INVESTIGATION OF SENTINEL-1 TIME SERIES FOR SENSITIVITY TO FERN VEGETATION IN AN EUROPEAN TEMPERATE FOREST

We evaluated Global Navigation Satellite System (GNSS) signals to monitor forest water storage, helping to close an important observational gap in plant hydraulics and micrometeorology at stand-scale. We show that signal losses in the canopy are strongly linked to three-dimensionally modeled rainfall interception. However, detecting subtle fluxes, such as internal water dynamics, dew and intercepted light rain is inhibited by signal noise, and the hydraulics properties of the ecosystem.

Vegetation water observations from 272 field-based GNSS sensors and satellite-based vegetation optical depth are compared across the western U.S. We find significant positive correlations across the sites and identify common conditions that increase the correlations including less forest cover, more homogeneous vegetation across landscapes, and large seasonal amplitudes. These field-based sensors are thus useful tools to evaluate grass and shrub water stress and validate satellite signals.

Satellite observations of Earth's land surface are important for tracking soil and vegetation water. We use data from the Soil Moisture and Ocean Salinity satellite to build a new product that cleans the raw microwave signal and yields more reliable estimates of soil moisture and vegetation water content. Tests against ground stations and other satellites show that the new record exceeds existing products and can support applications such as drought, freeze–thaw, and carbon monitoring.

This study compares established evapotranspiration products in central Europe and evaluates their multi-seasonal performance during wet and drought phases in 2017–2020 together with important soil–plant–atmosphere drivers. Results show that SEVIRI, ERA5-land, and GLEAM perform best compared to ICOS (Integrated Carbon Observation System) measurements. During moisture-limited drought years, ET (evapotranspiration) decreases due to decreasing soil moisture and increasing vapor pressure deficit, while in other years ET is mainly controlled by VPD (vapor pressure deficit).

Ecosystem resistance reflects their susceptibility during adverse conditions and can be changed by land management. We estimate ecosystem resistance to drought and temperature globally. We find a higher resistance to drought in forests compared to croplands and an evident loss of resistance to drought when primary forests are converted to secondary forests or they are harvested. Old-growth trees tend to be more resistant in some forests and crops benefit from irrigation during drought periods.