The effect of vegetation type on the seasonal and diurnal cycles of soil temperature

The diurnal and seasonal cycles of soil temperature are controlled by many factors including soil thermal properties, soil water content and absorbed solar radiation at the soil surface. Absorbed solar radiation in turn depends on the albedo and shading effects provided by the vegetation canopy as well as on soil properties and snow fall. Here we focus on the effect that vegetation type has on soil temperature, using a new dataset from Kamennaya Steppe, Russia. Given the same meteorological forcing we expect to see measurable differences in the seasonal and diurnal cycles beneath different vegetation types. The data set includes measurements of soil temperature, soil moisture and freezing depth for both grassland and forest sites for the 25 year period from 1967-1991. We found that the soil beneath forests is warmer during the winter and cooler during the summer than the soil beneath adjacent grassland plots, and also that the amplitude of the diurnal cycle was lower beneath forests. The data set also contains records of the meteorological forcing variables necessary to force land surface models. Using these data we forced the Noah land surface model version 2.5.2, which does not have separate canopy energy and water budgets, and Community Land Model 3, which includes these features. We found that including an explicit vegetation canopy is important for reproducing the observed differences in diurnal and seasonal soil temperature beneath forest and grassland.