The water held in soil is a critical resource for sustaining ecosystems and agriculture and, through bare-ground evaporation and transpiration through plant leaves, a primary source of surface humidity over land and driver of the land-based hydrological cycle. But despite its central importance for continental climate and hydroclimate the basic science of soil moisture, at least at regional to continental scales, is not well developed. There are several reasons for the lack of basic science understanding, among them the complexity of factors that determine soil moisture, including physical climate factors like precipitation and the surface energy available for evaporation, and biological factors that determine how much water is taken up by plant roots and transpired through leaves. The development of a basic science is also hampered by lack of observations, and by a tendency for research to focus on more applied science issues like the use of soil moisture as an input for subseasonal weather forecasting. The Principal Investigator (PI) of this CAREER award seeks to develop the basic science of soil moisture at regional to continental scales by addressing two questions: first, what are the key controls on the spatial variability of soil moisture in present-day climate? One issue here is why the latitudinal profile of continental soil moisture has a characteristic "W" shape, with a maximum at the equator and minima in the subtropics of the Northern and Southern Hemisphere