Tracing devastating fires in Portugal to a snow archive in the Swiss Alps: a case study

• Main Authors: Osmont, Dimitri, Brugger, Sandra, Gilgen, Anina, Weber, Helga, Sigl, Michael, Modini, Robin L., Schwörer, Christoph, Tinner, Willy, Wunderle, Stefan, Schwikowski, Margit
• Format: Text
• Language: English
• Published: 2020
• Subjects: ice core
• Online Access: https://doi.org/10.5194/tc-2020-58; https://tc.copernicus.org/preprints/tc-2020-58/

Recent large wildfires, such as those in Portugal in 2017, have devastating impacts on societies, economy, ecosystems and environments. However, wildfires are a natural phenomenon, which has been exacerbated by land use during the past millennia. Ice cores are one of the archives preserving information on fire occurrences over these timescales. A difficulty is that emission sensitivity of ice cores is often unknown, which constitutes a source of uncertainty in the interpretation of such archives. Information from specific and well-documented case studies is therefore useful to better understand the spatial representation of ice-core burning records. The wildfires near Pedrógão Grande in Central Portugal in 2017 provided a test bed to link a fire event to its footprint left in a high-alpine snowpack considered a surrogate for high-alpine ice-core sites. Here, we (1) analyzed black carbon (BC) and microscopic charcoal particles deposited in the snowpack close to the high-alpine research station Jungfraujoch in the Swiss Alps, (2) calculated backward trajectories based on ERA-Interim reanalysis data and simulated the transport of these carbonaceous particles using a global aerosol-climate model, and (3) analyzed the fire spread, its spatial and temporal extent, as well as its intensity, with remote sensing (e.g. MODIS) active fire and burned area products. A peak of atmospheric equivalent BC (eBC) observed at the Jungfraujoch research station on 22 nd June, with elevated eBC levels until the 25 th June, is in correspondence with a peak in refractory BC (rBC) and microscopic charcoal observed in the snow layer. rBC was mainly scavenged by wet deposition and we obtained scavenging ratios ranging from 81 to 91. Unlike for microscopic charcoal, the model did not well reproduce the observed rBC signal. Our study reveals that microscopic charcoal can be transported over long distances (1500 km), and that snow and ice archives are much more sensitive to distant events than sedimentary archives, for which the signal is dominated by local fires. Microscopic charcoal concentrations were exceptionally high since this single outstanding event deposited as many charcoal particles per day as during an average year in ice cores. This study unambiguously links the fire tracers in the snow with the highly intensive fires in Portugal, where a total burned area of 501 km 2 was observed on the basis of satellite fire products. According to our simulations, this fire event emitted at least 203.5 tons of BC.