# Investigating the Impact of Wildfires on Lake Water Quality Using Earth Observation Satellites
## 3 Results  
### Selection of Lakes by SPR Approach  
A hierarchical cluster analysis (Sorensen distance) was performed using the FireCCI product to identify and group comparable types of wildfires based on the land cover type burned. Based on the minimization of the indicator \(p\)-value (=0.010), the resulting dendrogram was divided into six groups. These groups showed that half of the clusters, i.e., clusters 1, 2, and 3, represented a total of 1578 lakes (78% of the 2024 lakes in the dataset) and had few records of burned areas, while the remaining clusters 4, 5, and 6 were characterized by the more consistent occurrence of wildfires (446 lakes, or 22% of the dataset). Regarding the vegetation types and the regions identified as subject to burning, Cluster 4 consisted of burned evergreen coniferous forestry in North America and Canada, Cluster 5 featured crops or natural shrubbery in America, Eurasia, and Australia, and Cluster 6 was more diversified and included the most burned areas of deciduous broad leaves, which are common in the southern hemisphere, especially in Africa (Table 1 clusters 1-6 in rows). Figure 1 shows the map of the six vegetation clusters. To support this analysis, a second cluster analysis on the total burned area for an extended period (2001-2020) was performed identifying five end groups. Two clusters, cluster I and II, contained 1394 lakes (69% of the total lakes) that had few records of burned areas, while the remaining clusters II, IV, and V were characterized by a higher frequency of wildfires and larger burned areas (630 lakes, 31%) (Table 1, clusters I-V in columns). In particular, Cluster IV was characterized by hydrological areas where a high proportion was burned every year, frequently more than 3-4% of the catchment area, and similarly Cluster III identified hydrological basins with frequent fires (annual) but only in 0.1-0.2% of the catchment area, while Cluster V had limited fire peaks and burned areas. We derived a contingency matrix by joining the results of the two clustering analysis, thereby identifying agreement on lakes where major wildfires occurred for the different land cover types (bold numbers in Table 1). From this table, we selected these candidate lakes covering a range of different land cover types and with different fire regimes (fire frequency and intensity), excluding lakes in catchments with small (low BA) and rare fires. As a result, a total of 314 lakes were therefore selected for further investigation. Because we are focusing on the terrestrial pathway of burned materials transported to lakes, the previous analysis on vegetation and fire intensity and frequency provides an indication of changes in hydrological pathways as a result of vegetation loss. Catchments that experience significantly seasonal or variable rainfall leading to overland flow may be \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{2}{*}{**Vegetation Type and Distribution**} & \multirow{2}{*}{**Rare Fires and Low BA**} & \multirow{2}{*}{**Rare Fires and Very Low BA**} & \multirow{2}{*}{**Limited Regular Annual Fires and Medium BA**} & \multirow{2}{*}{**Significant Regular Annual Fires and Medium BA**} & \multirow{2}{*}{**Limited Fire Peak and Medium BA**} & \multirow{2}{*}{**Total**} \\  & & & & & & & \\ \hline Cluster & I & II & III & IV & V & \\ \hline
**Needleleaf deciduous (Global)** & 1 & 383 & 698 & 128 & 15 & 57 & _1281_ \\ \hline
**Needleleaf, evergreen (Northern temperate)** & 2 & 43 & 48 & 14 & 0 & 40 & 145 \\ \hline
**Crops/Herbaceous (Global)** & 3 & 71 & 19 & 53 & 6 & 3 & _152_ \\ \hline
**Boreal forest (Canada)** & 4 & 54 & 10 & **13** & 0 & **18** & _95_ \\ \hline
**Crops–natural shrubber (Eurasia)** & 5 & 51 & 0 & **114** & **13** & **2** & _180_ \\ \hline
**Deciduous broad leaves (Africa, India, South America)** & 6 & 17 & 0 & **93** & **61** & 0 & 171 \\ \hline  & _Total_ & 619 & 775 & 415 & 95 & _120_ & _2024_ \\ \hline \hline \end{tabular}
\end{table}