Quantifying contributions of snow to surface water supply in the western U.S.

Daniel Raynor, Seshadri Rajagopal, Kelley Sterle

ABSTRACT
Cities in the western U.S. are typically located at the foothills of mountains and derive significant portions of their water supply from snow-fed rivers and groundwater. Recent studies indicate that snow accumulation and melt is changing across the West due to climate, altering both the availability of surface water supplies and the recharge of groundwater. Demand for water in these cities continues to rise as increased population and economic growth put greater demands on surface and groundwater supplies. Therefore, adapting to changes in snow water availability poses great challenges for cities. Understanding the degree to which western cities are impacted requires us to first quantify the fraction of their water supply derived from snow using physical metrics of watershed snow hydrology. We identify 12 cities in the western U.S. with a total population of over 8 million people and the headwater basins associated with their water supply. Using climatological data from PRISM High-Resolution Spatial Climate Data (PRISM) and the North American Land Data Assimilation Systems (NLDAS), we quantify: (1) the contribution of annual precipitation that falls as snow; and (2) the contribution of snowmelt to annual surface water runoff. A comparison across the 12 cities suggests that San Francisco derives the most (74%) of their water supply from snow among the selected cities, whereas Portland derives the least (~0%). Analysis from the two datasets yielded similar results, suggesting a defensible and accurate methodology for estimating the contribution of snow to western U.S. cities’ water supply. Future work will explore additional dimensions of climate-induced changes to water supply, including the water use communities and supplementary water supply in each of these watersheds.

Keywords: water supply, snowpack, snowmelt, climate change
Citation: Raynor, D., et al., 2018, Quantifying Contributions of Snow to Surface Water Supply in The Western U.S.. Journal of the Nevada Water Resources Association, Winter 2018, p. 5-17.
DOI: 10.22542/jnwra/2018/1/1. Copyright 2018 Nevada Water Resources Association