Identifying wildfire-prone atmospheric circulation weather types on mainland Spain

Abstract In this paper we present a detailed spatial assessment of the association between atmospheric synoptic conditions (the weather types, WT) and fires on the Spanish mainland. The WT approach allows the continuum of atmospheric fields to be compressed into a few comprehensive patterns, providing meaningful information on the movement of air masses, wind direction and, ultimately, wind speed. We analyzed a total of 291,547 individual fires from the official Spanish Fire database (1974–2014) and corresponding daily WT patterns on the Iberian Peninsula from the daily NCEP/NCAR Reanalysis database, 1951–2015. Underlying spatial patterns of association among fire and weather types were explored by means of self-organizing maps (SOM) coupled to hierarchical clustering. Our analyses have detected that fires tend to occur and become largermore likely under certain atmospheric conditions suggesting that specific weather patterns can promote or boost fire events. From a pyrogeographical point of view, the contribution of WTs to wildfires on the Spanish mainland seems to be highly diverse, and displays several temporal and spatial patterns. The northwest region responds mostly to eastern flows during summer and southern during winter. Fires in the northern Mediterranean coast are promoted by northerly flows while in southern regions fires are linked to C or SE extreme heat episodes during summer. Overall, fires activity usually increases in the lee ward of mountain ranges depending on the prevalent flow from WTs, and thus related to adiabatic heating of the air flow.