the fire clouds

Huge fires produce storm clouds that shoot lightning and embers everywhere - this is not an imaginary scenario, but the reality of forest fires around the world in recent years. What is the explanation for the unique phenomenon, which is expected to increase due to climate change?

Neta Nissim, Zveta - news agency for science and the environment

The giant fire that occurred in British Columbia, Canada in August 2017 will not soon be forgotten by the residents of the area. What started as a routine forest fire, gained momentum and quickly turned into a terrifying sight: huge black clouds rose above the fire area, drawing in ash and hot coals as well as water that evaporated from nearby lakes. The clouds formed into huge columns, which began to produce lightning storms, from which more fires were ignited. About 4,700 square kilometers (square kilometers) of natural forests caught fire in that fire, and in total about 13,000 square kilometers of forests burned that summer in British Columbia (more than half the area of ​​the State of Israel).

In recent years, scientists have been following with concern an increase in the frequency of this phenomenon - natural fires in the forests, which lead to the formation of storm clouds called pyrocumulonimbus (compound of cumulonimbus - storm clouds that create thunderstorms, with the prefix "pyro" meaning fire). Apart from the fact that these clouds produce more fires, their enormous size makes them a factor that affects the environmental conditions on a huge scale: they send polluting particles many kilometers away, and can even block the sun's radiation. In a fire in Canada, smoke and ash particles were emitted into the lower stratosphere (the middle layer of the atmosphere, which is at a height of about 17-50 km above the earth's surface), which spread and reached the North Pole region.

The concerns raised by the scientists increase in the face of the predicted trend of the effects of climate change: according to estimates, in the coming decades more extreme climate events are expected (heat waves, in the forms and changes in the pattern of precipitation) that will create conditions that are suitable for the formation of fires, which may also accelerate the trend of the formation of fire clouds.

Storms with the intensity of a volcanic eruption

This is not the first major event of huge fires that cause huge storms, which cause more fires. In 2009 in southeastern Australia, the "Black Saturday" fire claimed the lives of 180 people, in what is considered one of the biggest fire disasters in the continent's history. The pyrocumulonimbus clouds that formed over the fire area sent the first lightning strikes to the ground five hours after the initial fire started. A huge wildfire on the ground consumed 1,700 km2016 of natural forest. In another event of huge wildfires that occurred in May 88,000 in Alberta, Canada, and led to the evacuation of 22 residents, lightning caused by the pyrocumulonimbus storms ignited several new forest fires XNUMX km north of east of the initial source of ignition.

"In terms of the climatic impact, the effect of pyrocumulonimbus clouds can be compared to the effect of moderate volcanic eruptions," explains Prof. Yoav Yair, dean of the School of Sustainability at the Herzliya Interdisciplinary Center, who specializes in lightning storms. "The conditions for the formation of these clouds are first of all a large forest fire as an initial condition, then deep instability in the atmosphere, and finally high humidity, which usually exists in heavily forested areas.

"The fire causes a very rapid rise of hot air, which contains huge amounts of aerosols - particles, water vapor and soot. The condensation of the water vapor and the high vertical speed causes the formation of clouds with a large vertical dimension, which can reach up to the stratosphere. These clouds excel in very high amounts of Lightnings, and there is a delay in precipitation processes, or in other words - the rain does not fall immediately, and the cloud continues to develop vertical.

"By the way, it injects huge amounts of particles, smoke, soot and water vapor into the stratosphere. These particles change the radiation balance and return more short-wave solar radiation directly into space." These gases and particles may accumulate for months in the stratosphere, when they reflect solar radiation and affect changes in global temperature for long periods, as was the case for example after the eruption of the Pinatubo volcano in 1991.

A chaotic situation that is difficult to deal with

Climate change causes large natural forest fires to occur more frequently and more intensely. The phenomenon of powerful storms created as a result of natural fires is also on the rise, and occurs in places such as Texas, Portugal, South Africa and Argentina - where they did not occur before the last few years. According to the researchers, one of the reasons for the recurrence of the phenomenon is the increase in temperature, which produces more intense fires, which in turn produce stronger storms and columns of smoke that emit more carbon and water vapor into the air and stratosphere, which also accelerate the formation of the phenomenon.

The fires created as a result of pyrocumulonimbus may change the fire management strategies that exist today, because they produce a chaotic situation that is very difficult to deal with. These storms can also reach the speed of a tornado, create vortices and "shoot" embers in all directions (in a range that can reach 3 km in some cases).

As mentioned, the full reasons for the formation of pyrocumulonimbus have been researched and tested for several years, and the physics behind the phenomenon continue to amaze meteorologists and atmospheric researchers. What is known about the phenomenon is that when very hot air from a humid environment (forest), created as a result of a fire, moves upwards, it cools quickly and produces "fire clouds" that look and behave like classic storm clouds. However, the heat and many particles in the fire smoke cause a dynamic reaction that inhibits the cloud from producing precipitation, and instead it moves and causes more high-energy fires.

"Take good care of the forests"

It is not yet known what the growth rate of the phenomenon is, but the researchers assume that the "clouds of fire" will form more frequently in the future, as the earth warms and the scope of large natural fires also increases. As of recently, researchers have documented an average of 25 such events per year only in the Western North American region.

And what is the chance that such storms will also be produced in Israel? "Currently in Israel there is only a small danger of the formation of the pyrocumulonimbus phenomenon," explains Yair. "Fortunately, the atmospheric conditions in Israel are less suitable for the occurrence of the phenomenon, because such developed clouds are formed mainly in winter - whereas fires in Israel usually occur when the weather conditions are hot and dry and less humid, and there is no deep instability necessary for the development of clouds. At the same time, there is no Rule it out completely, and we may see such clouds in extreme storms. Another thing is that we don't have forested areas of the same size as in Canada or Alaska, or words Otherwise, the amount of 'fuel' that will create the clouds is relatively small."

Either way, there are steps you can take today to prevent damage from massive wildfires. "Forests have an important global impact on our existence, this is because they remove carbon dioxide from the atmosphere and fix it in the biosphere, thus contributing to slowing down global warming," says Yair. "What we can do in order to deal with the recurrence of the phenomenon on a global level is to take good care of the forests so that their sensitivity to lightning strikes is reduced. The right actions begin with the removal of dry cuttings in large areas of forest, and continue with proper forest management, monitoring the more dangerous areas where the recurrence of the phenomenon is possible, and preparing in advance of a scenario where a fire that develops in one area will move or 'jump' to another forested area."