Dr. Alex Hall: Projections of climate change in California's Sierra Nevada

Projections of climate change in 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. In a separate study, we 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. 



Dr. Hall's research is focused on reducing climate change uncertainty at both regional and global scales. At the global scale, his goal is to reduce uncertainty surrounding processes determining the climate system’s response to increases in greenhouse gases. At the regional scale, he has been active in the development of downscaling techniques to reduce uncertainty about processes that are crucial to regional climate change, but are unrepresented in global climate models. At UCLA, Dr. Hall teaches climate-related courses at the undergraduate and graduate levels, and recently launched a new major in Climate Science. Recently, he received the American Geophysical Union Atmospheric Sciences Ascent Award (2016).  Dr. Hall was a Contributing Author to the 2007 IPCC 4th Scientific Assessment of Climate Change Working Group I report, and Lead Author for Chapter 14 of the Working Group I component of the IPCC 5th Assessment Report. Dr. Hall was also selected by the State of California to be Coordinating Lead Author of the Los Angeles regional chapter of the State’s forthcoming 4th Assessment of Climate Change. At UCLA, he is the faculty director of the UCLA Center for Climate Science.

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