Research | Wildfire Risk at the Wildland Urban Interface

By: Francisca Yunis Richter

Published on June 15, 2023

In Chile, the areas where human populations and plant ecosystems coexist, are those with the highest risk of wildfires. These areas, called the urban-rural interface, comprise close to 5% of the national territory, but concentrate around 80% of the population and approximately 60% of the fires that occur in the country.

(González et al, 2020)

Source: Urban-rural interface zones in Chile are identified based on nationally defined thresholds and relative proportion of fires by region, inside and outside the proposed urban rural interface (González et al, 2020)
Source: National wildfire risk prediction map (Miranda et al, 2021)

The wildland urban interface is where human communities live with fire-prone vegetation cover. For example, a housing complex immediately adjacent to a forest plantation. Worldwide, it is in this space where wildfires cause the most significant number of deaths and losses of buildings and other infrastructure, so their identification and the evaluation of landscape management alternatives are of the utmost importance for territorial planning policies (Miranda et al, 2021).

Wildland urban interface interface zones have grown rapidly in recent decades, mainly due to urban expansion and population growth in rural areas. The growing threat of wildfires directly affects the residents of urban and peri-urban expansion areas of cities, where territorial planning becomes a fundamental axis to mitigate fire risks, as well as the adaptation of designs, locations, and characteristics of human settlements in the urban-rural interface (González-Mathiesen, March, Stanley, 2019).

The wildfire regime in Chile is characterized by intense fires during the months with higher temperatures and low rainfall, where the climate crisis increases drought and heat waves, increasing the frequency and intensity of fires. In the last decade, climate change has contributed to the ideal conditions for extreme and destructive wildfires, as well as the accumulation of fuel material, where dry vegetation increases in urban-rural interface areas, increasing the threat of wildfires ( CONAF, 2021). The probability of a fire occurring and its capacity to spread depend not only on the climate but also on the amount of fuel available, its flammability, and its distribution in the landscape. That is why changes in land use, by modifying the type and structure of the vegetation (the fuel), alter significantly the fire regime (González et al, 2020).

In Chile, wildfires are caused mainly by humans, either accidentally or by deliberate and intentional action. In fact, the occurrence of fires is closely related to the distance and location of urban centers and infrastructures such as roads, railways, and recreational sites, with urban-rural interface areas being especially relevant, since they increase the risk of fires (González et al., 2020). Although the climate crisis has increased the intensity and frequency of wildfires, at least 80% registered by the National Forestry Corporation (CONAF) are caused by humans.

Considering the potential increase in wildfires as a result of the climate crisis and land use changes, it is necessary to delimit the urban-rural interface areas in Chile and define those with a higher risk of wildfires in order to target policies of prevention, management, and combat, and mainly territorial planning, efficiently (Miranda et al, 2021).

Chile | Wildfire Season 2023

After the great wildfire in Viña del Mar at the end of 2022, the following months were devastating, where February began with fires that mainly affected the Ñuble, BioBío, and Araucanía regions, destroying more than 431,000 hectares, 3,218 homes, and 26 deceased. The registry of the National Forestry Corporation (CONAF), indicates that the hectares consumed during the 2022-2023 wildfire period have increased 7 times more, compared to the annual average of the seasons of the last 5 years (CONAF, 2023). The Biobío region was the most affected area, where the fire destroyed 1,773 homes, and the burned area exceeded 184,000 hectares, with 76% of the land being forestry plantations, 5% native forest, 10% bushes and 9% to agricultural crops and pastures. Within the most affected communes, Santa Juana has 42,858.97 damaged hectares, which is equivalent to 55.14% of its communal area. It is followed by Nacimiento, with 32,037.98 hectares, which is equal to 35 14% of the commune, and then Tomé, with 18,500.36 hectares, corresponding to 37.34% of its communal area. And if we add Mulchén, they represent 75% of all the fires that occurred in the Biobío Region (UdeC ,2023). According to the latest records published by CONAF, to date, 1.818 fires have been investigated nationwide, equivalent to 26% of all wildfires, according to the latest report from the Department of Prevention and Mitigation. In relation to the incidents investigated, 65 % (1.179) were classified as accidental or negligent, 33% (591) as intentional, and 2% (44) without a specific origin (CONAF, 2023).

