Circulation weather types and wildland forest fires in the western Iberian Peninsula

The use of six indices associated with geostrophic wind and vorticity has allowed a classification of circulation weather types to be determined. This classification was employed to study the impact of low-level circulations at low levels on the daily number of forest fires over the western Iberian Peninsula (Portugal and the Spanish region of Galicia). It was found that easterly circulations [east (E), northeast (NE), and hybrid anticyclonic northeast (HANE)] were associated with an increase in the number of forest fires in the domain studied. The number of forest fires per day was 549, 357, and 309 for the E, NE, and HANE, respectively, whereas the average value was 299 fires per day. It was seen that this effect is the result of the low-level heating and drying caused by easterly circulations. The possible impact of easterly circulations on the low-level wind was also analysed, although in this case the results were not clear. The indices used to classify the circulation weather types were also employed to develop a statistical model for the daily number of forest fires. Stepwise multiple regression showed that only two indices are necessary (correlation coefficient 0.5, significant at the 0.01% level): the western component of geostrophic wind and geostrophic wind intensity. Copyright (c) 2012 Royal Meteorological Society