Conclusions
The influence of sub-tropical anticyclones on the climate of Madeira sometimes gives rise to a pattern of circulation in which the warm and dry air from north-west Africa reaches the Madeiran archipelago. When this occurs in summer and/or in periods of drought, the risk of wildfires rises and, as Madeira is a small and mountainous island, fire fighting becomes difficult and dangerous.
In early August 2016, a series of wildfires occurred on Madeira Island during a period of extremely high temperatures, with drought as a background state. The driver of these wildfires, which became a true fire disaster, was a foehn event.
There are 4 possible mechanisms for foehn warming and drying, while foehn air can be the result of more than one mechanism at the same time. In the present case the most probable dominant mechanism was the isentropic drawdown. In this mechanism the foehn air comes from higher levels (upwind of the mountain barrier) as the low-level flow is blocked by the mountain. The upwind flow can already be warm and dry and the low-level flow is cool and moist. The flow from higher levels is then advected isentropically down the lee slopes.
The observations from weather stations verified the existence of the foehn event and the numerical model allowed identifying the orographically forced flow dynamics. In addition, the new ASCAT product was tested, with a 6.25x6.25 resolution. With the available data it was possible to identify the low-level air being blocked on the upwind side of the mountain barrier.
The remote sensing products from the LSA SAF, MODIS and VIIRS, with the identification of the fires, their severity and the burned area made it possible to relate them to the foehn event.