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 and

carbon 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 realism

of forests drought response in the LSMs. CEROBI will address this problem by using carbon isotopes in tree rings and in the atmosphere to

constrain model parameters related to ecosystem response and resilience to droughts. This objective will be achieved through four key steps using

the ORCHIDEE LSM, although the methods developed throughout the project will be applicable to any LSM. First, I will add a few missing processes

required to fully represent the carbon isotopic composition of tree rings in LSMs. Second, I will eval-uate the drought response and

resilience of forests in ORCHIDEE using various kind of carbon isotope data. Third, I will identify the key model parameters controlling the drought

response. Finally, using Bayesian techniques, I will assimilate carbon isotopes measurements at eddy-covariance sites and in tree-rings to calibrate

these key model parameters. The newly calibrated ORCHIDEE LSM will be run globally during the period 2000-2100 under a range of

Shared Socioeconomic Pathways CO2 emissions scenario to assess the long-term impact of droughts on the carbon and water cycles. The project

is designed to exert my skills in atmospheric photosynthetic tracers and to develop my knowledge of ecosystem processes while generating highimpact

results. The fellowship will be a springboard to become an independent leading researcher in the fields of the carbon and water cycles.