Climate Controls on Runoff and Low Flows in Mountain Catchments of Western North America

In the mountainous regions of western North America, snowmelt recharges groundwater and provides ecosystem‐sustaining base flow during low‐flow periods. Continued warming is expected to have large impacts on snowmelt hydrology and on low‐flow regimes, but the relative impact of temperature and precipitation on low flows is unclear. To address this knowledge gap, the dominant climate controls on summer and winter season low flows in 63 near‐natural catchments in mountainous ecoregions of western North America are identified with correlation analysis, and low‐flow sensitivity to temperature and precipitation is quantified with multiple linear regression analysis. Results show that precipitation is the dominant control on the interannual variability of annual runoff and on the duration and severity of summer and winter low flows. The temperature sensitivity of low flows, however, can be as much as twice that of annual runoff. Warm winters correspond to significantly lower runoff; significantly longer, more severe summer low flows; and significantly shorter winter low flows. This highlights the importance of winter climate conditions for runoff and low flows in these mountain catchments and provides another line of evidence regarding the impacts of climate change on snowmelt hydrology.