Abstract. The frequency and intensity of summer droughts and heat waves in Western Europe have been increasing, raising concerns about the emergence of fire hazard in less fire prone areas. This exposure of old-growth forests hosting unadapted tree species may cause disproportionately large biomass losses compared to those observed in frequently burned Mediterranean ecosystems. Therefore, analyzing fire seasons from the perspective of exposed burned areas alone is insufficient, we must also consider impacts on biomass loss. In this study, we focus on the exceptional 2022 summer fire season in France and use very high-resolution (10 m) satellite data to calculate the burned area, tree height at the national level, and the subsequent ecological impact based on biomass loss during fires. Our high resolution semi-automated detection estimated 42,520 ha of burned area, compared to the 66,393 ha estimated by the European automated remote sensing detection system (EFFIS), including 48,330 ha actually occurring in forests. We show that Mediterranean forests had a lower biomass loss than in previous years, whereas there was a drastic increase in burned area and biomass loss over the Atlantic pine forests and temperate forests. High biomass losses in the Atlantic pine forests were driven by the large burned area (28,600 ha in 2022 vs. 494 ha yr−1 in 2006–2021 period) but mitigated by a low exposed tree biomass mostly located on intensive management areas. Conversely, biomass loss in temperate forests was abnormally high due to both a 15-fold increase in burned area compared to previous years (3,300 ha in 2022 vs. 216 ha in the 2006–2021 period) and a high tree biomass of the forests which burned. Overall, the biomass loss (i.e. wood biomass dry weight) was 0.25 Mt in Mediterranean forests and shrublands, 1.74 Mt in the Atlantic pine forest, and 0.57 Mt in temperate forests, amounting to a total loss of 2.553 Mt, equivalent to a 17 % increase of the average natural mortality of all French forests, as reported by the national inventory. A comparison of biomass loss between our estimates and global biomass/burned areas data indicates that higher resolution improves the identification of small fire patches, reduces the commission errors with a more accurate delineation of the perimeter of each fire, and increases the biomass affected. This study paves the way for the development of low-latency, high-accuracy assessment of biomass losses and fire patch contours to deliver a more informative impact-based characterization of each fire year.

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INTRODUCTION • Even if the agricultural fires correspond to a high proportion of burned areas, their inventory is insufficient. • Considering the central role of agriculture in France, understanding agricultural fire regimes appears to be central to the objective of food security. • Most cropland or rangeland fires are directly or indirectly related to human activities, facilitating their control. MATERIEL AND METHODS • A data mining analysis of non-scientific literature was conducted between 2000 and 2021 to study the temporal and spatial evolution of agricultural fires. • This database is compared to MODIS hotspots in order to validate this active detection method and to define its limits. • An estimate of the carbon footprint is made at the French level. RESULTS • The data mining study allowed the inventory of more than 500 fire events per year. • The high spatial heterogeneity of agricultural fires is mostly explained by the variation of crop types across the territory as well as by topoclimatic conditions. • Some years, such as 2003 and 2009, are characterized by a particularly large number of agricultural fires, linked to strong heat waves. • Crop fires occur primarily during the summer months when weather and fuel conditions are most favorable. Pasture fires, mainly prescribed fires, occur before and after winter to limit their spread. Building fires occur throughout the year. DISCUSSION • This first attempt at inventorying agricultural fires in France allowed us to describe spatial and temporal patterns specific to these types of fires. • Carbon emissions from these fires are currently largely underestimated and contribute to a significant proportion of the national carbon budget.