Is Snowpack Drought an Increasing Threat in the Pacific Northwest?

Abstract:

In spite of near normal precipitation during the winter of water year 2015, the Pacific Northwest (PNW) has experienced drought because of insufficient snow accumulation in the mountains, which was exacerbated by an unusually warm and dry summer. Low mountain snowpack resulted from an anomalously warm winter and subsequently affected water supply for irrigation, fish habitat, ecosystem, and recreation, necessitating a statewide drought emergency declaration in the Washington State. While the 2015 drought is likely a result of natural variability superposed with climate warming, we ask how the frequency of droughts of this character are likely to change as a result of anthropogenic climate change. Downscaled climate data from multiple Global Climate Models from the Fifth Climate Model Intercomparison Project were used with the Variable Infiltration Capacity (VIC) model to calculate both the Standardized Precipitation Index (SPI) and Snow Melt and Rain Index (SMRI) indices for quantifying meteorological and snowpack droughts, respectively, in the Columbia River Basin (CRB) under historic and future climate change scenarios. Our results show that snowpack droughts increase in severity and frequency in the future in response to the sensitivity of the snowpack to warming, whereas there is a less systematic trend in meteorological drought. Water resources in the CRB largely depend on the mountain snowpack and spring snowmelt. More frequent occurrence of snowpack drought will have serious implications in this system, which need to be addressed in future studies.