# Investigating the Impact of Wildfires on Lake Water Quality Using Earth Observation Satellites
## 3 Results
### Time of Occurrence of Chl-a and Turbidity Peaks after a Fire  
When Chl-a and turbidity peaks succeeded a fire event, we were able to calculate the time (expressed in days) and concentration (mg m\({}^{-3}\)) of the peaks occurring after a fire. We calculated the first detected peak of Chl-a and turbidity occurring immediately after a fire occurrence and the maximum peak developed during the year. The median timing of the first detected post-fire Chl-a peak was 58 days (mean \(\pm\) standard deviation = 65 \(\pm\) 45 days) across all lakes investigated, and for the majority (58%) of lake-year cases the first peak of Chl-a appeared within 90 days from the fire event (Figure 6a). The median time of the maximum annual Chl-a peak that developed after a fire was 103 days (mean \(\pm\) sd = 110 \(\pm\) 72 days) across all lakes and resulted in a similar percentage of lake-year cases (7-8%) up to 150 days (Figure 6b). The median number of days for the first peak in turbidity after a fire was 68 days (mean \(\pm\) sd = 72 \(\pm\) 52 days) across all lakes, and for most lake-year cases (52%), the first peak of turbidity occurred within 75 days from the fire event (Figure 6a). The median time of the maximum annual peak of turbidity was 151 days (mean \(\pm\) sd = 163 \(\pm\) 85 days) after a fire event (Figure 6b). The two largest lakes in our dataset (Great Slave Lake in Canada and Lake Chad in Central Africa) had a relatively fast response in developing the first turbidity peak after a fire, within 70 days, and most other large lakes (lake area \(>\) 2000 km\({}^{2}\)) had a response within four months (122 days) after a fire. Figure 5: Time series data of burned area (km\({}^{2}\)), standardized precipitation index (SPI; red and light blue boxes for extremely dry and wet conditions, respectively), water temperature (LSWT; T\({}^{\circ}\)), chlorophyll-a (Chl-a; mg m\({}^{-3}\)), and turbidity (NTU) of Lake Chad (Chad/Niger) and Lake Volta (Ghana). The analysis of timing in peak development for Chl-a and turbidity identified the successive concentration peaks after a fire's occurrence and the results were used for investigating relationships with burned areas in lake catchments. Burned area parameters were calculated and considered both as a ratio of burned area over total burnable area in the catchment (ratio BA/A) and burned area over the closest burnable area to a lake (ratio BA/A level 0-4). We found that in general, lakes with a higher proportion of burned area in relation to burnable catchment area showed a faster timing for developing maximum peaks of Chl-a (Figure 7), although the noise in the data did not allow us to fit a significant trend in the relationship. The timing for development of Chl-a maximum peaks in years when lakes had an annual BA/A level 0-4 (Figure 7a) ratio > 0.25 was 90 days on average (N = 41) and in a relatively restricted time range (153 days), while when the BA/A (level 0-4) ratio was <0.25, the mean was 112 days (N = 307) in a wider time range (339 days). For the ratio BA/A (Figure 7b), the days to the Chl-a maximum peak was on average 102 days (N = 60) with ratio > 0.25, while when the BA/A ratio was <0.25 the mean was 114 days (N = 288). Patterns of the ratio BA/A with the timing of the first peaks of Chl-a and with both the first and the maximum peaks of turbidity were less distinct. In order to investigate further the influence of fire and precipitation parameters on the timing of peak development for Chl-a and turbidity, we ran a boosted regression analysis. Models produced by this regression were weak based on the high values of Root Mean Square Error (RMSE), which ranged from 48 to 63 days. Although the models should not be overinterpreted, the factors estimated to have the most influence for Chl-a and turbidity were SPI, maximum BA, lake position (latitude and longitude) and total rainfall. Results are shown in Figure S2 in the Supplementary Materials.