Exploring the atmospheric conditions increasing fire danger in the Iberian Peninsula

The fire danger is particularly sensitive to meteorological conditions. The present study discusses the atmospheric conditions during three periods to evaluate how they can increase fire danger. A set of three convection-permitting simulations was configured at 2.5 km resolution using the Meso-NH model. In the first period, the intense surface heating induced by a heatwave favoured the development of the Iberian thermal low in July 2019, leading to the formation of precipitating systems and resulting in convective outflows that affected the central Iberian Peninsula. The outflows were shown to be an important feature in evaluating fire danger during the period; however, the simulation also highlighted the orographic effect as another phenomenon playing an important role in fire development and consequently enhancing the fire danger in some regions such as in the extreme southwest of Portugal. The orographic effect in this specific region was identified and analyzed in detail for two megafire events that occurred in Monchique in August 2003 and 2018. The Monchique Mountain's shape and orientation interacting with the airflow induced upslope and downslope winds that favoured the rapid propagation of the fire fronts in August 2018. The third experiment showed that the circulation of a sea breeze from the southern coast of Portugal may act as an enhancer for fire danger in the region when interacting with the regional mountain, such as verified in the 2003 megafire. The study shows that the fire danger over specific regions can be increased by different atmospheric phenomena and explored from atmospheric modelling. The convective outflows were an important factor enhancing fire danger; however, the orographic effect was confirmed as the main factor producing two megafires events in the extreme southwest of Portugal. A set of three convection-permitting simulations was configured at 2.5 km resolution using the Meso-NH model to discuss the atmospheric conditions, which may lead to an increase in fire danger during the three periods. (a) Schematic represents some features identified in the three situations examined that could increase fire danger, namely outflow and orographic mechanism. (b) The downward motions, and convective outflow at the surface are represented by the vertical cross-section A-A'. The vertical cross-section B-B' corresponds to the different airflow configurations that affected Monchique Mountain, having been the key point to the development of two mega-fires observed in the region. The orographic effects were created in response to the surface-atmosphere interaction, namely producing downslope winds over Monchique Mountain: (c) in the southern slope and (d) northern slope. image