How does drought impact burned area in Mediterranean vegetation communities?

Abstract

Drought and water stress are widely known to influence fuel moisture content and flammability, although differences do exist according to the response mechanisms and adaptive traits displayed by plant communities. In the Mediterranean basin, as a result of climate change, extreme drought events are expected to become more frequent and severe, envisaging episodes of increased fire risk. In this paper, we expand the scale of analysis on how does drought influence wildfire incidence exploring the joint influence on burned area of drought duration, magnitude and temporal distribution, and the affected vegetation communities (VCs). We leveraged the weekly adaptation of the Standardized Precipitation Evapotranspiration Index (SPEI) and historical fire perimeters to model complex interactions between drought and burned area mediated by VC composition and structure. We applied multivariate factor analysis (multi-group Principal Component Analysis) and non-parametric mixed regression models (GAMM) to a set of 1-to-48 weeks SPEI and 10 dominant VCs. We detected a significant influence of drought events (negative SPEI) on burned area, although differences in terms of seasonal distribution and VC were observed. Drought played a major role in explaining burned area in late spring and autumn by altering the usual positive rainfall-evapotranspiration balance, suggesting a potential lengthening of the fire season given the projected drought trends in the next decades.