Relating wildfire seasonality to remotely sensed fuel phenology: a tool for a new pyrogeography?

Abstract

In the Mediterranean region, notwithstanding the high human pressure, fire activity is essentially drought-driven, such that fuel moisture represents the main determinant for sustaining fire ignition and spread. Seasonal variations in remotely sensed vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), proved to be indicative of variations in fuel amount and moisture content and associated fire risk. This study aims to propose a general method to represent the combined pattern of remotely sensed vegetation indices and fire ignitions throughout the year, as potential tool to classify terrestrial ecosystems at local to global scale. To jointly visualize the temporal dynamics of remotely sensed vegetation indices and annual fire density, we propose to log-transform the ‘annual fire density’ (AFD) values, thus expressing the temporal dynamics of fire ignitions in orders of magnitude and producing a pyrophenological diagram in which both quantities vary approximately in the same range. The methodological approach proposed in this study proved to be independent of the local characteristics and applicable with any available remotely sensed vegetation index. The combined NDVI-fire diagrams may contribute to the global pyrophenological classification and mapping of terrestrial ecosystems based on the integrated monitoring of remotely sensed vegetation phenology and fuel seasonality.