Elements for Life

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OREST FIRES ARE

one of the most serious natural risks

affecting Portugal, especially during the summer time.

They are dependent on many factors and produce

various effects, making them a very complex and challenging

problem. For the deflagration of a forest fire it is necessary to

have combustible substance and a source of heat. Its evolution

depends on atmospheric conditions and the state of the vege-

tation.

In countries with a Mediterranean climate, the predominant

meteorological conditions over the summer months such as

heat and dehydration of vegetation encourage the occurrence

of forest fires. Portugal has a relatively long warm and dry

season, during which wild fires can occur. In the period of the

fire season, considered to be between May and October,

Portugal suffers a large number of forest fires and burnt area.

Forest fire spread is related to social factors, often consuming

a vast forested area.

In Portugal, different institutions are directly involved in the

prevention and combat of forest fires. These include the

Portuguese Civil Protection and Fireman Service, the Forestry

Service and the Portuguese Institute of Meteorology. In recent

years, research and a successful collaboration between these

institutions has led to a better understanding of the deflagra-

tion and propagation of the forest fires and the investment of

time and resources to provide guidelines and possible solutions.

When evaluating the global risk of forest fires, it is absolutely

essential to take into consideration the impact of meteorolog-

ical conditions. The fire risk brings together detailed

information from meteorological net stations all over the world,

aiming to provide a very precise analysis of meteorological

conditions, weather forecasts and climate conditions affecting

all domestic territories.

The research from the Portuguese Institute of Meteorology

includes, beyond all the general meteorological information,

specific products, such as the Fire Weather Index (FWI) of the

Canadian System and the Combined Risk Index of Forest Fire

(ICRIF), which are all directly used to support the prevention

of forest fires. This information is made available to all national

entities that have responsibilities in the prevention and combat

of forest fires. A daily brief is established between the Weather

Forecasting Centre and the National Civil Protection and

Fireman Centre. The information is made available to the

public during the most critical parts of the year.

Fire Weather Index

The information distributed by the Portuguese Institute of

Meteorology is based on the Fire Weather Index (FWI). The

calculation of the FWI includes several meteorological vari-

ables; the temperature, the relative humidity of air, the wind

speed at surface and the amount of precipitation observed in

all the meteorological stations, taking into account the fore-

cast for the next two days.

The information also contains charts with different classes of

fire risk defined by regions. The predicted fire risk classes are

based on the FWI integrated with the country vegetation type

map from the Portuguese Forestry Service. The different classes

of Fire Risk are shown in different colours, relative to the inten-

sity of risk from yellow to red.

The Portuguese Institute of Meteorology also computes a

daily combined Forest Fire Risk Index, the ICRIF (Índice

Combinado de Risco de Incêndio Florestal). It is a dynamic

index, combining meteorological, vegetation status and struc-

tural information and computing, not just the probability of

forest fire ignition, but also the capability of fire spread.

The Portuguese Institute of

Meteorology and forest fires

Luis Pessanha, Julia Silva and Teresa Abrantes, Instituto de Meteorologia, Portugal

Forest fire risk classes by regions

Source: IM Portugal