Distance to River Controls Riparian Ecosystem Water Use and Stress in a Semi-arid Watershed

Abstract:

Riparian plants in dryland environments rely on subsurface water availability, which determines the spatial variability of plant water use and productivity. However, the subsurface water gradient remains hidden. Nonetheless, plant water use can uncover these unseen gradients; but, tracking plant water use at high spatial and temporal resolutions has historically been elusive. The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) now provides operational evapotranspiration data at high spatial (70 x 70 m) and temporal (1-5 days) resolutions, thus providing a new opportunity to capture the fine-scale variability of evapotranspiration over a large domain.

To analyze the spatial gradient of evapotranspiration over the Upper Columbia Priest Rapids watershed in a semi-arid climate zone, we analyzed ECOSTRESS evapotranspiration, as well as the evaporative stress index (ESI) product for natural shrublands, as a function of distance to the main stem of the river. We found a clear spatial gradient in both evapotranspiration and ESI, exhibiting an exponential decrease by moving away from the river. Also, we identified that these spatial patterns of plant water use and stress are strongly related to that of depth to groundwater table in the watershed. The results of this study provide a basis to understand the large-scale controls of groundwater on plant-water dynamics, and thus support adaptation strategies for groundwater-dependent ecosystems under changing environments.