The Southwestern United States has a greater vulnerability to climate change impacts on water security due to a reliance on snowmelt driven imported water. The State of California, which is the most populous and agriculturally productive in the United States, depends on an extensive artificial water storage and conveyance system primarily for irrigated agriculture, municipal and industrial supply and hydropower generation.

Snow accumulation is critical for water availability in the Northern Hemisphere, raising concern that global warming could have important impacts on natural and human systems in snow-dependent regions. Although regional hydrologic changes have been observed, the time of emergence of extreme changes in snow accumulation and melt remains a key unknown for assessing climate-change impacts.