The “Double Whammy” of Climate Change for California’s Sierra Nevada

In this talk I will present an overview of recent research from the UCLA Center for Climate Science on climate change in the Sierra Nevada. The methodological basis of our work is a downscaling technique we call hybrid downscaling, which combines dynamical and statistical downscaling methodologies. We find that snow albedo feedback adds critical spatial structure to the future warming patterns in the region, with important follow-on effects on snowpack, runoff timing, and soil moisture. Under a “business-as-usual” scenario of greenhouse gas emission increases, springtime snowpack is reduced by about 2/3 by the end of the 21st century, runoff timing advances by roughly two months, and summertime soil moisture declines by as much as 40%. The changes are most pronounced at mid elevations, where snow albedo feedback is strongest. Under a reduced emissions scenario along the lines of the Paris Climate Agreement, the end-century changes are roughly half as large. We also examined changes in extreme precipitation in the region, finding that droughts and extremely wet years both increase significantly in frequency. Taken together, our results paint a portrait of a dramatically changed landscape by century’s end, if global greenhouse gas emissions are not reduced very soon.

Speaker: Alex Hall, UC Los Angeles