Inter-relações fogo – vegetação – atmosfera: entender os processos para prever os regimes de fogos rurais em Portugal (FLAIR)
According to the official data provided by the National Forest Authority (Autoridade Florestal Nacional, AFN), during 1980-2006 over 3 million hectares (equivalent to almost 3/5 of the forested surface) have burned in Portugal, of which the impressive amount of 920 thousand hectares (about 10% of the territory) concentrates in the 3-year period of 2003-2005 [PER06, CAL08].
Wildfires in Portugal affect a variety of vegetation types and have dramatic impacts at the ecological and economical levels. For instance, fires are the major limiting factor of forest as an economic activity. The majority of fire events are human caused (both negligence and arson) and have intricate effects on vegetation due to the complexity of landscape structures and because of the distinct responses of vegetation to the different fire regimes [NUN05].
The time series of burned area presents a highly inter-annual variability, ranging from values as low as 22 (30) thousand hectares in 1988 (1997) up to the outstanding amounts of 420 (330) thousand hectares in 2003 (2005). The large spatial and temporal variability is generally associated to natural conditions, e.g. the morphology of the landscape, the land cover and the vegetation as well as to meteorological factors that have a determinant role in fire behaviour, especially in the case of large wildfires [PEM05].
There is also a long-term increase in both the extent and severity of wildfires which is generally attributed to the demographic and socio-economic changes that took place in the rural areas of the country and have affected land use and land cover, as well as to climate change that has increased the likelihood of occurrence of weather patterns favouring the onset and spread of wildfires [TRI06].
Considerable effort has been spent in the last years to better understand the regime of wildfires in Portugal. Special attention has been naturally devoted to the ways land and atmosphere affect wildfire activity and the question about which of the two factors plays the main role is still a matter of debate. On the one hand, fire regimes depend on the type of land-use and land-cover, some of them leading to preferential spatial patterns of fire occurrence; fire events may in turn lead to reduced vegetation growth and to a decrease of fire events. On the other hand, temperature and precipitation regimes during the spring that precedes the fire season may induce stress conditions in vegetation cover [GOU09] making it prone to burn, especially if, during the fire season, there is the establishment of atmospheric circulation patterns which induce extremely hot and dry spells over western Iberia (even of shortduration) that favour the ignition and spreading of fires [DAC07].
Disentangling the roles of land and atmosphere is a very complex task and it is likely that the relative importance of these two factors depends on the temporal and/or spatial scales adopted when analyzing the fire regimes. Climate and associated weather patterns, namely extreme events, affects fire ignition; climate also affects vegetation stress [GOU08, LIB06] which in turn is related to the type of fire regime. Vegetation recovery affects fire regimes and is also conditioned by weather events [PEJ08] that in turn determine climate. Fire regimes appear therefore as resulting from a number of interacting factors, with spatio-temporal scales of their own. Interacting factors also evolve in time because of changes in both land cover and climate.
Fire regimes have to be analysed in a synergic way, by looking at fire, land and atmosphere as an integrated system. This is the novelty of the present project since to our knowledge no attempt has been made to undertake a systematic study of this type in Portugal. In order to properly achieve this goal, the Project relies on Research Teams that have been working together on the subjects of fire, vegetation and atmosphere in the last 15 years [PEJ94, DAC98].
First, the major characteristics of fire will be assessed based on statistics of active fires and fire scars as derived from a variety of datasets relying on both in situ observations and satellite imagery. A variety of meteorological data (observations, analyses and climate scenarios) will then be used to uncover relationships between weather conditions and fire regimes as well as to assess the impact of meteorological factors on vegetation stress (recovery) prior to (after) fire events. Finally an integrated analysis will be undertaken based on present climate scenarios, which will be used to anticipate fire regimes for a variety of scenarios of climate change.
Wildfire activity in Portugal has turned into a very serious problem that is likely to develop into an even more serious one in the decades to come. Results from such an integrated project would be an invaluable guidance to firemen, forest managers, policy makers, researchers and to those having to deal with the problem of forest fires in Portugal.
Fundação da Faculdade de Ciências (FFC/FC/UL)