Assessment of fuel dryness index on mediterranean vegetation

Assessment of fire potential at any scale requires advanced or integrated indices that include long-term and short-term variables to produce the potential fire environment. Well-known integrated indices are the Canadian Forest Fire Weather Index (FWI) used in Canada, Italy and New Zealand, the McArthur Fire Danger (Meter) Index (FDI), and the remote sensing based Fire Potential Index (FPI) in that it combines various factors into a single index. They differ from the U.S. National Fire Danger Rating System (NFDRS), which uses three indexes: (1) Occurrence, (2) Burning and (3) Fire Load, which are based on three components: (1) Spread, (2) Energy Release and (3) Ignition to characterize fire danger. All systems include sub-models for estimating fine fuel availability and fine fuel moisture, such as the 1-hour time lag fuel moisture and the Keetch-Byram Drought Index (KBDI) of the NFDRS, the fine fuel moisture and duff code of the Canadian FWI, and the drought factor and the fuel moisture model of the FDI . A simple, relatively low cost method to remotely obtain a fuel dryness index was recently developed to evaluate the influence of fuel dryness on fire potential. The fire dryness index (Fd) is based on the surface energy balance, where available energy (Rn - G) is partitioned into sensible and latent heat exchanges (H + LE). Clearly, any method to measure or accurately estimate Rn, G and LE can be used to calculate Fd. In this paper, the surface renewal (SR) method for estimating H from surfaces in conjunction with Rn and G estimates provides a simple and robust method to estimate LE. Long term micrometeorological measurements were taken to test the use of the SR method to measure the fuel dryness index (Fd) on Mediterranean vegetation in two sites located in Sardinia, Italy during 2003-2005 period. Comparisons between Fd and the KBDI drought index, two modified versions of the drought factor in the McArthur forest fire danger meter, and stick test measurements were presented. In addition, a modified version of the KBDI, with the reference evapotranspiration (ETo) from the Hargreaves and Samani equation was computed and compared with the Fd calculations. Based on the results, estimating H, using the SR method in combination with Rn and G data, provides a low-cost method to calculate LE and Fd as an indicator of surface fuel and surface fuel dryness.