Remote Sensing Indicators of Green Water in Mediterranean Croplands, Forests, and Agroforestry Systems: A Multi-Year Study from Tunisia

The plant-water-atmosphere interaction is partly acknowledged as “Green Water” (GW) in the planetary boundaries concept (Wang-Erlandsson et al. 2022). There, the soil moisture in the root-zone is estimated with global models and assumptions about the root depth, plant cover, drought indices and other low-resolution proxies. This study aims to evaluate Green Water with remote sensing data from Sentinel-2 by combining the Normalized Difference Moisture Index (NDMI), vegetation indices, drought indices and detailed information about the LULC down to the species level.

The study’s focus is on seasonal characteristics like moisture retention in the dry season, recovery/water uptake after rainfall and stand vulnerability to drought events. The moisture index (NDMI) and Soil adjusted Vegetation Index (SAVI) will show these seasonal differences of GW and plant health on the aridity gradient in Tunisia.

We expect that

• there are differences in water retention capacities between the land cover types (agriculture – agroforestry – forest plantations)
• species (olive and carob in agroforestry, eucalyptus and pine in forests) show different water retention capabilities and vigor in the dry season.
• these differences will lead to unequal microclimatic effects like surface temperature and latent heat flux.

The results can be used to estimate other ecosystem services related to GW and living plant matter as well as the improvement of model inputs to go beyond mere plant functional types.