Investigating the impact of different drought-heat signatures on carbon dynamics using a dynamic global vegetation model

Droughts and heat waves have large impacts on the terrestrial carbon cycle. They lead to reductions in gross and net carbon uptake or anomalous increases in carbon emissions to the atmosphere because of responses such as stomatal closure, hydraulic failure and vegetation mortality. The impacts are particularly strong when drought and heat occur at the same time. Climate model simulations diverge in their occurrence frequency of compound hot and dry events, and it is unclear how these differences affect carbon dynamics. Furthermore, it is unknown whether an increase in frequency of droughts and heat waves leads to long-term changes in carbon dynamics, and how such an increase might affect vegetation composition.

To study the immediate and long-term effects of varying signatures of droughts and heat waves on carbon dynamics such as inter-annual variability of carbon fluxes and cumulative carbon uptake, we employ the state-of-the-art dynamic global vegetation model LPX-Bern (v1.4) under different drought-heat scenarios.

We have constructed five 100-yr long scenarios with different drought-heat signatures, representing a “control”, “close to mean seasonal cycle”, “drought only”, “heat only”, and “compound drought and heat” climate forcing to LPX-Bern. This is done by sampling daily climate variables from a 2000-year stationary simulation of a General Circulation Model (EC-Earth) for present-day climate conditions. Such a sampling ensures physically-consistent co-variability between climate variables in the climate forcing.

We investigate the carbon-cycle response and changes in vegetation structure to different drought-heat signatures on a global grid, representing different land cover types and climate zones. Our results provide a better understanding of the links between hot and dry conditions and carbon dynamics. This may help to reduce uncertainties in carbon cycle projections, which is important for constraining carbon cycle-climate feedbacks.