Preview

PDF, English - main document Download (29MB) | Terms of use

Abstract

The land carbon sink partly mitigates climate change by taking up one third of the anthropogenic fossil fuel CO2 emissions every year. Semiarid ecosystems contribute significantly to the interannual dynamics of the land sink. However, state-of-the-art land-atmosphere CO2 flux estimates by in situ measurement-based atmospheric inversions and dynamic global vegetation models (DGVMs) show large uncertainties for semiarid regions in the Southern Hemisphere. This cumulative thesis demonstrates the potential of satellite data to improve regional CO2 flux estimates in the Southern Hemisphere and to be used as an atmospheric constraint to evaluate DGVMs. CO2 fluxes based on the Greenhouse Gases Observing Satellite (GOSAT) for 2009 - 2018 are evaluated in three study regions in Australia, southern Africa, and South America. Vegetation processes driving the flux dynamics are identified by using DGVMs that align well with the GOSAT-based fluxes. We find that ecosystem respiration responding to soil moisture and soil rewetting drives seasonal and interannual variability in the carbon cycle in semiarid regions. This work calls for improving the representation of soil rewetting processes in DGVMs to accurately model the carbon dynamics in semiarid regions and thereby reduce uncertainties of the global carbon budget and enable more accurate projections of climate-carbon feedbacks.