## 3 Results
### Comparative Analyses of Soil Moisture Anomalies Versus Land Surface Temperature Anomalies
#### 3.3.4 Sensitivity Analyses of Drought-Related Fire Activity  
Landscape fires modify the physical and radiative properties of the surface [56; 57]. Fires in the Mediterranean are mainly caused by human activities related to agricultural practices. In this regard, identification of the regions most vulnerable to biomass burning is of importance regarding some prevention activities. In general, the process of diagnosing fire risk includes recognition of critical fire weather patterns. Usually, fire weather indices are considered, but this approach is useful for a quick glance across varying time periods and geographic areas to identify possible problems. However, it is  
Figure 8: Spatial distribution over Bulgaria of correlation between the monthly mean anomalies of root zone SMAI and ISASAF LST (MSG retrieval) for (**a**) the whole growing season, (**b**) May, (**c**) June, (**d**) July, (**e**) August, and (**f**) October. Anomalies are calculated for the 2007–2018 period. Mountain regions above 800 m altitude are excluded with a mask. important to understand that these criteria could be met in periods where the fuel would not support fire, or conversely, where drought conditions are so profound that an event with less significant weather could still yield a catastrophic fire situation. Therefore, non-meteorological elements can significantly contribute to the enhancement of weather impacting the fire environment such as drought (long term and/or short term), terrain, fuel conditions, and human impacts [37; 58; 59]. There are many indices reflecting different aspects of drought that are recommended by World Meteorological Organization (WMO) [60]. It is difficult to devise a universal drought index because of the spatial and temporal complexity of drought. Drought indices (standardized precipitation index, Palmer drought index, etc.) are frequently used in a local area and can quickly indicate if the landscape is receptive to fire. The use of these indirect indices results in substantial uncertainties in the resulting analyses. In particular, one of the most widely used, the Palmer drought severity index (PDSI), has been criticized as having several limitations [61; 62]. It has been noted that the PDSI may not be comparable between diverse climatological regions, e.g., [63]. An additional layer of analysis uses information on the vegetation (fuel) to indicate the potential for fire activity. The SMAI index (Section 2.2) can provide combined information for both drought and related vegetation stress as a prerequisite of fuel dryness and related fire risk. Remote sensing data are sensitive to the vegetation drought response and enhance capabilities for drought monitoring and detection. The high correlation between SMAI and LST anomalies (Figure 8d,e) reveals that LST derived from operational meteorological satellites can be used as an alternative tool to SMAI for drought and, thus, for fire risk assessment. Monthly means of LSASAF LST for August 2016 and 2017 over Bulgaria are presented in Figure 9a,b, considering that this is typically the period with highest fire activity. Capturing the spatial and temporal variability of biomass burning can be efficiently performed through observation from geostationary meteorological satellites. The active fire detection by the Meteosat FRP-PIXEL product, providing data with 15-minute repeat cycles for the region of southeastern Europe for the summer periods of 2016 and 2017 over Bulgaria are presented in Figure 9c,d. Comparing Figure 9a,b with Figure 9c,d reveals that the MSG LST product very well indicates the most sensitive areas for wildfires: a large number of detected fires in the northwestern, southwestern, and southeastern parts of Bulgaria correspond to the areas of highest LST. Figure 9a,b shows that, on average, the land surface state assessed by LST is more receptive to fire in August 2016 than in August 2017. This is reflected by the higher fire activity over Bulgaria in the summer of 2016 than in 2017, as demonstrated in Figure 9c,d.