## 3 Results
### NDVI and NDWI Spectral Indices  
NDVI (Normalized Difference Vegetation Index) is a dimensionless index that defines vegetation cover through the difference between visible and near-infrared reflectance [52]. It is observed that in the western zone (Figure 5) as well as in the southern sector of the watershed, the absence of vegetation is noticeable, while in the west, there is the presence of savanna areas, characterized mainly by sparse, low vegetation, resulting in low NDVI.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Random 70** & **Forest** & **Eucalyptus** & **Exposed Soil** & **Brazilian Savannah** & **Mining** \\ \hline Forest & 1612 & 7 & 0 & 8 & 0 \\ \hline Eucalyptus & 3 & 1220 & 0 & 2 & 0 \\ \hline Exposed Soil & 0 & 0 & 1127 & 0 & 3 \\ \hline Brazilian & & & & & \\ Savannah & 8 & 0 & 0 & 437 & 1 \\ \hline Mining & 0 & 1 & 1 & 0 & 69 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Confusion matrix of the classification performed by the Random Forest model applied to the Sauipe River basin, showing excellent classification results.  
Figure 4: The result of machine learning classification, highlighting some areas of interest for Dunnian runoff. (1) Prominent presence of savanna. (2) Concentration of mining activity. (3) Concentration of the largest fragments of Atlantic Forest and intrusion of forestry. (4) River mouth, showing the complexity of spatial use with forestry, eucalyptus, and savannization.  
The southern sector is characterized by exposed soil and mining, that is, the absence of vegetation. This is prominent in the more rugged areas of the terrain (Figure 6), especially in the northern sector and at the mouth of the basin where the highest NDVI values are found. However, it is not predominantly forest but rather fragmented areas with the intrusion of forestry.  
NDWI (Figure 7) follows the trend of NDVI; in other words, this index seems to directly influence the concentration of vegetation index, a topic discussed later. The counterintuitive aspect is that higher NDWI values were expected along the banks of the main channel, which is not observed except in the middle course of the river and at its mouth. The relationship between these two spectral indices seems to indicate a'symbiotic' balance between fragments of Atlantic Forest and soil moisture. Several factors suggest this possibility: I--along the riverbanks, control of Dunnian runoff only occurs where there is vegetation; II--there is a spatial correlation between NDWI and NDVI; III--areas with savanna formation have little overlap with forested areas.  
Figure 5: NDVI in the Sauipe River basin, highlighting the low index in 1 West and 2 South, in the former primarily due to deforestation and replacement of the Atlantic Forest by savanna, and in the latter due to sand mining activities. Areas 3 (north) and 4 (river mouth) exhibit the highest indices, driven mainly by soil moisture, as we will discuss later.  
Figure 6: Hyposmetric map of the Sauipe River basin, highlighting 1 (west) and 3 (north) areas with higher elevations. Area 3 shows a greater tendency towards Dunnian runoff. In 2 (south) and 4 (mouth), elevations and slopes are lower.