Dr. Daniel Cayan, Research Meteorologist at the Scripps Institution of Oceanography at UC San Diego will present, “Diminishing Odds of ‘Normal’ Spring Snowpack In California’s Mountains“.

Summary:
A substantial fraction of California’s water supply derives from spring and early summer mountain snowmelt, but this contribution varies considerably.   From year to year over the historical record, the spring snow water content in California has varied by a factor of nearly 10.  This variation has been due mostly to interannual precipitation fluctuations, although as underscored by the recent warm drought in California, temperature has played an additional role.  In the future, the mix of precipitation and temperature influences is projected to shift.  As climate warms under increasing atmospheric greenhouse gas concentrations, the spring and early summer snowpack in the Sierra Nevada and other snow-dominated watersheds will decline substantially.  Here we explore effects of projected climate changes on the odds of various snow pack using an ensemble of downscaled climate-change projections under two greenhouse gas emissions scenarios. Using VIC hydrological model simulations of the snow accumulation aggregated over California, we investigate: a) changing odds of obtaining spring snow-water volumes that meet or exceed the historical median and b) changing odds that spring snow pack is very small in any given year.   Notably, the simulated dependence of California-wide spring snow water content on seasonal temperature change is nearly linear over most of the range of changes represented in the ensemble, and a rule of thumb that emerges is that California loses about 17% of present-day spring snow pack for each 1°C of warming.

Biography:
Dr. Dan Cayan is a climate researcher at the Scripps Institution of Oceanography, UC San Diego.

Cayan’s work is aimed at understanding climate variability and changes over the Pacific Ocean and North America and how they affect the water cycle and related sectors over western North America. He has specific interests in regional climate in California and has played a leading role in a series of California climate vulnerability and adaptation assessments.  He is also

Involved with programs to deliver improved climate information to decision makers: the California Nevada Applications Program (CNAP), sponsored by the NOAA RISA Program and the Southwest Climate Science Center, sponsored by the US Geological Survey, Department of Interior.