one 2022





Firefighters tackle an underground fire in Cuesta del Ternero – El Boquete complex on April 4, 2021. PHOTO BY PABLO ALCORTA BRIGANTI.


The Andean Patagonian Region mountains experienced some of the most devastating wildfires in Argentina’s recent history during the summer of 2021. Extreme fires, although not new for the region (Chile 2017, Argentina 2018, Bolivia 2019), are clear indicators of change for the worse. Until now, fires were on the dry pampa or hilly forested areas, not in the alpine ecosystems of the Andes. Climate trends and these fires point to a near future with bigger fire storms. This extreme is also confirmed by recent events in the Chilean region. An analysis of the incidents and lessons learned show the wildland urban interface putting increasing pressure on the area, and therefore stress for responders. Attention must be paid to the metres-deep organic soil layer, which is becoming a clear driver of long-lasting fires. A PyroCb event, which was unexpected due to strong wind and highly stable atmosphere over the area, is also matter of concern.



In less than two months in the summer of 2021, the two largest wildfire complexes in Argentina in recent years occurred in the 42nd Parallel Andean Region, a micro-region in Northwest Argentina that includes six main towns and their rural areas. 

One of these fires turned out to be a wildland urban interface (WUI) fire, with hundreds of homes destroyed, and fatalities, giving it the dubious distinction of being among such tragic fires as Santa Rosa (U.S., 2017), Kineta (Greece, 2018) and Pedrógão Grande (Portugal, 2017). 

The events of 2021 can be classified as sixth-generation fires, with characteristics similar to Las Máquinas and Agua Fría (Chile, 2017 and 2020), El Tajamar (Argentina 2018), Roboré and Otuquis National Park (Bolivia 2019 and 2020). Sixth-generation fires are said to be a consequence of the interaction of climactic and atmospheric conditions; rather than depending on external factors, such as wind, to spread, these fires find their own paths and are unpredictable. Another definition of a sixth-generation fire is an area of more than 5,000 hectares burned, along with aggressiveness, in conjunction with bad weather.

The 42nd Parallel Andean Region is characterized by its glacial valleys surrounded by high peaks, permanent snow, and lakes. The climate is temperate, although on warmer days the temperature can rise to 30 C (86 F). Winds are predominantly from the west-northwest. Summer is dry, and the most contrasting climatic variation in this area is rainfall, which decreases dramatically from west to east, due to the mountains that function as natural barriers to the humid winds from the Pacific. This directly influences the geographic distribution of different types of vegetation, and it is translated into the existence of diverse environments just a few kilometers apart: the Andean Patagonian Forest followed by a transition area, the “ecotone,” and finally, further east, the steppe, a large area of flat grassland. Although native species predominate (most of the area is covered by mixed forests dominated by Chilean cedar-Southern Beech (Austrocedrus–Nothofagu), in some spots, there are exotic species such as ponderosa pine, Rocky Mountain lodgepole pine, and Douglas fir).

In this region, the primary employer is government administration, followed by tourism and leisure activities. The region boasts intensive agriculture, with the production of berries and hops. Since the 1990s, timber and extensive livestock production have declined. 

Due to the beauty of the landscape, the region has experienced land subdivision; property is valued more as a real-estate resource than a productive one. Wealthy families from the main cities in Argentina have moved in, with the vision of living in a place that is presumably safer and allows them to be in contact with nature, but they do not take up the traditional uses of the rural land. Therefore, expansion of the city has accelerated, incorporating new social patterns, and configuring new wildland urban interface areas of increasing complexity.

Layer’s source: Godoy, M.M.; Martinuzzi, S; Kramer, H.A.; Defossé, G.E.; Argañaraz, J. & Radeloff, V.C.; (2019), Rapid WUI growth in a natural amenity-rich region in central-western Patagonia, Argentina; International Journal of Wildland Fire, n28, 473-484.


The pressure of a greater population over the landscape results in more roads, most of them narrow and winding, and sometimes with steep slopes; the houses are mainly made of wood, and are built in the forest without respect for the risks of fires; new overhead power lines end up being in contact with the tree branches, frequently causing fires, especially on windy days; and given the increase in wildfire ignitions , there is an insufficient water supply.

In addition, people are vulnerable because they come from cities and have never experienced a wildfire; thus, their perception of the risk of living in the WUI is skewed by their deeper interest of being part of the idyllic landscape, surrounded by greenery and wildlife. 



Of course, there were wildfires before; in some cases, fires affected almost as much area as was burned by each of the 2021 events. But during the 2021 fire season, two characteristics were different from previous events: groundfire persistence (Cuesta del Ternero – El Boquete complex)); and the elevated rate of spread (Las Golondrinas – Radal complex).


Top: plot with both fires behavior comparison (in terms of affected areas, rates of spread and time being active). Botton: 2021 fires isochrones and closest historic fires perimeters (1980-2020) map.



On Jan. 24, the Cuesta del Ternero fire was human caused, and within 24 hours, the fire perimeter had burned beyond the limit of Río Negro province. Because the wildfire had spread such a long distance another jurisdiction became involved in the fire suppression effort. The development of a PyroCu (pyrocumulous cloud caused by a wildfire) was observed that evening, after which the fire made its big run. During the next couple of days, there was minimal fire growth, but it was a dangerous situation for firefighters working in deep ravines on steep zones with complex topography. 

On Feb. 6 and 7, part of the fire, near the tail, was reactivated due to the strong winds from the east-northeast. Homes in an Indigenous community were at risk from the fire, and if the appropriate maneuvers had not been carried out, the western slope of the Piltriquitron mountain and various surrounding neighborhoods could have been strongly affected. 

On Feb. 23, the fire was deemed controlled and soon after, extinguished. However, on March 7, a new wildfire ignited (El Boquete) and it was presumed that it may have been a reactivation of the Cuesta del Ternero fire, because of the strong winds that day (more than 90 km/h). On March 9, the Cuesta del Ternero fire demonstrated a remarkably high rate of spread, and the wildfire again crossed Río Negro province limits, towards the jurisdiction of Chubut, threatening the town of El Maitén. This fire was extinguished May 28, affecting a total area of 15,710 ha (38,820 acres).


March 9th, 10 am. Extreme fire behavior. Views of the flame characteristics. Intensity values are estimated to be around 60,000 kw/m. Ph: Ariel Amthauer



On March 9 at 1600 hours, the Las Golondrinas fire started. One hour later, the El Radal Fire began just four kilometers away. At 1800 hours, this new fire was absorbed by the first one, causing extreme fire behaviour. During the next five hours, this complex fire did its biggest run – 23 kilometers – and after that, without growing noticeably, kept burning very slowly. Las Golondrinas – El Radal was deemed controlled on April 4, with a total affected area of 12,580 ha (31085 acres).



1. Weather conditions and fire environment

The risk caused by pre-fire conditions in the areas of the two 2021 fires significantly contrasted with the fire weather index. The availability of fine fuels that burn easily (Fine Fuel Moisture Code values exceeding 90, which are associated with ease of ignition), the significant participation of coarse fuels in the combustion process (Buildup Index and Drought Code values), and drought conditions in the region indicated evidence of continuing fire in deep soil layers. 

These characteristics allow us to understand how, in a closed and unmanaged forest with high fuel load and continuity, and where the depth of the mulch was close to one meter, the fire remained dormant for three weeks, penetrating the dry organic layer and being reactivated when the meteorological conditions allowed it – mainly high temperatures and drought conditions, but with the addition of strong winds with gusts of 90 km/h.

On the other hand, the high availability of the fine fuel explains the quick rate of spread and the generation of multiple hotspots. Similar to the El Tajamar fire (La Pampa, Argentina) in 2028, Las Golondrinas fire developed a PyroCb (pyrocumulonimbus) at night, associated with the arrival of humidity from the west, facilitating the buoyancy of the column that, until then, was flattened by the wind, and from that point, reached the moment of maximum pyroconvectivity and extreme behavior.


