity of headwater ecosystems to sustain streamflow under climate change-and the engineering resilience-capacity of dam and reservoir management to overprint a climate change signal-in seven sub-basins of the Columbia River from 1950 to 2011. Sub-basins had a headwater gauge above dams with a long-term streamflow record and a nearby climate station with a long-term record of air temperature and precipitation, as well as matching long-term streamflow records at gauges downstream of dams. Trends were fitted to daily data for maximum and minimum temperature, precipitation, and streamflow over the period of record (mostly 1950-2011). Consistent with predicted streamflow response to climate warming, annual snowmelt runoff peaks in five of seven headwater basins shifted to a few days earlier over the period 1950 to 2010, but the changes were small, displaying ecological resilience. Below dams, streamflow change was attributable to reservoir operation for flood control (reduced annual peak flows) and irrigation (augmented late summer low flows), as well as flow management for hydropower, navigation, and recreation, but predicted streamflow responses to climate change were absent, indicating engineering resilience. Thus, to date, climate-warming effects on streamflow have been limited to headwaters, and flow regulation has obscured the expression of climate change on streamflow below dams in the Columbia River basin.