After two weeks of dry and very hot weather in parts of the Mediterranean, several countries have been impacted by devastating wildfires.
27 July 2023
27 July 2023
By Djordje Gencic, Ivan Smiljanic, HansPeter Roesli and Jochen Kerkmann
A massive and stagnant dome of very warm and dry air dominated the weather from 10 July, across parts of southeastern Europe and much of the Mediterranean, caused by a seasonal strengthening of the ridge of the Azorean high pressure system (Figure 1).
However, this year's case is extreme due to the absence of weather systems that would, at least for a brief period of time, break that dominance by pushing cold fronts through the region, bringing some relief. Very dry, hot, and occasionally windy conditions, prevailed over the course of two weeks and caused a very high risk of wildfires in many areas in Mediterranean.
Devastating fires impacted islands of Rhodes, Corfu, as well across mainland in Attica and Peloponnese.
The first large fire in the period in Greece, was in western Attica peninsula on 19 July, which was quickly extinguished, but managed to burn a considerably large area due to conditions being very conducive. Figure 2 is the Sentinel-2 L2A True Colour RGB, which shows a huge contrast between green and burnt vegetation, plus smoke from the active fires.
The most fierce wildfire was in Rhodes where almost 15 percent of the island had been burnt by 26 July. Rhodes lies in the part of the Aegean Sea heavily affected by the seasonal northerly wind circulation related to strong overheating of the Asia minor and Middle East — wind is one of the main contributors to the spreading of wildfires. This can be seen in the Meteosat-11 Natural Colour RGB with wind barbs overlaid (Figure 3).
Here one can see a pattern typical for summer months — wind from northern quadrants. Additionally, due to the sensitivity of VIS0.6µm (blue component of the RGB), a smoke plume appears in light blue, especially visible over the sea.
Massive fire in Rhodes can be seen in IR3.9µm loop (Figure 4). Fires are seen as hot spots in the imagery and in greyscale view they appear completely black. Saturation of the IR3.9 happens at 336K and fires above that temperature typically show as an artefact in shape of concentric circles, as it can be particularly seen on 22 July when this pattern covers much of the island, reflecting the strength of the fire.
Fires and smoke are particularly visible during the day, and in composites that use the visible part of the spectrum. One of the ways to ensure a 24 hour view of the fires, is to use the Night Microphysics RGB, which features the crucial IR3.9µm channel. Although primarily used for fog/low cloud detection, it also can be used for tracking fires, as it can be seen in Figure 5.
Figure 6 shows a loop of three individual Sentinel-3 SLSTR scans of Rhodes, during the most intensive phase of the fire (22-24 July).
The Natural Colour RGB detects the smoke thanks to VIS0.6µm, and also shows the active fires in the area that already had been burnt. Active fire appears as red/bright red, due to the dominant signal in red component (NIR1.6µm) ,while the burnt area (also called 'burn scar') shows as different shades of brown. This brown colour comes primarily from the absence of chlorophyll (all vegetation burned), which strongly influences the green component of the RGB (VIS0.8µm). In this case the area is still quite hot, and, therefore, this colour comes from a moderate red and decreased green contribution (compared to area with vegetation).
The Natural Colour RGB from Sentinel-2 L2A (Figure 7), zooms in on a scene of fire in Rhodes, where unburnt vegetation shows as green and burnt in brown, active fires in bright red, and, finally, thanks to VIS0.6µm component smoke as a light blue, almost transparent, veil above the area.
Figure 8 shows experimental 2.5min FCI rapid scan commissioning data for southern Greece, in the form of the True Colour RGB combined with signal from 3.8 and 2.2 micron channels, in the regions with fires. It highlights the improvement in temporal (2.5 min), spatial (0.5-2km), and spectral resolution (presence of 0.4 and 0.5µm channels), to the previous generation of GEO satellites. Active fires show bright red-yellow-white, and smoke in brown or grey.
On the Mediterranean coast of Algeria on 24 July, there was an outbreak of strong wildfires, under the aforementioned weather conditions. In the colour enhanced IR3.9µm loop for 24 July (Figure 9), shows the fires as hot spots appearing in many places over the course of the day.
Figure 10 is the Natural Colour RGB loop for the same period.
At approximately same time, there was an outbreak of fires across Sicily, following two weeks of dry and hot weather. In the Meteosat-10 Enhanced IR3.9µm loop (Figure 11), the highest temperatures are coloured in yellow and red, indicating the fire tempearture. One can see that fires were increasing in number on 24 July and, especially, on 25 July, affecting significant parts of the region.
Our deepest sympathies are with those impacted by these events.