**Abstract**

One of the causes of a forest fire is a combination of environmental variables such as temperature and relative humidity, as well as wind speed. When environmental conditions are favorable, chemical reactions occur at the forest mass level, resulting in pre-ignition. A big-data analysis of three spontaneous forest fires that occurred in Spain between 2015 and 2019 was performed to determine the chemical compound from which the forest fire starts. After analyzing satellite data, it was discovered that the critical temperature at which a fire starts spontaneously is 51.27°C, a value that coincides with the maximum limit of decrease in environmental sulfur dioxide concentration ([SO2]), presumably due to sulfur capture by part of the wood, an element that is released into the environment after the fire occurs. The Spontaneous Forest Fire Process (SFFP) and fAPAR have a close relationship because pre-ignition occurs when the critical temperature determined by environmental conditions is reached.

**Keywords:** sulfur dioxide, thermal plugging, Broglie Law, Iberian Peninsula, remote sensing technologies

### **1. Introduction**

Hitherto, when a forest fire occurs, the habitat is destroyed, without it being possible to avoid the devastation of the environment when the fire is due to natural causes.

According to Government of Spain [1], Spanish forest ecosystems occupy just over 26 million hectares (26,280.281 ha), of which almost 15 million (14,717.898 ha) are wooded and some 12 (11,562.382 ha) treeless, which respectively represent 29 and 23% of the national territory. The coniferous forests have a similar extension than the hardwood ones (5.7 and 5.2 million hectares, respectively) while the mixed ones have a somewhat smaller population (3.9 million hectares).

In another vein, and based on the latest study published by [2], it is of great interest to take into account the deforestation linked to international trade, especially since Spain causes the deforestation of 32,900 hectares of forest each year (the production and consumption of soybeans, palm oil and beef are the main items that explain this situation). However, at the national level, a notable increase in the area of wooded mountains has been detected at the cost of a decrease in the cultivated area, as well as that corresponding to land without forest mass [1]. In general terms, the Government of Spain has action policies to control both deforestation and forest conversion to other uses through the sustainable use of its resources. In this regard, and although deforestation occurs as a result of the mutual interaction of various factors, the problem of a forest fire, as an independent variable, should not be ignored, since as consequence of the destruction of areas of both biological and ecological interest, it is difficult to adapt the damaged ecosystem to the situation prior to the fire.

In relation to the above, the trend that climate-change represents in the medium term is of enormous importance, since the increase in temperatures as well as the increase in the incidence of prolonged and intense drought periods will result in a decrease in relative humidity. in the atmosphere close to the forest mass, and therefore the appearance of suitable conditions for spontaneous forest fires to take place much more often than at present [3].

Likewise, it is important to take into account the relationship between the dynamics of the lower atmosphere and the movement of air resulting in large fires that favor the development of enormous plumes, generating a series of processes that give rise to a vertical transfer of matter and energy in turbulent movements and rapid [4]. On the other hand, it is interesting to know that, during a forest fire, high-risk situations are frequently generated when specific fire sources are created, associated or not, with sudden changes in direction or speed of the wind. It is evident that, when temperature, relative humidity and local wind speed take place together, the forest fire expansion danger increases, making extinction work difficult [5].

The importance of the type of fuel existing in the forest mass should not be forgotten. For this reason, it should be noted that in Spain the predominant hardwood species are *Quercus ilex*, followed by *Quercus pyrenaica, Quercus pubescens, Eucalyptus spp., Quercus suber, Fagus sylvatica, Quercus faginea, Quercus canariensis, Quercus robur, Quercus petraea and Castanea sativa*. Regarding conifers*, Pinus halepensis, Pinus pinaster, Pinus sylvestris, Pinus nigra* and *Pinus radiata* stand out. The great richness in scrub, bush and grass species existing in Spanish forests should not be forgotten, mainly due to the amount of dry matter that they can contribute to the fire.

According to [6], in this country, around 5% of fires are due to natural causes (adequate relationship between relative humidity and temperature, lightning, etc.), being the cause of the remaining 95% very varied, highlighting among them accidents or negligences, intentional fire and unknown reasons.

In another vein, and as a result of the technological advances that have occurred in recent decades, it is evident that remote sensing can be a tool of greater interest, than it is currently, in the evaluation and monitoring of forest fires. To date, satellite sensors collect data about the location of the fire, as well as those characteristics of the forest mass that may influence its duration and/or its extension [7]. As it is known, there are several satellites that inform us in almost real time of forest fires. One of the best known is NASA's MODIS (Moderate-Resolution Imaging Spectroradiometer), which is a scientific instrument on board both the Terra satellite and the Aqua satellite. Another of them is the VIIRS (Visible Infrared Imaging Radiometer Suite) also from NASA, a sensor on board of Suomi National Polar-orbiting (Suomi NPP) and NOAA-20, and which together with the MODIS provide data on forest fires within the NASA program, Fire Information for Resource Management System, dedicated exclusively to giving us timely and very precise information in near real time (NRT) of forest fires, within 3 hours after the passage of the satellite. The Sentinel satellites of the Copernicus program cannot be forgotten, a great help in this field of study carried out jointly by the European Space Agency (ESA) and by the European Union through *New Remote Sensing Technologies Applied to the Prediction of Spontaneous Forest Fires DOI: http://dx.doi.org/10.5772/intechopen.110501*

the European Environment Agency. ESA is currently developing seven missions, and has five underway, of which, each Sentinel mission is made up of two satellites to ensure total coverage in each mission.

As is well known, in many parts of the world most forest monitoring is still carried out using traditional methods, no existing information on the advantages of new and accurate remote sensing techniques. For this reason, it is very important to point out that there is currently no procedure, based on environmental information, capable of predicting those areas with a high probability of occurrence of a forest fire with time enough for the firefighting services can intervene before a major disaster occurs. Based on the comments, this study focuses on obtaining an algorithm, based on environmental information obtained through remote sensing, capable of predicting the moment in which the pre-ignition of a spontaneous forest fire occurs. The resulting algorithm can be useful for decision making, as well as preventing spontaneous forest fires.
