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The role of wind direction on the occurrence of large fire events in Portugal
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Resumo(s)
Large wildfires have been landmark events in continental Portugal during the last decades, producing
catastrophic damages and shaping the socio-economics of the country. In this work, the role of the wind
field in wildfires in the last two decades is analyzed to assess the role in triggering or exacerbating these
events. Furthermore, this thesis reinforces the need to incorporate information about wind direction in
meteorological fire danger indexes.
Two intra-annual peaks of fire activity were found, a mostly human-inflicted smaller peak in March
and a major one in the summer period. No significant relation was found between the number of ignitions
and burned area, akin to previous studies. Spatially, it was found that ignitions are more frequent in
highly populated areas, whereas the larger burned areas are found in the inland, with dense forestation
and less population. This discrepancy translates into the fact that only 0.06% of ignitions accounted for
nearly 50% of all burned area. The meteorological fire danger, through the Fire Danger Index (FWI),
was analyzed per ignition observation, with ignitions which individually originated burned areas above
1000 ha being markedly associated to the conditions of higher fire danger.
Analysis of the wind field in continental Portugal during the warmest period of the year presented a
strong northwesterly component while days with more than 1000 ha of burned area, had a prevalence of
easterly winds in the ignition points. Principal component analysis was used to identify long shape
wildfires, which were furthermore associated with the most intense winds. Considering the wildfires
which had their prevalent direction and wind field direction closely aligned (forming an angle less than
45º), they represent 24.2% of all burned area for the 2001-2020 period, although corresponding to only
0.03% of all ignitions. These mostly occur where topography is more complex, in inland Portugal.
Descrição
Tese de mestrado, Ciências Geofísicas (Meteorologia e Oceanografia), 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Grandes fogos Direção do vento Perigo de incêndio Potência radiativa de fogo ERA5 Teses de mestrado - 2023