Comparison of burnt area estimates derived from satellite products and national statistics in Europe

Abstract

Burnt area maps based on satellite observations are frequently used in calculations related to fire regime, such as those of carbon dioxide emissions. Nevertheless, burnt area estimates between products vary widely, and validation against independent data is scarce, especially for Europe. Here we compare two active fire maps (the ATSR World Fire Atlas and the Moderate Resolution Imaging Spectroradiometer (MODIS) Active Fire Product) and two fire scars maps (the L3JRC and the MODIS Burned Area Product) to independent national statistics taken from 22 European countries between 1997 and 2008. We also tested the coincidence between satellite products derived by calculation of the fraction of active fires that were confirmed by a subsequent drop in reflectance. As a large proportion of fire pixels (between 40% and 66%, depending on the product) is located on urban land or crop fields, filtering out fires located on these land uses greatly improves the agreement between satellite-based burnt area estimates and national statistics and it also improves the coincidence between satellite products. The MODIS Active Fire Product appears to be most suitable for use as a proxy for burnt area patterns, showing a high correlation to national statistics (R2 = 0.9), relatively low spatial and temporal heterogeneity and only a slight underestimation of the total burnt area (19 000 ha year–1). Unfiltered products show cases of substantial wildfire overestimation in all products, mainly attributable to anthropogenic activity, in the case of active fire products, and drought-induced vegetation dieback, in that of fire scar maps. Thus, filtering out fires on anthropogenic land uses seems to be essential when analysing patterns of forest fires from satellite observations. However, if agricultural fires are to be included, a combination of MODIS Active Fire and MODIS Burned Area products is recommended. We obtained that such combination shows low temporal and spatial heterogeneity and the highest coincidence between satellite products (25%), although the correlation to national statistics is not very high (R2 = 0.67) and clearly underestimates the total burnt area (187 000 ha year–1).