UC Davis

Shallow soil temperature (Tss) was monitored at many clusters of sites in valley bottom areas, bordering mountain slopes, and subalpine upland areas within the Tahoe Basin of the Sierra Nevada, USA. Objectives of this survey were to: (i) accurately log Tss for an entire year across the panoply of ground surface environments that cover the southern Tahoe Basin area, and (ii) identify the primary factors responsible for inter-site variations in seasonal and annual mean Tss. The Tss data for snow-free and annual mean periods exhibit wider inter-site ranges than published observations for other regions, attributable to the great diversity of ground surface environments sampled. Two energy balance based models of ground surface temperature are introduced, each applicable to a wide variety of surface environments and formulated with regional calibration coefficients that can incorporate effects of seasonal snow-cover on annual mean Tss. The models closely fit summer monthly and annual mean Tss data from most sites, and confirm that the large inter-site range of shading (by vegetation and terrain) is responsible for most of the large inter-site range of observed Tss. Additionally, data and model results strongly suggest spatially heterogeneous soil warming rates in response to regional climate warming, and support the value of resolving spatial variations in Tss for groundwater flow tracing techniques.