Guejito Fire Essay
2007 San Diego Fire Season: The Witch Creek and Guejito Fires The Witch Creek Fire (WCF) took place in San Diego County on October 21st 2007 ("Witch Creek Investigation Report"). The exact location of the fire within the county was the witch creek area, just east of the Southern California town of Ramona ("Witch Creek Investigation Report"). This fire was believed to have been started around noon of that day ("Witch Creek Investigation Report"). The Guejito fire was discovered near Guejito bridge in the NW corner of Rancho Bernardo on Oct. 22nd, at around 1pm (Kochanski et al, 2009). A witness to the fires noted that the Guejito burned the North-East portion of his land and a couple of hours later the WCF advanced from the South-East and destroyed the rest of his property (Kochanski et al, 2009). The Witch and Guejito fires quickly merged, burning 80,000 ha, destroying 1141 homes and causing two fatalities (Mitchell, 2013). The combined fire ranks as the fifth largest and third most destructive in California’s recorded history (Mitchell, 2013).
In the case of the WCF, it was determined that the cause of ignition was electrical line arcing. The Guejito fire started half a day later than the WCF and was ignited by energized power lines that came into contact …show more content…
with lashing wire. (Maranghides et al, 2009) When the two conductors clashed they emitted plasma or molten/flaming droplets (Mitchell, 2013) that ignited adjacent vegetation. Powerline arcing accounts for roughly 1% of all wildfire ignition but, under extreme weather conditions, can become an important source (Mitchell, 2013). One of the main reasons the fires become so large and devastating was due to the timing of ignition (Mitchell, 2013). Both fires took place in late autumn at the point when vegetation is at its driest and most vulnerable (Maranghides et al, 2009). Strong winds were directly responsible for arcing said powerlines and also worked to spread the fire rapidly (Mitchell, 2013). Wind Powered
The Santa Ana winds peak in midwinter (Cao et al, 2016) but fuel the most destructive events which take place in the fall months, (Conard et al, 1998) before winter rains persist (Cao and Fovell). During this time the vegetation is particularly dry and, fire danger increases due to the combinatory effect of strong winds and low humidity (Cao et al, 2016). Large fires in the area are usually associated with these high winds (Conard et al, 1998). Wind may play an important role in the spread of fire but, there are other factors that determine spread within the chaparral and other vegetation type that are not well understood (Conard et al, 1998).
Kochanski et al. obtained weather data collected from the University of Utah which revealed that on the day of both fires respective ignitions, the relative humidity was severely altered by shifts in wind speed (Maranghides et al, 2009). (Above: Image depicting Santa Ana winds from High pressure cell of the Great Basin; source: islandnet.com)
At a weather station 10 km due east of the site of the WCF, relative humidity measured at 30-40% before shifting winds lowered it to 16% just prior to the ignition; less than 20 minutes before ignition, 38km/h wind speeds and gusts up to 69km/h were recorded (Maranghides et al, 2009). Similarly, at a weather station 2km south west of the Guejito fire origin, data showed that the relative humidity of the area dropped from 100% to 15% and that wind speeds increased from 11km/h to 36km/h. (Maranghides et al, 2009). In Southern California the terrain is rugged and variable; this variability generates wind disturbances (Keeley et al, 2001) characterized as being relatively intense and are referred to as “Downslope windstorms” (Cao et al, 2016). These gusts of downslope wind can exceed 100 km/h in some areas and aid in fires ability to spread rapidly throughout the region (Cao et al, 2016). Winds exceeding 45 km/h are up to eight times more likely to drive fire beyond ability to be suppressed (Mitchell, 2013). The gusts are so intense that they commonly topple trees and power lines (Cao et al, 2016), the latter of which has been identified as the root cause of both the Witch Creek and Guejito fires. Typically downslope windstorms require sufficiently large mountain barriers which create corridors that channel wind, increasing its velocity (Cao et al, 2016). The smaller, less prominent, mountain elevations of San Diego can generate comparable flow rates to this gale phenomenon (Cao et al, 2016).
