Description of the "TRIFFID" Dynamic Global Vegetation Model

Abstract

This note describes the terrestrial carbon cycle component of the Hadley Centre's coupled climate-carbon cycle model (Cox et al (2000)). \TRIFFID (Top-down Representation of Interactive Foliage and Flora Including Dynamics) is a dynamic global vegetation model, which updates the plant distribution and soil carbon based on climate-sensitive CO2 uxes at the land-atmosphere interface. The surface CO2 uxes associated with photosynthesis and plant respiration are calculated in the MOSES 2 tiled land-surface scheme (Essery et al (In preparation)), on each atmospheric model timestep (normally 30 minutes), for each of 5 plant functional types. The area covered by a plant type is updated (normally every 10 days) based on the net carbon available to it and on the competition with other plant types, which is modelled using a Lotka-Volterra approach. Soil carbon is increased by litterfall, which can arise from local processes such as leaf-drop as well as large-scale disturbances which reduce the vegetated area. Soil carbon is returned to the atmosphere by microbial respiration which occurs at a rate dependent on soil moisture and temperature. TRIFFID has been designed to allow economical diagnosis of initial states using a Newton-Raphson descent towards the equilibrium state consistent with a given climate.