Environmental Science and Engineering Seminar

Soil moisture controls on the atmosphere play a major role in determining weather over inland continental regions, from the onset of severe storms to the temperature and humidity experienced by humans in the lower atmosphere. I will present new results from two projects related to this topic. First, results from an idealized modeling study using cloud-permitting simulations will be presented. We identify a new mechanism by which soil moisture can control precipitation: dry soils cause the atmosphere to dry out, causing more raindrops to evaporate as they fall towards the land surface, resulting in less rainfall at the surface. Second, I will present a simple theory of evaporation over land that assumes strong soil moisture controls on the temperature and humidity of the lower atmosphere. The theory drastically simplifies the estimation of evaporation, requiring no free parameters and no land surface information as inputs, even in regions where the land surface exerts a strong control on evaporation (for example, regions with low soil moisture). The theory's predictions are about as accurate as state-of-the-art eddy covariance observations. The theory can be applied to spatially and temporally widespread weather station data, opening up substantial new opportunities for studying continental evaporation.