Understanding the role of drought timescales on vegetation dynamics

The ecology and stability of tropical savannas are of scientific importance due to their dominant role in the global carbon cycle, susceptibility to drought, high biodiversity, and human dependence on the ecosystem services they provide. However, there is little information about the impact of prolonged and persistent droughts on the carbon uptake and phenology of these ecosystems. Satellite remote sensing is an essential tool for studying tropical savannas due to their continental coverage. This indispensability of remote sensing manifests itself not only in the large spatial coverage of Earth observation (EO) data, but also in the opportunities it offers for the multi-scalar and multi-temporal analysis necessary to study these complex ecosystems. This project harnesses this opportunity through innovative use of state-of-the-art EO data and derived products from the European Copernicus program, and the European Space Agency’s Climate Change Initiative. In addition to EO data, this project will integrate site-level biometeorological data from the FLUXNET network.

Figure 1: The impact of two biophysical controls, plant-available water and vapor pressure deficit, on green-up and brown-down phenology at three sites located in a Sahelian savanna ecosystem. The partial correlation analysis revealed that the incre…

Figure 1: The impact of two biophysical controls, plant-available water and vapor pressure deficit, on green-up and brown-down phenology at three sites located in a Sahelian savanna ecosystem. The partial correlation analysis revealed that the increase in carbon uptake (i.e. gross primary production) during the greening phase, shortly after the onset of the first rains, is governed by the concurrent availability of plant-available water and reduction in vapor pressure deficit. Whereas the browning phase was characterized by a steep increase in vapor pressure deficit due to the cessation of the rains and a corresponding decrease in plant-available water and gross primary production. Read more here.

Preliminary results

We identified the main biophysical limitations that induce vegetation water stress in Sahelian savannas and evaluated the relationships between field data and Earth observation-derived spectral data for modeling vegetation carbon uptake  (i.e. gross primary production, GPP). We found that soil moisture-driven plant-available water (PAW) and vapor pressure deficit (VPD) together control the GPP of vegetation in the semi-arid African Sahel through their impact on the greening and browning phases (Figure 1). The partial correlation analysis revealed that the increase in carbon uptake during the greening phase, shortly after the onset of the first rains, is governed by the availability of PAW and a reduction in VPD. The increase in soil moisture also decreases land surface temperature (Spearman’s Rho, rs = −0.28) due to evaporative cooling. The browning phase is characterized by a steep decrease in GPP and a reduction in PAW due to a cessation of the rains.

If your current research aligns with this project, please don’t hesitate to contact me for possible collaboration

Funding: Swedish Research Council, grant 2018-00430

Duration: July 2019 - December 2022

Output: