Geoscience Reference
In-Depth Information
The data produced that was used to constitute the series of regressions, was
generated by automated stations that were initially financed by the Departmental
Council of the Alpes-Maritimes. Twenty-three of these stations were selected and
provided information relating to temperature, humidity, wind, and precipitation. The
exact locations of the stations were known; therefore, it is possible to work out the
exact geographical variables for each site (Figure 8.7).
8.3.2.2.
The meteorological risk index “Carrega I85/90”
In this section we have decided to focus on the risk index that was first
developed in 1985 and then modified in 1990 so that a scale ranging from 0-20
could be allocated to a specific risk [CAR 91]. Despite its simplicity, this index was
recognized for its reliability and high-quality output and was partially used as the
source for the Météo-France index (DK), developed by Drouet and Carrega at the
end of the 1980s. The 1985 index, which was subsequently updated in 1990, was
also used by firefighters and forest workers who worked in the Alpes-Maritimes
area for more than 10 years as part of the system known as “Expert-graph”, which
was developed by the École des Mines in Paris [WYB 91]. The École des Mines is a
prestigious French engineering school in Paris that has a campus based at Sophia
Antipolis in Nice, which focuses on risk analysis.
The index's formula is written as follows:
I85/90 = (500 - (R
0.5
* H / V)) / 25
where:
- R is the soil's water reserve, which is calculated by using a simplified Penman
or Thornthwaite water budget. The aim of using such a water budget is to make the
level of water present in the soil's water reserve similar to the level of water found
in living plants (regional maximum level is fixed at 150 mm);
- H is the relative humidity;
- V is wind speed.
The value of the index varies from 0 to 20 (where a value of 20 represents
maximum danger). The index values are divided into four main groups that are as
follows: 0 to 8 represents no risk or a weak risk, 8-14 is used to represent an average
risk, 14-18 is used to represent a severe risk, and 18-20 is used to represent a very
severe risk. A value of 19 or greater is exceptional.
8.3.2.3.
An important methodological choice needs to be made: do we recreate the
different components of the index, or do we recreate the index itself?
The geographical information available, which has been measured by a GIS, can
be used in two ways to create a map that represents the meteorological risk index
[CAR 07]:
