Abstract
The distribution of fire on Earth has been monitored from space for several decades, yet the geography of global fire regimes has proven difficult to reproduce from interactions of climate, vegetation, terrain, land use and other human activities by empirical and process-based fire models. Here, we propose a simple, yet robust, model for the global distribution of fire potential based on fundamental biophysical constraints controlling fire activity in all biomes. In our ‘top-down’ approach we ignored the dynamics of individual fires and focus on capturing hydroclimatic constraints on the production and (seasonal) desiccation of fuels to predict the potential mean annual fractional burned area at 0.25° spatial resolution, here estimated by the 0.99 quantile of the observed mean annual fractional burned area () over the 1995-2016 period of the Global Fire Emissions Database (GFED4). We show that 80% of the global variation in can be explained from a combination of mean annual precipitation and potential evapotranspiration. The proposed hydroclimatic model reproduced observed 0.99 quantile fire activity levels equally well across all biomes and provided the first objective underpinning for the dichotomy of global fire regimes in two domains characterised by either fuel production limitations on fire or fuel dryness limitations on fire. A sharp transition between the two climate-fire domains was found to occur at a mean annual aridity index of 1.9 (1.94 ± 0.02). Our model provides a simple but comprehensive basis for predicting fire potential under current and future climates, as well as an overarching framework for estimating effects of human activity via ignition regimes and manipulation of vegetation.
Highlights
Satellite-based Earth observation is providing an increasingly accurate picture of global fire patterns [1,2,3,4]
The highest fire activity is observed in seasonally drytropical environments of South America, Africa and Australia, but fires occur with varying frequency, intensity and seasonality in almost all biomes on Earth [5]
Building on the methods developed in a previous study of Australian fire regimes [19], we propose a new global model that predicts the long term upper limit of the mean annual fractional burned area, F0.99, from two basic hydroclimatic variables: mean annual precipitation, P, and potential evapotranspiration, E0
Summary
Satellite-based Earth observation is providing an increasingly accurate picture of global fire patterns [1,2,3,4]. Most current land surface models (LSMs) and Dynamic Global Vegetation Models (DGVMs) have some capacity to simulate fire activity from basic environmental variables but predictions [8, 10] usually only agree with observations in some biomes (e.g. savannas of the Sub-Saharan Africa), while disagreeing in others (e.g. boreal forests of North-America). The limited ability of current models in predicting global fire patterns suggests that their fire modules fail to capture some aspects of the biophysics that control fire activity across different environments. Incomplete understanding of biophysical drivers and constraints that underlie current global fire patterns creates uncertainty in model predictions of how fire regimes, fire-prone ecosystems and related biogeochemical cycles may respond to rising atmospheric [CO2] and climate change [15]
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