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On the suitability of the use of normalized difference vegetation index for forest fire risk assessment

The NOAA‐AVHRR normalized difference vegetation index (NDVI) has often been used for forestry applications, including forest fire risk estimation. The decrement of NDVI values over a particular area has been considered an indicator of vegetation stress and linked to high fire risk. In the Mediterranean region, a large number of fires occurred in areas where the NDVI values were low. Consequently, the link between low NDVI values and fire occurrences was established. However, studies supporting this hypothesis were based only on analysis in areas that suffered fires and information over similar areas where fires did not occur was not considered. This study investigates the ability of NDVI to discriminate levels of fire risk in Spain using a very large dataset of satellite sensor images and fire events. The relative frequency distribution of NDVI values in both areas that suffered fires and those where fires did not occur, was compared in a 10 year period. The results highlight that NDVI values in areas where fires took place were similar to NDVI values in areas in which fire did not occur, showing the limitations of using the NDVI as an index of fire risk.