Representation of disturbance in the Joint UK Land Environment Simulator Vn4.8 (JULES)
Geoscientific Model Development Discussions
<p><strong>Abstract.</strong> The representation of disturbance is a critical factor in land-surface modelling, but is generally poorly constrained in carbon cycle models. In particular, land-use change and fire can be treated as large-scale disturbances without full representation of their underlying complexities and interactions. Here we describe developments to the land surface model JULES (Joint UK Land Environment Simulator) to represent land-use change and fire as separate disturbances.
... ate disturbances. We use the HYDE (History Database of the Global Environment) land cover dataset to analyse the impact of land-use change on global vegetation, and couple the fire model INFERNO (INteractive Fire and Emission algoRithm for Natural envirOnments) to dynamic vegetation within JULES to assess how the representation of disturbance affects the simulation of present day vegetation. We test model performance, evaluating the inclusion of land use and fire disturbance against standard benchmarks. Using the Manhattan Metric, overall disturbance improves the simulation of vegetation cover compared to observations by up to 53<span class="thinspace"></span>%. Grasses show an improvement of up to 52<span class="thinspace"></span>%, with biases in extent reduced from &minus;66<span class="thinspace"></span>% to 13<span class="thinspace"></span>%. Total woody cover improves by up to 121<span class="thinspace"></span>% from a reduction in forest extent in the tropics, although simulated tree cover is now too sparse in some areas. Disturbance generally decreases tree and shrub cover and increases grasses. The results show that the disturbances provide important contributions to the realistic modelling of vegetation on a global scale, although in some areas fire and land-use together result in over-disturbance. This work provides a substantial contribution towards representing the full complexity and interactions between land-use change and fire that could be used in Earth System Models.</p>