Excessive fire occurrence in Romania from 2001 to 2022: Trends and drivers across ecoregions and land cover classes

Wildfire is an integral part of temperate ecosystems, but human activities have significantly altered fire regimes, including frequency, size, intensity and seasonality. Romania, located in central-eastern Europe, recently exhibited the highest biomass burning in Europe. However, little is known of the trends and determinants of fire recurrence, apart from the common use of fire to clear crop residues on arable land. This study utilizes satellite-based fire data (FIRMS) from 2001 to 2022 and land cover maps (CORINE) to investigate temporal trends in fire occurrence across ecoregions and land cover types in Romania and identify those most susceptible to fire.Over 2001-2022, Romania witnessed a total of 0.44 fires/ km² averaging 0.02 fires/km²/yr. Our analysis revealed a declining trend in fire occurrence along an elevation gradient, from plains to hills, plateaus and mountains, aligning with the prevalence of the dominant land cover classes and climatic gradients. Agricultural land cover types demonstrated the highest fire incidence, with arable land exhibiting the highest rate (0.04 fires/km²/yr) and forests the lowest (below 0.01 fires/km²/yr). Following the accession of Romania to the EU in 2007 and the prohibition of agricultural fires, a reduction in burning on arable land (crop residues) can be observed, while the use of fire in other agricultural classes persisted or even increased, indicating a more complex effect of socio-economic developments on fire pattern. Specifically, areas more marginal for agriculture, such as complex agricultural fields interspaced with housing and natural vegetation continued to employ fire as a management tool.Natural land cover classes, such as wetlands principally occupying the Danube Delta (0.06 fires/km²/yr) and natural grasslands (0.01 fires/km²/yr), also experienced substantial fire occurrences and an intensification in more recent periods. Given the rarity of naturally ignited fires (lightning) in Romania, the intentional use of fire to clear dry reed biomass for land regeneration appears to be prevalent also in moist areas. Remarkably, broadleaved and mixed forests burned more frequently than coniferous forests despite the latter having traits to convey high flammability and burn with high frequency. This feature suggests that fires in broadleaved forests, predominant at low and mid elevations, likely expanded from neighbouring agricultural lands.Crucially, our analysis highlights that years with elevated fire occurrence coincide with extreme droughts and heatwaves (e.g., 2012, 2015), emphasizing the influence of extreme climate conditions in accelerating fire episodes and the spread of fires initiated in agricultural areas into natural and semi-natural habitats. Given the substantial occurrence of fires in agricultural land but also in natural habitats, such as wetlands and grasslands in Romania, research investigating the risks and vulnerability of these habitats to fire should be prioritized.