Analysis of NOAA-AVHRR NDVI inter-annual variability for forest fire risk estimation

摘要

The values of the normalized difference vegetation index (NDVI) extracted from satellite sensor data acquired by the National Oceanic & Atmospheric Administration - Advanced Very High Resolution Radiometer (NOAA-AVHRR) have often been used for estimating forest fire risk. These estimates were mainly based on the decrease in the NDVI values during the summer period. However, this decrease may be a normal phenological response of the vegetation to the summer drought in Mediterranean regions. The present work, instead, considers the inter-annual variability of the vegetation status to determine vegetation water stress. The water stress is determined by comparing the actual vegetation status, as derived from the NDVI, with its normal evolution. Thus, a novel methodology for the assessment of fire risk based on this inter-annual comparison is presented. The level of fire risk is derived from a new index referred to as the dynamic relative greenness index (DRGI). It was computed over the European Union countries and tested in Spain, France and Italy. DRGI values and the number of fires were fitted using an exponential model. The testing of the DRGI over a 13-year period showed very high correlation (R~2 = 0.94) between the number of fire outbreaks and the level of fire risk determined by the index.