Savannas retain water better than grasslands in central Brazil: findings from a novel Sentinel-1 derived vegetation water content
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Proposed Symposium Title: Savannas retain water better than grasslands in central Brazil: findings from a novel Sentinel-1 derived vegetation water content
Paulo N. Bernardino 1 2, Rafael S. Oliveira 2, Koenraad Van Meerbeek 1, Marina Hirota 2 3, Mariana N. Furtado 2, Isabela A. Sanches 1, Ben Somers 1
Affiliations: 1 KU Leuven, Leuven, Belgium. 2 University of Campinas, Campinas, Brazil. 3 Federal University of Santa Catarina, Florianópolis, Brazil.
Assessing vegetation water content (VWC) dynamics is essential for understanding plant growth, water and carbon cycles, and ecosystems’ drought response and stability in the face of climate change. However, acquiring field-based VWC estimates, consistently through space and time, is challenging due to time and resource constraints. Therefore, in this study we explored the potential of Sentinel-1 Synthetic Aperture Radar (SAR) data for estimating VWC in natural ecosystems in central Brazil, ultimately using the generated VWC dataset to answer how the studied vegetation types (i.e., savannas, dry grasslands, and waterlogged grasslands) respond to seasonal dry periods in terms of water content. Field data from 82 plots, spanning various seasons and vegetation types, served to calibrate and validate the VWC estimation model. The calibrated model, with an R² of 0.519 and RMSE of 0.412 kg/m², was then applied to Sentinel-1 SAR backscatter data to generate monthly VWC maps for grassland and savanna ecosystems at 30 m spatial resolution between April 2015 and March 2023. These maps, combined with rainfall and potential evapotranspiration data, provided insights into how these ecosystems respond to water scarcity during dry seasons. More specifically, savannas showed to be able to retain higher water content levels during dry periods, likely attributed to their woody component's enhanced water-holding capacity and deep-root systems, enabling access to deeper groundwater. This research underscores the potential of Sentinel-1 SAR data for monitoring VWC in natural ecosystems, opening avenues for assessing ecosystem responses to drought events and alterations in their functioning, ultimately guiding informed land management decisions in the face of climate change.