Tracing devastating fires in Portugal to a snow archive in the Swiss Alps: a case study
<p>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...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
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| Series: | The Cryosphere |
| Online Access: | https://tc.copernicus.org/articles/14/3731/2020/tc-14-3731-2020.pdf |
| Summary: | <p>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) analysed 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)
analysed the fire spread, its spatial and temporal extent, and its
intensity with remote-sensing (e.g. MODIS) Active Fire and Burned Area products. According to modelled emissions of the FINN v1.6 database, the
fire emitted a total amount of 203.5 t BC from a total burned area of 501 km<span class="inline-formula"><sup>2</sup></span> as observed on the basis of satellite fire products. Backward
trajectories unambiguously linked a peak of atmospheric-equivalent BC
observed at the Jungfraujoch research station on 22 June – with
elevated levels until 25 June – with the highly intensive fires in
Portugal. The atmospheric signal is in correspondence with an outstanding
peak in microscopic charcoal observed in the snow layer, depositing nearly
as many charcoal particles as during an average year in other ice archives.
In contrast to charcoal, the amount of atmospheric BC deposited during the
fire episode was minor due to a lack of precipitation. Simulations with a
global aerosol-climate model suggest that the observed microscopic
charcoal particles originated from the fires in Portugal and that their
contribution to the BC signal in snow was negligible. Our study revealed
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.
The findings are important for future ice-core studies as they document
that, for BC as a fire tracer, the signal preservation<span id="page3732"/> depends on precipitation.
Single events, like this example, might not be preserved due to unfavourable
meteorological conditions.</p> |
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| ISSN: | 1994-0416 1994-0424 |