Thursday, May 1, 2008
Assessing the impacts of global warming on snowpack in the Washington Cascades
The decrease in the Cascades snowpack attributable to global warming is difficult to estimate in the presence of the large year-to-year natural variability in observations of snow water equivalent. A more robust approach for inferring the impacts of global warming is to estimate temperature sensitivity ? of spring snowpack and multiply it by putative past and future temperature rises attributable to global warming.
Estimates of ? can be obtained by (a) linearly regressing year-to-year variations in observed spring snowpack upon seasonal-mean winter temperature; (b) making simple geometric considerations based on the notion that as the seasonal-mean temperature rises by the amount dT, the freezing level and the entire vertical profile of snowpack should rise by the increment dT/G , where G is the mean lapse rate; and, (c) running a hydrological model forced by daily temperature and precipitation observations. All three methods yield an estimated 20% loss of spring snowpack for a 1°C temperature rise. These estimates are consistent with the inferred accumulated snowfall derived from daily temperature and precipitation SNOTEL data, which serves as a proxy for snow water equivalent.
Considering various rates of temperature rise over the Northern Hemisphere, it is estimated that spring snow water equivalent in the Cascades portion of the Puget Sound drainage basin should have declined by 10-20% over the past 30 years due to global warming and it can be expected to decline by another 15-25% by 2050.
Joe Casola is currently pursuing a PhD in Atmospheric Sciences at the University of Washington, where he is advised by Mike Wallace. His research examines climate variability and change, especially as it relates to the Pacific Northwest. As a member of the Interdisciplinary and Policy Dimensions of the Earth Sciences (IPDES) program, Joe is also interested in how climate information is used in the management of the region's natural resources.
Prior to coming to UW, Joe received his BS in Chemistry from Duke University. He also worked as a consultant for ICF Consulting in Washington, DC, estimating greenhouse gas emissions for various Environmental Protection Agency projects, and as a math teacher at the Casablanca American School in Morocco.