*2.7. The Normalized Burn Ratio (NBR)*

The normalized burn ratio (NBR) and its difference were estimated and used in the GEEBAM program to find out where wildfires in NSW have affected vegetation [36]. GEEBAM used a series of Sentinel-2 images to derive NBR and its difference (dNBR) between the pre-fire and post-fire. NBR is an index designed to highlight burnt areas in large fire zones. The formula is like normalized difference vegetation index (NDVI), except that the formula combines the use of near infrared (NIR) and shortwave infrared (SWIR) wavelengths [40]:

$$NBR = \frac{(NIR - SWIR)}{(NIR + SWIR)}\tag{9}$$

A threshold of dNBR was chosen through visual interpretation to create GEEBAM classes. A higher value of dNBR indicates increased likelihood that the area has burned, while areas with negative dNBR values may indicate regrowth following a fire. GEEBAM was used during the 2019–2020 summer to rapidly predict how severely the tree canopy has burned. It was updated monthly by measuring the change in the color of vegetation after a fire based on NBR. The NBR and fire severity classes were further used in this study to assess the vegetation cover and erosion change before and after the fires.

#### *2.8. Validation of Hillslope Erosion Estimation*

The direct assessment of final erosion results was difficult as it was not possible to carry out field measurements on erosion and sediment immediately after the wildfires and storm events, especially during this Covid-19 pandemic period and the accessibility to the mountainous area. As the K-factor and LS-factor are relatively stable and they were validated in our previous studies, the cross validation in this study was focused on the cover-management and the rainfall erosivity factors (refer Equation (1)). These include: i) The cover-management factor estimated from MODIS, Sentinel-2, and Landsat-8; ii) the rainfall erosivity factor estimated from BoM gridded rainfall and radar rainfall. The Nash–Sutcliffe model efficiency coefficient (NSE) and relative error were used to assess the relative accuracy and differences [33]. In addition, normalized burn ratio (NBR) as used in GEEBAM was also used to compare FVC (used in RUSLE).

### **3. Results**
