OPerational moniTorIng of WAter in VEgetation(OPTI-WAVE)

Drought is an increasingly important stressor of vegetation, yet there is still no general agreement on how to model drought effects on primary production. One reason is the lack of observational data on the water status of vegetation, i.e. vegetation canopy water content (VCW). There are remote sensing methods for near-surface soil moisture, but this is only indirectly connected to root-zone water content; emerging methods for above-ground biomass; and a well-established, microwave-based measure of vegetation optical depth (VOD), which however combines signals of biomass and water content, limiting its usefulness. This project will develop a method to provide accurate global coverage of VCW from space, by exploiting the complementarity between optical remote sensing (which can be used to retrieve VCW by means of a radiative transfer model, PROSAIL) and VOD, which has the advantage over optical remote sensing products that it does not saturate at dense vegetation. Inferred VCW will be evaluated against ground measurements where they exist. The developed VCW will be applied globally alongside existing products including atmospheric formaldehyde concentrations, whose emission by plants is enhanced under stress, to identify vegetation drought hotspots and quantify drought impacts on gross primary production. These insights will be supported by simulations from an improved ecosystem model, enhanced by the satellite-derived VCW. The project takes an interdisciplinary approach, by combining the expertise of the host in vegetation ecophysiology and primary production modelling with the applicant’s well-developed skills in both optical and microwave remote sensing. It will contribute both to the improved utilization of data from existing satellites, and to the improvement of “next-generation” primary production models that depend strongly on both first-principles theory and extensive, space- and ground-based data on key ecosystem properties.