7th Workshop on Forest Fire Management - EARSeL, European ...

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IV - BURNED LAND MAPPING, FIRE SEVERITY DETERMINATION, AND VEGETATION RECOVERY ASSESSMENT
slides and floods, and to assist burned area rehabilitation activities.
Extended post-fire monitoring of vegetation regrowth is also useful for
characterizing fuel hazard dynamics, an important contributor to wildfire
risk assessment. Previous studies have addressed various aspects of satellite
monitoring of post-fire vegetation regrowth in Mediterranean-type
ecosystems. Viedma et al. (1997) analyzed regrowth pathways and recovery
rates of different plant communities in the Mediterranean coast of Spain at
five different dates, between 1984 and 1994, using Landsat Thematic
Mapper imagery and the normalized difference vegetation index (NDVI).
Solans Vila and Barbosa (2009) compared different methods to obtain
quantitative estimates of vegetation recovery in an area burnt in Liguria
(Italy) in 1998. Bisson et al. (2008) proposed the Vegetation Resilience
after Fire (VRAF) index, to map the ability of vegetation to recover after
fire, based on composition of the vegetation community, soil type and
geology, and terrain slope and aspect. Díaz-Delgado et al. (2002) used the
NDVI from Landsat imagery to monitor vegetation recovery after successive
fires in Catalonia (NE Spain) between 1975 and 1993.
2 - Materials and methods
Our study covers the entire area of Continental Portugal (Fig. 1), which has
the highest fire incidence in Southern Europe, with a mean annual burned
area of 110,000 ha, corresponding to 1.2% of the study area. The fire season
of 2003 is the worst on record, with 430,000 ha burned, about 4 times
the mean annual value and one and a half times larger than the previous
maximum, recorded in 1985. Between 30 July and 3 August 2003, 80 fires
burned more than 220,000 hectares, coinciding with an extreme heat wave
over Europe estimated to have been a 500-yr return interval event. We used
MODIS Enhanced Vegetation Index (EVI) with 250 m spatial resolution, 16
days data from NASA MODIS/Terra product named “Vegetation Indices 16-
Day L3 Global 250m” (MOD13Q1), from 2000 to 2008, to characterize vegetation
dynamics in the burned areas, starting approximately three and a
half years prior to fire dates, and extending for over five years after the
fires. The starting data of February 2000 allows the characterization of
undisturbed vegetation dynamics in the fire-affected areas. The post-fire
length of the time-series ought to allow for substantial vegetation recovery,
up to fuel loads capable of sustaining new fires. The images were
processed with Modis Reprojection Tool (MRT)in order to mosaic and clip
the study area. Then, TiSeG (Colditz, Conrad et al., 2008) software was used
to do a quality assessment to screen out low quality data and to calculate
time-interpolated values for filling the data gaps created. Interpolation was
performed on a single pixel basis, using cubic splines. For each of three
sample fires, located respectively in NE, Central and SW Portugal, buffer
areas were defined to provide control data for monitoring fire-unaffected
vegetation dynamics. In order to extract the EVI values from each pixel a