Concern about forest fires has been on the rise lately. It stands to reason that fire enhances global warming by destroying forests, since plants absorb greenhouse gases, while flames emit them.

Greenpeace has estimated that the volume of forest fire emissions is considerable, since it represents a quarter of that caused by the use of fossil fuels. However, there are difficulties in measuring this magnitude because some of the countries with the most fires – Brazil, Russia, Indonesia and several regions of Central Africa – do not have very reliable resources to make such measurements.

Other consequences of forest fires includes human fatalities, biodiversity loss, economic damage to the owners of burned areas, and the economic cost of putting them out, among others. On the other hand, the causes and prevention of fires are more complex and difficult to understand.

In Spain there are thousands of fires a year, but more than half of them are usually put down before they spread at all. Thus, the problem is not the number of fires, but the extreme virulence of a few: the so-called sixth-generation fires, which are those that burn the bulk of the hectares affected per year.

National Geographic points at three main factors that affect the spread of these macro fires: ignitions, the proximity and abundance of forests and drought. Of these three, only ignitions are the true causal factor, while the other two are aggravating factors, which can turn a modest fire into a catastrophic one, if both exceed a certain threshold.

The two aggravating factors work as communicating vessels: the drier a region is, the less forest it has. In this case, it seems that the most relevant factor is the abundance of forests. Disregarding the drought factor, however, would imply a lesser influence of climate change, a phenomenon related to increased drought, on the spread of fires.

In the Iberian Peninsula, the area of greatest fire risk is the northwest, which includes the coastal regions from San Sebastian to Lisbon, as well as Zamora, Leon and Orense. Almost two thirds of the fires occur in this region. These figures might seem striking, since the North of Spain hast the coldest and wettest weather in the country. It is precisely because of this humid climate, that the region has a lot of forests and is therefore an easy victim to forest fires.

Heat waves and human cause

According to National Geographic, when a region with a high mass of flora is affected by drought, there is a higher risk for macro fires. This is when heat waves come into play. If we look at the two worst years of the past decade in terms of fires, 2012 and 2017, there were heat waves when the most virulent fires occurred.

According to the Ministry of Agriculture and Fisheries, 96% of the fires are caused by human intervention, either through negligence or intentionally. A very small part of this portion comes from the hands of arsonists, people with a psychological disorder that causes them attraction to fire and its effects.

Another modest part, comes from revenge in disputes between landowners, but the greater part corresponds to practices such as the regeneration of pastures or the burning of stubble, the opening of areas to favor hunting or to scare off wolves and other threats. These practices are especially rooted in the Spanish northwest, but they also occur throughout the peninsula and the world in general.

The controlled use of fire is, a priori, beneficial to help various plant species to germinate or develop natural features, such as oak cork. This use, however, is no longer beneficial because it is either abused or used in a way that would work in a climate like that of the early twentieth century, but not in a climate like today’s, which is more unstable.

Fires are one of the many factors that enhance the greenhouse effect and, in turn, are enhanced by it, creating a vicious cycle that can worsen if left unchecked. But it should also be noted that there are other reasons, some of them more decisive, for causing fires. These reasons are particularly pronounced in the Iberian northwest, making it the peninsular area with the highest risk for sixth-generation fires.