Tropical climate–vegetation–fire relationships: multivariate evaluation of the land surface model JSBACH

Abstract

Abstract. The interactions between climate, vegetation and fire can strongly influence the future trajectories of vegetation in Earth system models. We evaluate the relationships between tropical climate, vegetation and fire in the global vegetation model JSBACH, using a simple fire scheme and the complex fire model SPITFIRE with the aim to identify potential for model improvement. We use two remote-sensing products (based on MODIS and Landsat) in different resolutions to assess the robustness of the obtained observed relationships. We evaluate the model using a multivariate comparison that allows us to focus on the interactions between climate, vegetation and fire and test the influence of land use change on the modelled patterns. Climate–vegetation–fire relationships are known to differ between continents; we therefore perform the analysis for each continent separately. The observed relationships are similar in the two satellite data sets, but maximum tree cover is reached at higher precipitation values for coarser resolution. This shows that the spatial scale of models and data needs to be consistent for meaningful comparisons. The model captures the broad spatial patterns with regional differences, which are partly due to the climate forcing derived from an Earth system model. Compared to the simple fire scheme, SPITFIRE strongly improves the spatial pattern of burned area and the distribution of burned area along increasing precipitation. The correlation between precipitation and tree cover is higher in the observations than in the largely climate-driven vegetation model, with both fire models. The multivariate comparison identifies excessive tree cover in low-precipitation areas and a too-strong relationship between high fire occurrence and low tree cover for the complex fire model. We therefore suggest that drought effects on tree cover and the impact of burned area on tree cover or the adaptation of trees to fire can be improved. The observed variation in the relationship between precipitation and maximum tree cover between continents is higher than the simulated one. Land use contributes to the intercontinental differences in fire regimes with SPITFIRE and strongly overprints the modelled multimodality of tree cover with SPITFIRE. The multivariate model–data comparison used here has several advantages: it improves the attribution of model–data mismatches to model processes, it reduces the impact of biases in the meteorological forcing on the evaluation and it allows us to evaluate not only a specific target variable but also the interactions.

Response of simulated burned area to historical changes in environmental and anthropogenic factors: a comparison of seven fire models

“…An alternative approach, given the complex interactions between climate and vegetation parameters, might be to disentangle the model signals using multivariate analysis (see e.g. Forkel et al, 2019a;Lasslop et al, 2018).…”

“…Global vegetation models are an important tool for examining the impacts of climate change and are used in policyrelevant contexts (IPCC, 2014;Schellnhuber et al, 2014;IPBES, 2016). Given the various influences of fire on the ecosystems (Bond et al, 2005), the carbon cycle and climate (Lasslop et al, 2019) improvements of global fire models are particularly important.…”

“…Analyses based on observations of the pre-industrial period suggest that the contribution of fire to the overall climatecarbon-cycle feedback is substantial with 5.6 ± 3.2 ppm K −1 CO 2 (Harrison et al, 2018) while the strength of the global land climate-carbon-cycle feedback estimated from Earth system simulations (Arora et al, 2013) is 17.5 ppm K −1 (Harrison et al, 2018). However, comparing potential fireinduced losses from terrestrial carbon pools and stocks of solid pyrogenic carbon in soils and ocean, fire may also be a net sink of carbon, and Earth system simulations show a negative effect of fire on radiative forcing (Lasslop et al, 2019). In addition to these consequences for the Earth system, wildfires directly impact society and economy (Gauthier et al, 2015), and human health can be seriously impaired (Johnston et al, 2012;Finlay et al, 2012).…”

“…Wildfires are an important driver of vegetation distribution and regulate ecosystem functioning, biodiversity and carbon storage over large parts of the world (Bond et al, 2005;Hantson et al, 2016a). Fire has strong impacts on climate through changing land surface properties, through atmospheric chemistry and hence radiative forcing and through biogeochemical cycling (Bowman et al, 2009;Randerson et al, 2012;Ward et al, 2012;Yue et al, 2016;Lasslop et al, 2019). Estimates of the net effect of fire on the Earth system vary.…”

Linking Vegetation-Climate-Fire Relationships in Sub-Saharan Africa to Key Ecological Processes in Two Dynamic Global Vegetation Models

“…Results of such models are useful to inform the general public but also policy makers. However, many DGVMs display high uncertainties in predicting the distribution of current tropical vegetation biomes, and especially of grasslands and savannas, possibly due to the way they represent the natural ecological mechanisms and feedbacks between vegetation, climate and fire (Baudena et al, 2015;Lasslop et al, 2018).…”