What is fire time? Definition and monitoring

Sometimes, by a windy but otherwise pleasant day, a weather alert will appear on your mobile phone or your television. No, this is not an error; This is probably a notification for fires – conditions of joy favorable to the ignition and spread of forest fires.

The fire time can occur in any season, but peaks at the end of the summer and falling when the drier air and dry fuels (fallen leaves and sleeping trees) are common. Although the fire time is experienced worldwide, it has a greater risk for places like the western United States, Australia, Africa and Amazon, which are subject to forest fires.

Conditions that cause fire time

To burn, the fire needs three ingredients: heat, oxygen and dry fuel source. The following weather conditions conspire to provide them and spell the danger of shots because of this.

High air temperatures

Very hot temperatures increase evaporation, which in turn strips the humidity of easily combustible materials, including herbs, shrubs, trees, dead leaves and pine needles that act like forest fires. The fuels heated by the sun is also faster, as less thermal energy is necessary to bring them to their ignition temperature.

Low precipitation

Precipitation reduces the surface of fuel to the point that fire cannot ignite. A lack of rain or snow, or in extreme cases, a drought, does exactly the opposite; It dries fuels, allowing them to more easily combust.

Low soil humidity

The moisture of the soil (the amount of water contained by the soil) is a good indicator of “the humidity of the fuel” or how full the living plants are. When soil humidity is low, local vegetation is probably dry and stressed with water, which also means that it is more likely to burn. According to a study connecting soil to the size of forest fires in the large southern plains, soil humidity plays such a full role in the activity of the fire that it takes it from the contributions of hot temperatures and low precipitation.

Low relative humidity

When the relative humidity (a measure of the amount of water vapor is in the air) is low, it helps to dry fuels, making them more flammable.

Winds in mind

If a fire lights up, the winds can worsen it in several ways. On the one hand, they provide fire with more oxygen, which burns it faster. The violent winds also reduce the humidity of the fuel by increasing evaporation, as well as encouraging a fire to spread by pushing it physically and transporting embers before his inflamed forehead.

If you look at the weather card, look for a low humidity and strong winds and in gusts to move after the passage of a dry cold front (a cold front associated with a dry air mass). The critical fire time is also generally linked to high pressure in the upper levels of the atmosphere, because these weather characteristics can act like “heat domes”, bringing a clear sky, flowing air, very dry air and temperatures above the average during the hottest months of the year, of course.

Fire time watches and warnings

Because fire control is so strongly based on the weather, the NOAA National Service (NWS) of the NOAA works in tandem with land management organizations to monitor the problematic weather conditions. When several time of fire conditions occur simultaneously and coincide with dry fuels, the NWS will emit a fire time watch or a red flag warning.

Weather watch

A fire time watch is issued when the criteria of the red flag could be met in the near future, generally within 24 to 72 hours.

Watches give the public and firefighters time to prepare for a high risk of fire.

Red flag criteria

The criteria of the red flag are the values ​​of wind and threshold humidity which report an increased risk of fire danger. The criteria are set by the local offices of the NWS and vary from one region to another, depending on the type of local vegetation, topography, drought conditions, etc. At least, the criteria include::

• Winds of 15 miles per hour or more (measured at a height of 20 feet above the ground).
• Minimum relative humidity (usually occurred in the afternoon) less than 25%.
• A 10 -hour fuel humidity (a measure of the amount of water maintained by the grass and the leaves that take 10 hours to respond to humidity / drought changes) from 10% or less.

Red flag warning

If a red flag warning is issued, this means that the criteria of the red flag are already met or will be satisfied shortly, generally within the next 12 to 24 hours.

Expect fires that come on quickly and become difficult to control or delete. In the warnings of the red flag, burning prohibitions will also be in force.

How climate change has an impact

If you seem to see more red flag warnings today than over the past years, blame climate change. Global warming is actually increasing the duration of the fire season, or the number of days each year when atmospheric conditions are ripe for the danger of fires. A study in Nature communications reveals that between 1979 and 2013, the seasons of fire time lengthened on average by 19% in a quarter of the vegetated areas of the earth. Zoom in on the forests in the western United States, and you will find that the time seasons have been extended by eight days.

This same study also examined the time seasons longer than normal. He found that these also became more frequent due to climate change – 53% more frequent, worldwide.

Research on California reveals that, since the 1980s, the increase in state temperature of the state and the decrease in precipitation represents a 20% increase in fire indices. If recent trends are continuing, California could see a 25% increase in its fall days to 2100.