Biologic Impacts
The vegetation found within the perimeter of the WCF was variable in composition and density; CALFIRE reported 13 different fuel types ("Witch Creek Investigation Report"). The Highland Valley, location of the WCF, is mostly barren with brush comprising the western portion and agricultural lands on the eastern (Maranghides et al, 2009). A mount adjacent to the Highland Valley with a community called “The Trails” on it, which was affected by the fire, is surrounded by stands of Hardwood and long-pole pine (P. contortus) to both the North and West (Maranghides et al, 2009). The eastern side of the mount is mostly brush with intermittent patches of grass (Maranghides et al, 2009).
(Above: Vegetation impact map for both WCF and Guejito fires; Red and yellow area represent Coastal sage and chaparral communities; source: San Diego State University)
Coastal sage scrub and chaparral that occurred on sloped upland areas within the perimeter of the Witch and Guejito fires were hit hardest (“Witch Creek Biological Impacts”). Chaparral is the dominant vegetation type on low to middle elevations found throughout the southwest and consists of evergreen shrub species belonging to multiple genera (Conard et al, 1998). Both the chaparral and coastal sage species are fire adapted but, there is concern that an increase in fire frequency may alter the vegetation composition from shrub-land habitat to one dominated by non-native grasses (“Witch Creek Biological Impacts”). Bird species such as the California Gnatcatcher rely on sage scrub for habitat, and when the scrub is greatly reduced by fire their populations decline (“Witch Creek Biological Impacts”). A shift away from the upland scrub community to grassland may cause a localized extinction of the gnatcatcher and other bird species.
Prickly pear (Opuntia littoralis) and Coastal cholla (O. prolifera) communities within perimeter of the fires were severely impacted (“Witch Creek Biological Impacts”). Prickly pear and cholla are less well adapted to fire than chaparral, and thus need ample time in between events to recover (“Witch Creek Biological Impacts”). Species such as the Cactus wren require cactus to be at least a meter tall to be considered suitable habitat (“Witch Creek Biological Impacts”). With an increased fire frequency there is not enough time for the cactuses to regenerate (“Witch Creek Biological Impacts”) and this may push those species reliant upon them out of the region.
Grassland species usually recover well post-fire (“Witch Creek Biological Impacts”). However, in the processes of building fire breaks and in post-fire remediation of the burned areas, bulldozers were utilized (“Witch Creek Biological Impacts”). There is concern that the bulldozers disturbed the soil enough that invasive grasses could potentially colonize these sites (“Witch Creek Biological Impacts”) and outcompete native species. Select vernal pool habitat within cities of Ramona, Rancho Guejito and Santa Fe Valley were affected by the WCF (“Witch Creek Biological Impacts”). Vernal pools result when water collects in depressions that have impermeable layers beneath them, restricting infiltration ("California's Vernal Pools."). The ephemeral pools are ecologically important because they harbor a diverse array of native flora and faunal communities ("California's Vernal Pools.").
Fire regime: Past and Present
Southern California’s fire regime history is characterized by many small fires with the occasional large landscape-altering shrub-land crown fire (Keeley et al, 2001). The largest of these fires account for over 90% of the area burned within the chaparral ecosystem (Strauss et al., 1989). Chaparral has an intermediate fire-return interval (Conard et al, 1998). Historically, the stand-replacing fires occurred every 20 to 40 years (Keeley et al, 2001). These larger fires are resultant of weather generated by Foehn-type Santa Ana winds (Keeley et al, 2001). The winds are capable of driving fire through any age-class of fuel (Keeley et al, 2001) even the relatively nonflammable mature stands (Conard et al, 1998). Fire intensity and severity depend upon such factors as these Santa Ana derived wind as well as adequate precipitation, fuel type and topography and so have always been considered variable (Keeley et al, 2001).
