The impacts of climate change on water resources in the western United States–Paul Chan

In many regions of the world, water needed for agriculture and human consumption relies on winter mountain snowpacks. For example, the Sierra Nevada snowpack typically accounts for around 30% of California’s fresh water supply. Yet, there is evidence that climate change is decreasing seasonal mountain snowpacks globally, with potentially catastrophic consequences on water resources.

A recent article published in the scientific journal Nature shows that across the western United States (WUS), snow water equivalent declines of ~25% are expected by 2050. While WUS mountains are dependent on extreme precipitation and snowfall events to build snowpacks, they are also susceptible to changes in precipitation characteristics. The WUS water sector built its infrastructure and developed its water-resources management approach under the assumption of an abundant winter snowpack that reliably melts prior to peak water demands in summer months.

The authors of this article used climate models of different warming scenarios to project when mountain snowpack could see dramatic changes. The study shows that increasing temperatures from human-caused climate change are shrinking snowpacks and altering precipitation patterns. Under climate change condition, several key mechanisms controlling water resources will be altered. These mechanisms include rainfall, snowfall, evapotranspiration (ET), recharge of ground water, runoff, and streamflow. Even a shift from snow to rain leads to significantly lower annual streamflow.

A number of potential adaptation strategies to a low- to- no snow future need to be pursued to address both water supply availability and water demands, with, for example, hard infrastructure (including dams, canals and new supplies), management approaches, and water conservation. There are also potential approaches to increase total supply by bringing ‘new’ water into the system. These approaches can be natural or engineered approaches such as forest and vegetation management to reduce ET and increase snow storage, runoff and recharge.