Although the origin of the wildfires was due to human intervention, the weather was a fundamental factor for the fire behavior, which increased its intensity and frequency; According to the data obtained by the University of Chile, in the summer season, the highest temperatures in the country’s history were recorded, promoting the changing climate condition; recurring temperatures above 30ºC, increasing the frequency of heat waves, which created ideal weather conditions for wildfires, exacerbated by drought and high temperatures (Gallardo, 2023).

The frequency and intensity of rainfall, influenced by the climate crisis, are increasing droughts, therefore, the forests and low vegetation dry out, decreasing the percentage of moisture present in their composition, promoting the risk and vulnerability of human settlements related to wildfire events, especially in urban-rural interface areas (Fuentes, 2022). The abundant rains during 2022, showed levels above normal, compared to the last 5 years, which favored the growth of vegetation (mainly fine vegetation such as grasslands), which later dried up, during the months of higher temperatures, and became the main fuel for the ignition and expansion of wildfires (Fuentes, 2022).

The spatial distribution of wildfires is determined by the initial source of ignition and the direction and extension of the propagation. Both elements are conditioned, to a large extent, by the use of the land, which determines the amount and type of fuel that can be forests, forestry plantations, etc. It is important to consider that the origin of wildfires can occur outside the forest, such as on the edge of roads, rural properties, or even in urban areas adjacent to forestry territories (Garreaud, 2023). During the mega-fires of 2017, the records determined that close to 70% of the claims originated in areas with a high content of fine vegetation, which favored the spread of the fire, being comparable with the wildfires of 2023, which originated mainly in urban-rural interface areas close to forest plantations.

Currently, there are more than 40 areas vulnerable to the occurrence of wildfires in the south-central zone of the country, including 29 critical communes, a concept that is associated with urban-forest interface areas with a high incidence and probability of fire events. An important part of these higher-risk areas corresponds to rural areas close to populated centers where subdivisions have developed without much management of the territory. Some of the communes that concentrate the greatest number and density of wildfires are Valparaíso, Viña del Mar, Quilpué, Casablanca, El Quisco, El Tabo, San Antonio, Cartagena, Melipilla, Lota, Tomé, Coronel, Curanilahue, Penco, Lebu, Tirúa, Mulchén, Collipulli, Ercilla, Cabrero, Concepción, Cañete, Temuco, San Pedro de La Paz, Angol and Santa Juana, among others (Fuentes, 2022).

At the regional level, Biobío presents 116.145 burned hectares with plantations for industrial purposes, out of a total of 154.000. Regarding the native forest affected by the wildfires, the numbers are different since 7.934 hectares were burned (UdeC, 2023). Currently, the center-south of Chile has extensive areas of forestry plantations, which can form continuous units of 300.000 hectares, therefore, there is a latent risk for settlements near the urban-rural interface. Likewise, population growth and urban expansion towards these interface zones, mainly due to the construction of second homes, change in land use and scarcity of land in urban areas (CONAF, 2023), increases the risk of wildfires. , being mainly originated, either intentionally or accidentally, by humans.

Source: Wildfires investigated at the national level and the Biobío region (CONAF, 2023)
Source: Urban Resilience Plan in Rural Urban Interface (PRUIR) s.f
Source: Urban Resilience Plan in Rural Urban Interface (PRUIR) s.f
Source: Location of destroyed houses, Biobío Region. Report F2 Biobío Fires 2023

The “Santa Ana” wildfire in the Biobío region devastated more than 85.000 hectares, starting in the Nacimiento commune, and extending to Coronel and Santa Juana, which was the most affected area, concentrating the highest percentage of rural territory. “The commune of Santa Juana is located 48 kilometers from Concepción, and its surface area is 73.100 hectares, of which 1,49% belongs to the urban sector and the remaining 98,51% to the rural sector. According to the last census of 2017, 70% of its population lives in that small urban radius, and the remaining 30% lives in the broad rural sectors of the commune (Unda, 2023). According to the records of the Municipality of Santa Juana, the wildfires that occurred consumed more than 46.000 hectares, 59,7% of the total of the commune and 59,4% of the rural sector. The same registry of the Municipality, confirms that there were 13 deceased, 4.773 people affected, and 904 homes destroyed, although only 381 have been considered as “first home”. Likewise, almost half of those affected (2.042) belong to the 40% most vulnerable of the population (Unda, 2023).

Source: The flames consume a house during the early morning, near the city of Santa Juana (Chile) Photographer Pablo Hidalgo.


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