In the pre-suppression era, fires within the chaparral were always stand-replacing but burned irregularly; potentially creeping upon the surface or raging among the crown (Keeley et al, 2001). The main difference between the historical regime and our contemporary one is the rate of human caused ignition and thus shorter return intervals. As Keeley et al. (2001) has mentioned in a bevy of literature, simply put, humans have a profound effect upon fire frequency and can greatly alter burning patterns. The human influence is most prominent in the wildland-urban interface between chaparral and coastal epicenters (Keeley et al, 2001). This influence wains in the hard to reach high-elevation inland areas (Keeley et al, 2001). Changes in climate are suspected to have influenced the fire-return interval as well (Keeley et al, 2001) so the blame does not rest squarely upon the shoulders of humanity.
Prior to the high rate of human induced ignitions of contemporary times, lightning was the primary ignition source of chaparral fire (Conard et al, 1998). Human ignitions in the fall have likely come to replace lightning ignited fire as the primary driver of the large-scale events that take place when conditions are optimum (Conard et al, 1998). These lightning ignited fires of the past, although infrequent in the coastal regions, would burn for months at a time (Keeley et al, 2001). Even over this span the fires burned a modest amount of land (Keeley et al, 2001). They would either be extinguished by rain or natural barriers (Keeley et al, 2001). Some remnants of the fire would “hold-over” in canyons, tree stumps etc. until the Santa Ana’s picked up in late autumn (Conard et al, 1998) ; the winds would use this source to fuel massive scale fires that could burn up to 30,000 ha in a single day, sometimes for multiple days on end (Keeley et al, 2001).
Conclusion
Massive scale fires driven by autumnal foehn winds are a natural function of the southern California fire regime.
The heterogeneous topography of the region, working in unison with inland high and coastal low pressure cells, generate winds that can measure up to 100 km/h. Winds of this speed alter humidity in a way that increases susceptibility of vegetation to fire ignition. Furthermore, the winds are strong enough to cause power lines to arc, ejecting molten material that easily ignite dry plant fuels. Thus, the source of ignition and the increased amount of ignition events, both directly and indirectly caused by humans, are a significant change to the historic regime aside from a gradually warming
climate.
Fire intensity and severity in the region have always been variable and are dependent on a multitude of factors including weather, topography, precipitation, and fuel type. Management, specifically suppression, reduced average fire size in the latter part of the 20th century but, has done little else to impact the historic fire regime. In fact, human induced ignition is so persistent that without suppression, chaparral ecosystems would likely convert to non-native grassland given the opportunity. Many endemic species require chaparral as their primary habitat and the loss of this habitat could cause local extinctions without human interjection.
In the case of the WCF, it was determined that the cause of ignition was electrical line arcing. The Guejito fire started half a day later than the WCF and was ignited by energized power lines that came into contact …show more content…
with lashing wire. (Maranghides et al, 2009) When the two conductors clashed they emitted plasma or molten/flaming droplets (Mitchell, 2013) that ignited adjacent vegetation. Powerline arcing accounts for roughly 1% of all wildfire ignition but, under extreme weather conditions, can become an important source (Mitchell, 2013). One of the main reasons the fires become so large and devastating was due to the timing of ignition (Mitchell, 2013). Both fires took place in late autumn at the point when vegetation is at its driest and most vulnerable (Maranghides et al, 2009). Strong winds were directly responsible for arcing said powerlines and also worked to spread the fire rapidly (Mitchell, 2013). Wind Powered
The Santa Ana winds peak in midwinter (Cao et al, 2016) but fuel the most destructive events which take place in the fall months, (Conard et al, 1998) before winter rains persist (Cao and Fovell). During this time the vegetation is particularly dry and, fire danger increases due to the combinatory effect of strong winds and low humidity (Cao et al, 2016). Large fires in the area are usually associated with these high winds (Conard et al, 1998). Wind may play an important role in the spread of fire but, there are other factors that determine spread within the chaparral and other vegetation type that are not well understood (Conard et al, 1998).
