The Warming of Lake Tahoe

Abstract

We investigated the effects of climate variability on the thermal structure of Lake Tahoe, California-Nevada, 1970, and with principal components analysis and step-wise multiple regression, related the volume-weighed average lake temperature to trends in climate. We then used a 1-dimensional hydrodynamic model to show that the observed trends in the climatic forcing variables can reasonably explain the observed changes in the lake. Between 1970 and 2002, the volume-weighted mean temperature of the lake increased at an average rate of 0.015 • C yr −1 . Trends in the climatic drivers include 1) upward trends in maximum and minimum daily air temperature at Tahoe City; and 2) a slight upward trend in downward long-wave radiation. Changes in the thermal structure of the lake include 1) a long-term warming trend, with the highest rates near the surface and at 400 m; 2) an increase in the resistance of the lake to mixing and stratification, as measured by the Schmidt Stability and Birge Work; 3) a trend toward decreasing depth of the October thermocline. The long-term changes in the thermal structure of Lake Tahoe may interact with and exacerbate the well-documented trends in the lake's clarity and primary productivity.

Climate change in the Tahoe basin: regional trends, impacts and drivers

“…2.3 Lake temperature and thermal structure Previous calculations of average temperature of Lake Tahoe ran from December, 1969 to October 2002 (Coats et al 2006). Using an identical methodology the record for the Lake was updated through August 2007.…”

“…Since the average temperature of Lake Tahoe was last calculated through 2002 (Coats et al 2006), the lake's annual minimum temperature has continued to increase, reaching its highest level ever in late February-early March, 2007. The annual maximum temperature, however, has not increased over the same period.…”

“…Due to concerns about progressive eutrophication and loss of clarity, the lake has been studied intensively since the mid- 1960s, and has been the focus of major efforts to halt the trends in clarity and trophic status. Previous work on the effects of climate change on the lake (Coats et al 2006) has shown (1) that the lake is warming at an average rate of about 0.015 • C year −1 ; (2) the warming trend in the lake is driven primarily by increasing air temperature, and secondarily by increased downward long-wave radiation; (3) the warming trend on monthly and annual time scales is correlated with the Pacific decadal oscillation (PDO) and (to a lesser extent) with El Niño-southern oscillation (ENSO); (4) the warming of the lake is modifying its thermal structure, and increasing its resistance to deep mixing. Recent work on climate change impacts in the western USA has focused attention on the shift in snowmelt timing toward earlier dates (Aguado et al 1992;Dettinger et al 2004;Cayan et al 2001;Dettinger and Cayan 1995;Johnson et al 1999;Stewart et al 2005), the shift from snow to rain (Knowles et al 2006;Regonda et al 2005), the earlier onset of spring (Cayan et al 2001); and the effect that these changes will have on water supply in California and throughout the western USA Barnett et al 2008;Mote et al 2005).…”

Effects of climate change on thermal properties of lakes and reservoirs, and possible implications

“…However, due to progressive loss of clarity, at the rate of 0.22 m/year (Tahoe Environmental Research Center (TERC) 2008), the lake has been the focus of major efforts by local, state, and federal agencies and policy-makers to halt the trend in clarity and trophic status. Moreover, records of the past 38 years show that Lake Tahoe has become both warmer and more stable (Coats et al 2006;Coats 2008). Air temperature and precipitation, and their hydrologic linkages (e.g.…”

20th Century Atmospheric Deposition and Acidification Trends in Lakes of the Sierra Nevada, California, USA

“…6−8 At the same time, climate change is altering hydrologic and water temperature regimes, which may further contribute to variability in productivity and algal community shifts. 9,10 The Clean Air Act and Amendments (CAAA) is the primary policy for improving air quality and reducing atmospheric deposition in the United States (US). The legislation targets decreases in acid deposition and the recovery of surface waters from acidification and prohibits deterioration of air quality in national parks and wilderness areas, where a large proportion of western mountain lakes occur.…”