Evapotranspiration-Soil Moisture Coupling Relationships from the Field to Satellite Scale

Evapotranspiration (ET) and soil moisture (SM) are key processes controlling land-atmosphere interactions. ET and SM determine water, carbon, energy, and biogeochemical cycles. ET and SM are coupled with SM limiting ET in water-limited regions, resulting in a broad definition of energy and water-limited regimes around the globe. ET-SM coupling relationships are key to understanding feedbacks between the land surface and atmosphere, and also give an estimate of the land-atmosphere coupling strength. Current ET-SM coupling relationships are modeled with ET as a piece-wise linear function of soil moisture. A linear ET-SM coupling relationship is assumed in the water-limited regime while ET is assumed decoupled from SM (and dependent on energy) in the energy-limited regime. However, the piece-wise linear ET-SM coupling relationships were developed at the point scale and might vary at the field to regional scales. Here we explore the ET-SM coupling relationships and SM limiting thresholds for ET from the field to regional scale. We also investigate the effect of weather variables, seasonality, and land cover types on ET-SM coupling strength. Eddy covariance and soil moisture monitoring systems were used to estimate ET and SM, respectively, at nine sites in Texas. These field measurements were used together with LANDSAT and SMAP remote sensing satellite estimates of ET and SM, respectively. This analysis allows exploration of both the spatial and temporal variations of the ET-SM coupling relationships.