Kochanski et al. obtained weather data collected from the University of Utah which revealed that on the day of both fires respective ignitions, the relative humidity was severely altered by shifts in wind speed (Maranghides et al, 2009). (Above: Image depicting Santa Ana winds from High pressure cell of the Great Basin; source: islandnet.com)
At a weather station 10 km due east of the site of the WCF, relative humidity measured at 30-40% before shifting winds lowered it to 16% just prior to the ignition; less than 20 minutes before ignition, 38km/h wind speeds and gusts up to 69km/h were recorded (Maranghides et al, 2009). Similarly, at a weather station 2km south west of the Guejito fire origin, data showed that the relative humidity of the area dropped from 100% to 15% and that wind speeds increased from 11km/h to 36km/h. (Maranghides et al, 2009). In Southern California the terrain is rugged and variable; this variability generates wind disturbances (Keeley et al, 2001) characterized as being relatively intense and are referred to as “Downslope windstorms” (Cao et al, 2016). These gusts of downslope wind can exceed 100 km/h in some areas and aid in fires ability to spread rapidly throughout the region (Cao et al, 2016). Winds exceeding 45 km/h are up to eight times more likely to drive fire beyond ability to be suppressed (Mitchell, 2013). The gusts are so intense that they commonly topple trees and power lines (Cao et al, 2016), the latter of which has been identified as the root cause of both the Witch Creek and Guejito fires. Typically downslope windstorms require sufficiently large mountain barriers which create corridors that channel wind, increasing its velocity (Cao et al, 2016). The smaller, less prominent, mountain elevations of San Diego can generate comparable flow rates to this gale phenomenon (Cao et al, 2016).
Biologic Impacts
The vegetation found within the perimeter of the WCF was variable in composition and density; CALFIRE reported 13 different fuel types ("Witch Creek Investigation Report"). The Highland Valley, location of the WCF, is mostly barren with brush comprising the western portion and agricultural lands on the eastern (Maranghides et al, 2009). A mount adjacent to the Highland Valley with a community called “The Trails” on it, which was affected by the fire, is surrounded by stands of Hardwood and long-pole pine (P. contortus) to both the North and West (Maranghides et al, 2009). The eastern side of the mount is mostly brush with intermittent patches of grass (Maranghides et al, 2009).
(Above: Vegetation impact map for both WCF and Guejito fires; Red and yellow area represent Coastal sage and chaparral communities; source: San Diego State University)
Coastal sage scrub and chaparral that occurred on sloped upland areas within the perimeter of the Witch and Guejito fires were hit hardest (“Witch Creek Biological Impacts”). Chaparral is the dominant vegetation type on low to middle elevations found throughout the southwest and consists of evergreen shrub species belonging to multiple genera (Conard et al, 1998). Both the chaparral and coastal sage species are fire adapted but, there is concern that an increase in fire frequency may alter the vegetation composition from shrub-land habitat to one dominated by non-native grasses (“Witch Creek Biological Impacts”). Bird species such as the California Gnatcatcher rely on sage scrub for habitat, and when the scrub is greatly reduced by fire their populations decline (“Witch Creek Biological Impacts”). A shift away from the upland scrub community to grassland may cause a localized extinction of the gnatcatcher and other bird species.
Prickly pear (Opuntia littoralis) and Coastal cholla (O. prolifera) communities within perimeter of the fires were severely impacted (“Witch Creek Biological Impacts”). Prickly pear and cholla are less well adapted to fire than chaparral, and thus need ample time in between events to recover (“Witch Creek Biological Impacts”). Species such as the Cactus wren require cactus to be at least a meter tall to be considered suitable habitat (“Witch Creek Biological Impacts”). With an increased fire frequency there is not enough time for the cactuses to regenerate (“Witch Creek Biological Impacts”) and this may push those species reliant upon them out of the region.
