The Effects of Climate Change on Lake Tahoe, and Implications for Design of Best Management Practices

CLIENT:  Pacific Southwest Research Station

Lake Tahoe, renowned worldwide for its beauty, clarity, and ultra-oligotrophic status, has an ecological significance recognized in its classification as an "Outstanding National Resource Water” under the Clean Water Act. Climate change could result in a number of potential impacts to the hydrology of the Lake Tahoe Basin, including a shift in the amount and type of precipitation, stream discharge, sediment and nutrient loading characteristics, best management practice (BMP) performance, lake mixing, and water quality response.

The NHC team, working with a collection of researchers from UC Davis and other consulting firms, led two tasks within a broader Lake Tahoe Basin climate change study. Specifically, the NHC team performed: 1) statistical downscaling of precipitation projections from global climate models (GCMs) from their original roughly 2º latitude-longitude grid spacing onto a 1/8º (roughly 12 km) grid using measured data from Lake Tahoe Basin SNOTEL stations; and 2) continuous long-term BMP performance simulations under various climate change scenarios using the Pollutant Load Reduction Model.

The modeling analysis projected the percentage of precipitation falling as snow within developed areas of the Tahoe Basin would decline from an annual average of 60% to an annual average of 30%-40% by the end of the 21st century. This projected shift in precipitation patterns from snow to rain increased the frequency and magnitude of peak flows in stormwater runoff, resulting in a roughly 10% decline in treatment performance for BMPs sized to current Tahoe Basin regulatory requirements. However, at the end of the simulation period, capture and treatment of stormwater runoff remained around 80% of modeled average annual runoff. This result indicates that while performance may be reduced, current regulatory requirements in the Tahoe Basin may still provide acceptable BMP performance under the climate change scenarios analyzed.