## 5 Discussion
### Relationship Between Fires and SPEI  
The inter-relationship between fires and climate has always been a subject of paramount importance in the scientific context devoted to fires. While fires undoubtedly affect climate change, climatic factors, like rainfall and temperature, not only directly impact the probability of fires but can also indirectly alter vegetation productivity (i.e., fuel abundance), consequently affecting the intensity of fires [53; 54; 55]. In regions abundant with biomass, the primary factors driving wildfire activity are typically high temperatures and seasonal drought conditions [56; 57]. Extreme and prolonged droughts, induced by abnormal fluctuations in the climate system like El Nino, have consistently served as significant catalysts for regional fires [54; 58]. On a global scale, greater seasonal variation with sum  
Figure 12: Monthly average number of fires (**a**) and total burned area (**b**). mer and autumn being the seasons with the most frequent fire occurrence worldwide was found by using satellite data and investigating the spatial distribution, intensity, emission changes, and meteorological differences between fires in different fire-active and fire-prone regions [59]. The SPEI is a well-known drought driver and its link with fires was demonstrated in several studies. For instance, it was statistically shown that same-summer-drought conditions play a dominant role for fires in Mediterranean Europe [26]; in particular, the correlation between burned area and coincident SPEI3 (i.e., calculated for an accumulation period \(T_{a}\) = 3 months) for July and August (when usually the temperature reaches its highest value) is large in all the Mediterranean ecosystems that are characterized by a relatively high abundance of fine fuels able to dry out quickly during a single summer [32]. A correlation analysis between the SPEI (decomposed in trend and season through the LOESS method [60]) and fires in inland areas of Spain showed that short-term droughts (SPEI3 and SPEI6) have a more significant impact on fire occurrence than prolonged droughts (SPEI12 and SPEI24), while the seasonal cycles of burned area seem to be strongly associated to SPEI24, thus with prolonged dry conditions [61]  
The monthly fire counts in the Basilicata region, investigated in the present study, exhibit cycles that show significant correlations (with a \(p\)-value less than 0.05) with SPEI at specific accumulation periods (Table 2). Specifically, short-term cycles (4 and 6 months) governing the first IMF are negatively correlated with SPEI1, representing the one-month accumulation period of drought. The second IMF, reflecting the annual cycle, shows a significant negative correlation with SPEI3. Additionally, SPEI10, with a longer accumulation period (10 months), is strongly negatively correlated with the fifth IMF, which is dominated by the 5-year cycle. Conversely, the 4-5 year long cycle, modulating the fourth IMF, exhibits a good positive correlation with a long accumulation period, SPEI30. Similarly, the long-term IMFs (IMF6 and IMF7) are positively correlated with SPEI36 and SPEI48 that are characterized by the longest accumulation time \(T_{a}\). Likewise, the monthly total burned area displays correlations with SPEI at nearly identical accumulation periods (Table 3). The first IMF, governed by the 4 and 6 month periodicities, shows a negative correlation with SPEI2. Similarly, the annual cycle is negatively correlated with SPEI2. The interannual cycle (\(\approx\)5 years) governing the fifth IMF's time variation is strongly correlated with SPEI13. Furthermore, IMF6 and IMF7, characterized by fluctuations dominated by the 20 year cycle, exhibit a positive correlation with SPEI43 and SPEI48, similarly to the monthly number of fires. Figure 13 shows the relationship between cycles in fires (monthly number and total burned area) and accumulation periods of the SPEI; such a relationship suggests that the larger the periodicity in fires, the longer the accumulation period of the SPEI.