Forest fires effects on the atmosphere: 20 years of research in Portugal

Abstract

The aim of this study was to map the burned areas of the Selva El Ocote Biosphere Reserve for the period 1998– 2012, using Landsat TM/ETM+ images. The method was based on a visual comparison of false color images and the pre/post-fire spectral indices Normalized Burn Ratio (NBR) and Normalized Difference Vegetation Index (NDVI); it used official records of wildfires from the National Commission for Natural Protected Areas and National Forestry Commission, and hotspots identified by the National Commission for Knowledge and Use of Biodiversity and the Fire Information for Resource Management System. Landsat images were downloaded during the fire season, January–June, for each year. According to the results, 54,756 ha were affected by 1095 fires during 1998–2012. We estimated that 352 of them involved tropical forest and 743 pasture, savannah and secondary tropical forest. The catastrophic years were associated with El Niño events 1998 (42,240 ha), 2003 (1,643 ha) and 2005 (1,248 ha), suggesting that the meteorological conditions contributed to the vulnerability of vegetation to fire. These results illustrate a method for analysing the pattern of spatial and temporal distribution of burned areas and for identifying zones that merit priority attention with regard to agricultural burning and wildfires. Keywords: