This function calculates the Vegetation Drought Index (defined by Meteo France), as a combination of Drought Code and Duff Moisture Code
vdi(dc, dmc)is the Raster* containing the Drought Code.
is the Raster* containing the Duff Moisture Code.
The function returns a categorical Raster* object. Values and their descriptions are listed below:
1 = No fire vulnerability, corresponding to an important superficial humidification.
2 = Very limited drying. Small fires possible.
3 = The zone is considered vulnerable, due to strong wind and low humidity.
4 = Important drying; the zone is considered vulnerable. Fires can occur in any conditions, excepts by high air moisture. Very severe Fire Weather Danger by moderate wind, even low wind with foehn effect or very hot and very dry air. Strong drougth rules are applied, the FWI is no longer appropriate.
5 = Extreme drying, the zone is considered extremely vulnerable. Very big fire conditions are gathered. Permanent risk of very big fires on slope zones. Catastrophic fires are possible in any zones, by moderate or strong wind. Strong drought rules are applied, the FWI is no longer appropriate. The IPse works well and models very fast fire propagation speeds (sometimes underestimated).
The function returns a categorical Raster* object with extent,
resolution and land-sea mask matching those of dc (or dmc).
Values are integers in the range [1, 5].
if (FALSE) {
dc <- brick("dc.nc")
dmc <- brick("dmc.nc")
x <- vdi(dc, dmc)
}