Soil Moisture Profiles of Ecosystem Water Use Revealed With ECOSTRESS

While remote sensing has provided extensive insights into the global terrestrial water, carbon, and energy cycles, space-based retrievals remain limited in observing the belowground influence of the full soil moisture (SM) profile on ecosystem function. We show that this gap can be addressed when coupling 70 m resolution ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station retrievals of land surface temperature (LST) with in-situ SM profile measurements. These data sets together reveal that ecosystem water use decreases with depth with 93% of sites showing significant LST coupling with SM shallower than 20 cm while 34% of sites have interactions with SM deeper than 50 cm. Furthermore, the median depth of peak ecosystem water use is estimated to be 10 cm, though forests have more common peak interactions with deeper soil layers (50-100 cm) in 37% of cases. High spatial resolution remote sensing coupled with field-level data can thus elucidate the role of belowground processes on land surface behavior. Belowground processes, like how roots use soil water for transpiration and how soil water is used for soil evaporation, remain as large uncertainties in the Earth system. This is because these belowground processes are difficult to widely observe and thus tend to only be studied at sparsely located field sites. We address these limitations here by simultaneously using high resolution (70 m scale) remote sensing measurements of land surface temperature (LST), which integrates ecosystem soil and vegetation behavior and water use, and ground networks of soil moisture (SM) measurements between 5 and 100 cm. We find that the relationship between LST and SM at different soil depths shows how ecosystems use moisture across the soil profile. Across vegetation types, our analysis suggests most water use originates from upper soil layers where soil evaporation occurs and where roots presumably preferentially draw water under nominal climatic conditions. Grassland sites tend to have a greater preference for use of moisture in upper soil layers than for forested sites, which show an increase in deeper water use below 50 cm. We therefore demonstrate that such methods can reveal how ecosystems respond to SM across the rootzone and across a range of globally available sites. High resolution satellite retrievals of land surface temperature can reveal ecosystem water use when coupled with soil moisture (SM) networks Across vegetation types, evaporation tends to mainly use water from the upper soil layers with a decrease of SM use with depth Grassland sites tend to have more frequent ecosystem water use of upper layer SM than forested sites