Representation of fire, land-use change and vegetation dynamics in the Joint UK Land Environment Simulator vn4.9 (JULES)

Chantelle Burton,Ted R Feldpausch,Douglas I Kelley,Andy Wiltshire,Chris D Jones,Manoel Cardoso,Eddy Robertson,Richard Betts,Anna Harper

doi:10.5194/gmd-12-179-2019

Abstract

Abstract. Disturbance of vegetation is a critical component of land cover, but is generally poorly constrained in land surface and 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 distinct processes which interact with simulated vegetation dynamics. We couple the fire model INFERNO (INteractive Fire and Emission algoRithm for Natural envirOnments) to dynamic vegetation within JULES and use the HYDE (History Database of the Global Environment) land cover dataset to analyse the impact of land-use change on the simulation of present day vegetation. We evaluate the inclusion of land use and fire disturbance against standard benchmarks. Using the Manhattan metric, results show improved simulation of vegetation cover across all observed datasets. Overall, disturbance improves the simulation of vegetation cover by 35 % compared to vegetation continuous field (VCF) observations from MODIS and 13 % compared to the Climate Change Initiative (CCI) from the ESA. Biases in grass extent are reduced from −66 % to 13 %. Total woody cover improves by 55 % compared to VCF and 20 % compared to CCI from a reduction in forest extent in the tropics, although simulated tree cover is now too sparse in some areas. Explicitly modelling fire and land use 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 too much 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.

Highlights

JULES (Joint UK Land Environment Simulator) is a land surface model (LSM) which simulates surface fluxes of water, energy and carbon, along with the state of terrestrial hydrology, vegetation and carbon stores (Clark et al, 2011; Best et al, 2011)
The introduction of Land-use and land cover change (LULCC) generally results in a reduction in broadleaf, needle-leaf and shrub vegetation and an increase in C3 and C4 grasses (Fig. 1, fourth column), improving the simulation of vegetation cover by 23 % compared to vegetation continuous field (VCF) and 17 % against Climate Change Initiative (CCI) (Table 4)
This work has described the first steps in developing the land surface model JULES to represent fire and land use as separate disturbances

Summary

Introduction

JULES (Joint UK Land Environment Simulator) is a land surface model (LSM) which simulates surface fluxes of water, energy and carbon, along with the state of terrestrial hydrology, vegetation and carbon stores (Clark et al, 2011; Best et al, 2011). We document updates to the calculation of vegetation cover, including spatially and temporally varying changes in land use, and introduce a new disturbance term from fire based on the fire model INFERNO (Mangeon et al, 2016) as separate from the large-scale disturbance factor for the first time in JULES. We use these processes together with dynamic vegetation to address the impact on global vegetation cover

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