Increasing trends in fire severity and drought conditions in west-central Spain (1985-2017)

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Natalia Quintero, Olga Viedma and José M. Moreno, Department of Environmental Sciences, University of Castilla-La Mancha, Toledo, Spain

Background/Question/Methods and Results/Conclusions
• Background: Climate conditions are changing across the world, including the Mediterranean region. It is important to determine how fire activity (frequency and size) and fire severity (from RBR Landsat family) is responding to such changes.
• Question: We are aimed to identify temporal changes in fire activity and fire severity on main vegetation types in west central Spain from 1985 to 2017; and their association with climate conditions during prefire water year (October-May), prefire spring (March-May) and summer season (June-September).
• Methods and Results: To accomplish these objectives we analyzed trends, breakpoints and periods; and used autoregressive moving average (ARMA) models to explain and predict historical fire variables by climate conditions using stationary time series. Main results showed that fire number and burned area has decreased whereas fire severity and drought conditions have increased in the last decades. Wildfires tended to burn preferentially treeless areas. Flammable pine areas burned less, while shrublands burned more. Mean fire severity (RBR) increased as well as p5 and p90 RBR values. The percentage of burned area in low severity (RBR < 100) lowered whereas the percentage in moderate severity (RBR 100-300) increased. All vegetation types burned at higher severity over time (higher mean RBR and p90 values, and higher percentage of burned area at high severity [RBR ≥ 300]) whereas deciduous forests burned less at low severity. This decreasing fire activity but with increasing fire severity coincides with a rising warmer and drought conditions (air temperature increased whereas rainfalls and soil humidity decreased).
• Conclusions: Temporal behavior of fire activity and fire severity were highly explained and fairly predicted by climate conditions during previous months (prefire October-May and spring) and summer season. Based on that, warmer and drier prefire- and summer seasons corresponded to higher RBR fire severity values, and higher proportion of burned area at high severity, boosting fire risk in future.