Grassland species usually recover well post-fire (“Witch Creek Biological Impacts”). However, in the processes of building fire breaks and in post-fire remediation of the burned areas, bulldozers were utilized (“Witch Creek Biological Impacts”). There is concern that the bulldozers disturbed the soil enough that invasive grasses could potentially colonize these sites (“Witch Creek Biological Impacts”) and outcompete native species. Select vernal pool habitat within cities of Ramona, Rancho Guejito and Santa Fe Valley were affected by the WCF (“Witch Creek Biological Impacts”). Vernal pools result when water collects in depressions that have impermeable layers beneath them, restricting infiltration ("California's Vernal Pools."). The ephemeral pools are ecologically important because they harbor a diverse array of native flora and faunal communities ("California's Vernal Pools.").
Fire regime: Past and Present
Southern California’s fire regime history is characterized by many small fires with the occasional large landscape-altering shrub-land crown fire (Keeley et al, 2001). The largest of these fires account for over 90% of the area burned within the chaparral ecosystem (Strauss et al., 1989). Chaparral has an intermediate fire-return interval (Conard et al, 1998). Historically, the stand-replacing fires occurred every 20 to 40 years (Keeley et al, 2001). These larger fires are resultant of weather generated by Foehn-type Santa Ana winds (Keeley et al, 2001). The winds are capable of driving fire through any age-class of fuel (Keeley et al, 2001) even the relatively nonflammable mature stands (Conard et al, 1998). Fire intensity and severity depend upon such factors as these Santa Ana derived wind as well as adequate precipitation, fuel type and topography and so have always been considered variable (Keeley et al, 2001).
In the pre-suppression era, fires within the chaparral were always stand-replacing but burned irregularly; potentially creeping upon the surface or raging among the crown (Keeley et al, 2001). The main difference between the historical regime and our contemporary one is the rate of human caused ignition and thus shorter return intervals. As Keeley et al. (2001) has mentioned in a bevy of literature, simply put, humans have a profound effect upon fire frequency and can greatly alter burning patterns. The human influence is most prominent in the wildland-urban interface between chaparral and coastal epicenters (Keeley et al, 2001). This influence wains in the hard to reach high-elevation inland areas (Keeley et al, 2001). Changes in climate are suspected to have influenced the fire-return interval as well (Keeley et al, 2001) so the blame does not rest squarely upon the shoulders of humanity.
Prior to the high rate of human induced ignitions of contemporary times, lightning was the primary ignition source of chaparral fire (Conard et al, 1998). Human ignitions in the fall have likely come to replace lightning ignited fire as the primary driver of the large-scale events that take place when conditions are optimum (Conard et al, 1998). These lightning ignited fires of the past, although infrequent in the coastal regions, would burn for months at a time (Keeley et al, 2001). Even over this span the fires burned a modest amount of land (Keeley et al, 2001). They would either be extinguished by rain or natural barriers (Keeley et al, 2001). Some remnants of the fire would “hold-over” in canyons, tree stumps etc. until the Santa Ana’s picked up in late autumn (Conard et al, 1998) ; the winds would use this source to fuel massive scale fires that could burn up to 30,000 ha in a single day, sometimes for multiple days on end (Keeley et al, 2001).
Conclusion
Massive scale fires driven by autumnal foehn winds are a natural function of the southern California fire regime.
The heterogeneous topography of the region, working in unison with inland high and coastal low pressure cells, generate winds that can measure up to 100 km/h. Winds of this speed alter humidity in a way that increases susceptibility of vegetation to fire ignition. Furthermore, the winds are strong enough to cause power lines to arc, ejecting molten material that easily ignite dry plant fuels. Thus, the source of ignition and the increased amount of ignition events, both directly and indirectly caused by humans, are a significant change to the historic regime aside from a gradually warming
climate.
Fire intensity and severity in the region have always been variable and are dependent on a multitude of factors including weather, topography, precipitation, and fuel type. Management, specifically suppression, reduced average fire size in the latter part of the 20th century but, has done little else to impact the historic fire regime. In fact, human induced ignition is so persistent that without suppression, chaparral ecosystems would likely convert to non-native grassland given the opportunity. Many endemic species require chaparral as their primary habitat and the loss of this habitat could cause local extinctions without human interjection.