The role of the land surface in the global carbon and water cycles

The global continental carbon and water cycles are intimately linked through stomatal regulation during vegetation photosynthesis and biosphere-atmosphere interactions. Therefore, to have a complete understanding of both present and future climate, these cycles must be studied as an interconnected system. This thesis presents three studies that aim to better explain these interactions and provide a direction forward for improved model projections of climate. The first study shows that biosphere-atmosphere feedbacks can contribute up to 30% of climate and weather variability in certain regions that help determine the net CO2 balance of the biosphere. It demonstrates that Earth System Models are under-estimating these contributions, mainly due to the underestimation of the biosphere response to radiation and water availability. It emphasizes the importance of correctly capturing these feedbacks in models for accurate subseasonal to seasonal climate predictions. The second demonstrates that changes in soil moisture (both short-term variability and long-term trends) strongly limit the ability of the continents to act as a carbon sink, with overall effects on the same order of magnitude