2. Weeks versus hours

An interesting comparison is that although the surfaces affected were relatively similar, the duration of these fires was completely different. In that sense, while Cuesta del Ternero remained active for a month and a half, Las Golondrinas – El Radal, characterized as a firestorm due to its speed and intensity (greater than 60.000 kw/m), advanced in a few hours from its beginning, 33 kilometers (at a rate of spread of 6 km/h and with averages of 10 km/h, at the critical moment), and in that short period of time, developed a PyroCu that transitioned to PyroCb.

The occurrence of these fires, along with those in Australia (2020) or California (2021), shows us the diversity of environments where these fires can be expected. Until now, these fires were associated with plains areas of grasslands and open vegetation, such as La Pampa or the Chiquitano chaco, but dense forests and steeper slopes came also into play. Additionally, the high spread rate of these wildfires implies increased risks for everybody, not only the firefighters working on the fields under possible entrapments, but also the population that is aligned with the direction of spread of the fire. In both cases, it’s key to be aware of the situation and know the escape routes.  


Classification of each fire isochrone, based on the extreme wildfire events classification proposed by Alexander & Lanoville. Predicting Fire Behavior in the Black Spruce-Lichen Woodland Fuel Type of Western and Northern Canada. Forestry Canada.


3.Wildfire impacts: rural areas and WUI

As mentioned, the region has experienced a significant increase in its population in recent years, not concentrated in main urban or suburban housing developments, but scattered throughout the entire territory. This sprawl makes a large portion of residents highly vulnerable to wildfires.

The two fires also presented their differences. Cuesta del Ternero – El Boquete complex affected forest masses and rural areas, with the consequent loss of forest plantations, land suitable for grazing, cattle, sheds, and two houses. In contrast, Las Golondrinas-Radal complex fire generated an extreme impact on the wildland urban interface areas of Las Golondrinas, Cerro Radal and El Hoyo neighborhoods, destroying the existing infrastructure while the fire was spreading across the terrain – fences, powerlines, sheds, and 511 houses, in addition to dozens of injuries and three civilian fatalities (one of them trapped by the fire). 



Society is facing, on a global scale, fires that are far more intense than people or firefighters are used to. Remarkably high rates of spread, the development of convective columns that result in a PyroCu and sometimes a PyroCb, and the massive destruction of the environment are all indicative of sixth-generation category fires. 

As had been witnessed in California (2020), Bolivia (2019), Chile (2017) and in 2021 in Europe (Greece, Italy, France, Belgium, Spain), climate change has played a main role in creating the perfect conditions for these big fires to occur. In the Cuesta del Ternero – El Boquete complex fire, the long dry period, the high temperatures, and the strong winds influenced not only the availability of fuels above the ground but also the deeper organic layer, helping the development of ground fires and explaining why the fire remained latent for more than three weeks, and the subsequent reactivation and spread over 8,000 hetares.

These sixth-generation fires are capable of surpassing the attack speed and operational capacity of traditional fire suppression organizations and practices; they require many resources over long durations and demonstrate higher rates of spread and unpredictable fire behavior, resulting in greater risk for the people working on the field, potential fatalities due to lack of situational awareness, and therefore, entrapments.

This important change in the environmental conditions and consequently, fire behavior, exposes the need to change the way people relate to the environment, the way fire management agencies try to accomplish their missions, and the way we forecast dangerous fire behaviors and conditions for the people fighting fire in the field, and the society in general. 

The poor perception of risk by a significant portion of the population living in WUI areas and consequently, the existence of extremely high-risk zones, is why it is key for wildfire management agencies to make residents aware of the dangers and risks. This can be done through ongoing environmental education programs and awareness campaigns but must be accompanied by the participation of different social actors and all levels of government, which must implement consistent local policies, legislate and enforce those policies, and pursue the development of a resilient landscape, economy, and society.



Mercedes Bachfischer is a wildfire data analyst at The Emergency Program (TEP), Spain.

Marc Castellnou is fire analyst chief at Catalan Fire and Rescue Service, Spain.

Nicolás de Agostini is deputy chief at Wildfires Fight and Prevention Service, Río Negro, Argentina.