Constraining forEst Responses to drOughts with carBon Isotopes

The increasing frequency and intensity of droughts in response to climate change threaten the capability of forests to act as climate regulators andcarbon sinks. Currently, Land Surface Models (LSMs), the terrestrial components of climate models used to make climate projections,underestimate severity of and the recovery time from droughts. Therefore, credible and reliable climate projections, require improving the realismof forests drought response in the LSMs. CEROBI will address this problem by using carbon isotopes in tree rings and in the atmosphere toconstrain model parameters related to ecosystem response and resilience to droughts. This objective will be achieved through four key steps usingthe ORCHIDEE LSM, although the methods developed throughout the project will be applicable to any LSM. First, I will add a few missing processesrequired to fully represent the carbon isotopic composition of tree rings in LSMs. Second, I will eval-uate the drought response andresilience of forests in ORCHIDEE using various kind of carbon isotope data. Third, I will identify the key model parameters controlling the droughtresponse. Finally, using Bayesian techniques, I will assimilate carbon isotopes measurements at eddy-covariance sites and in tree-rings to calibratethese key model parameters. The newly calibrated ORCHIDEE LSM will be run globally during the period 2000-2100 under a range ofShared Socioeconomic Pathways CO2 emissions scenario to assess the long-term impact of droughts on the carbon and water cycles. The projectis designed to exert my skills in atmospheric photosynthetic tracers and to develop my knowledge of ecosystem processes while generating highimpactresults. The fellowship will be a springboard to become an independent leading researcher in the fields of the carbon and water cycles.