Results
There is an accumulation of unhealthy to moderately healthy vegetation in and around Topanga Canyon, which is likely because the area has had no recent historic fires. Dry and stressed vegetation is more likely to burn. Topanga Canyon has factors in addition to this that place it at risk of a major fire in the near future. These factors are the single evacuation route, the canyon topography, and the Santa Ana winds.
Historic Fire Map
We first analyzed wildfires in the Santa Monica Mountains since 1992 using historic fire data from the LA County Fire Department. The map shows that there have been many fires in the west and central portion of the Santa Monica Mountains. However, there have been none in the most eastern portion of the mountains and none in Topanga Canyon itself since 1993.
Topanga Canyon Vegetation
Landsat 8 - Bands 6,5,4
This band combination is useful for vegetation studies. Vegetation is visualized as green and soils as brown. The image shows that the Topanga Canyon area is relatively green compared to the rest of the Santa Monica Mountains. This is likely because Topanga Canyon is the only area left in the mountains that has not recently burned. As a consequence of no recent historic fires, vegetation has been able to accumulate.
Santa Monica Mountains NDVI
The results of the NDVI analysis of the entire Santa Monica Mountains show that the NDVI value is much lower in the east, in the Topanga area but even more so in the area to the right of that. This is important because although Topanga may be more densely vegetated than the rest of the mountains, this vegetation may not be entirely healthy. Lower positive NDVI values are an indicator of unhealthy and dry vegetation.
Topanga Canyon NDVI
The mean NDVI value for the Topanga Canyon area specifically is approximately 0.37. Within the -1 to 1 range of NDVI values, -1 to 0 is classified as dead plants or inanimate objects, 0 to 0.33 is classified as unhealthy plants, 0.33 to 0.66 is classified as moderately healthy plants, and 0.66 to 1 is classified as healthy plants. Topanga Canyon's value of 0.37 would place its vegetation classification in the moderately healthy class. However, it is very close to falling within the unhealthy plant classification. This thus demonstrates fire risk in the area because drier and more stressed vegetation is more likely to burn. Therefore, if Topanga is densely vegetated with relatively unhealthy vegetation, it faces increased risk of burning.
3D Visualization of Topanga Canyon
This 3D visualization simulates the actual topography of Topanga Canyon. In red is Topanga's single evacuation route. The green arrows indicate the direction of the Santa Ana winds in relation to Topanga Canyon. The Santa Ana winds are high-speed and dangerous northeasterly winds that periodically blow from the coast mountain ranges to the beach. These winds typically peak in October, which also falls within the California Fire Season. This means that if a fire were to occur in this area at the same time as strong, dry winds such as the Santa Anas, it would blow down into the canyon and quickly sweep through and devastate the entire area. This would all likely happen before the residents have finished evacuation.
