In the early hours of the 18th May 2020 a wildfire broke out at Wareham Forest in Dorset, South West England. The forest is an area consisting of open heathland and woodland dominated largely by Corsican and Scots Pine, with around a third of the 1542 hectares designated as a Site of Special Scientific Interest (SSSI). The blaze lasted close to two weeks and damaged approximately 220 hectares of land, requiring the assistance of over 150 firefighters before the fire was extinguished, gaining the interest of national news (e.g. BBC, The Metro).
Since the fire, the Exeter team has visited the site on several occasions in order to build a picture of what went on by using post-fire forensic approaches. Through using identifiers such as bark char patterns, needle freeze and Fern bends together with analysing charcoal reflectance, the team have been compiling a dataset of wind direction, fire direction and fire intensity at different locations through the forest. Fire severity and regrowth over time has also been monitored throughout the visits. Preliminary plots of the dataset agree with what was observed at the time of the fire and offers an opportunity to develop a nice case study of wildfires in the UK.
Alongside other the other work packages in the UKFDRS project the data from the Wareham Forest fire provides a study of fire behaviour for key fuel types and an understanding of site-level fuel structure. This information will be used to help construct fuel models and to evaluate the predictive capability of fire behaviour models ultimately help towards building a UK Fire Danger Rating System.
Many thanks to Gail for this write up of this image acquisition
On Friday 7 August 2020 a wildfire began to burn on Chobham Common an area of heathland in Surrey. The wildfire required multiple fire crews to fight the flames and the incident halted the Rose Ladies Series Grand Final at Wentworth Golf Club (BBC News, 2020). The wildfire continued to burn and then smoulder for the next four days until it was announced on 11 August 2020 that the fire was “under control” with the incident officially closed on 17 August 2020 (SurreyLive, 2020).
Sourcing Sentinel 2 pre-fire image
The Copernicus Sentinel-2 satellite data provided an excellent insight into the amount of heathland burned during the Chobham Common wildfire. The last pre-fire cloud free Sentinel-2 image was acquired 30 July 2020 at 11:06am (Figure 1A) and shows the undisturbed heathland vegetation north of the M3. There was other Sentinel-2 data acquired on 04 August 2020 and 06 August 2020 but unfortunately the Chobham Common area was not visible due to cloud cover. Sentinel-2A and -2B data consist of 13 spectral bands. Figure 1A shows 30 July true colour composite which uses spectral bands 4 (red), 3 (green) and 2 (blue) to create a pre-fire image.
Burned area images during the wildfire event
Figure 1B shows the first Sentinel-2 true colour image during the wildfire acquired 9 August 2020 at 11:06am (2 days into the wildfire event). The burnt area can be clearly seen with the black to dark grey tones and the burn scar perimeter has been digitised to provide a quantification of total area burned at ~69 hectares.
A false colour composite was also produced using spectral bands 8 (near infrared), 4 (red), 3 (green) assigned to the red, green and blue colour channels (Figure 2). The burn scar area can clearly be delineated in dark grey tones from the surrounding healthy vegetation visualised in red tones. Healthy vegetation reflects near infrared radiation which in this colour composite has been assigned to the red channel. Whereas the red and green wavelengths (bands 4 and 3) assigned to the green and blue channels are absorbed by healthy vegetation as part of the photosynthesis process. The buildings in the landscape are depicted in cyan blue tones and show how close they are relative to the burned area.
The wildfire was under control on the 11 August and ideally Sentinel-2 data covering Chobham Common on that day would have been very useful to compare with the 9 August image. Unfortunately the swath of the 11 August 2020 13:41 Sentinel-2A image acquisition just missed the Chobham Common area and image acquisitions thereafter on 14 and 16 August 2020 have been covered by cloud. A Landsat 8 image acquired on 12 August 2020 shows no change in burned area extent since the Sentinel-2 9 August image. Therefore, the 69 hectares measured on 9 August 2020 looks to be a good overall quantification of burned area for this incident. It is worth noting this figure is 133 hectares lower than the estimated area burned of 202 hectares (500 acres) headlined on 17 August 2020 when the incident was closed (SurreyLive, 2020).