San Diego County, California: Effects of Wildfires Among Vegetation Kyle Garcia| krg2@txstate.edu*Department of Geography, Texas State University, San Marcos, TX

OVERVIEWThe two images that are being studied come from an image that is taken a year before the wildfire, and another image that’s taken a year after from the Landsat 5 sensor. These two images represent changes in vegetation as well as the burn severity for the county and are best expressed by the NBR algorithm as well as the NVDI algorithm. As far as calculating the change between these images for the vegetation, loss and regrowth, as well as just how intense the fires were in the year 2007. Models are programmed in Erdas Imagine to perform such tasks. Arcmap is used to create the thematic classifications for the burn severity and changes in NVDI.

Objectives• Show the counties burn severity index in a

thematic expression to better asses to what degree the fires impact on the landscape.

• Show the change in vegetation within the burn severity categories as well as the difference in vegetation growth between the year before the fires and after.

STUDY AREA

The study area takes place across the San Diego County (4,526 square miles across with a coordinate of 33.02°N 116.77°W.) The specific areas of interest are the locations that are associated damage and burn from the wildfires.

DATASETSLandsat 5 Imagery• LT50400372006267• LT50400372008017

San Diego County ShapefileCENSUS_TRACTS_2010

RESULTS1. Difference In Burn Ratio Classification 2.Difference Of NVDI In

Classes Of Burn Severity

Model To Subtract 2006 Image Burn Ratio with 2008 Image Burn Ratio

.

LegendBurn Severity IndexIndex

<-0.25

-0.25 to -0.1

-0.1 to 0.1

0.1 to 0.27

0.27 to 0.44

0.44 to 0.66

>0.66Ü 0 10 205 Miles

Coordinate System: NAD 1983 StatePlane California VI FIPS 0406 FeetProjection: Lambert Conformal Conic

Datum: North American 1983False Easting: 6,561,666.6667

False Northing: 1,640,416.6667Central Meridian: -116.2500

Standard Parallel 1: 32.7833Standard Parallel 2: 33.8833

Latitude Of Origin: 32.1667Units: Foot US

Ü 0 10 205 Miles

Coordinate System: NAD 1983 StatePlane California VI FIPS 0406 FeetProjection: Lambert Conformal Conic

Datum: North American 1983False Easting: 6,561,666.6667

False Northing: 1,640,416.6667Central Meridian: -116.2500

Standard Parallel 1: 32.7833Standard Parallel 2: 33.8833

Latitude Of Origin: 32.1667Units: Foot US

LegendChanges In NVDIValue

Decrease in NVDI : 1.2381

Increase in NVDI : -1.1828

The false color composite shows a lesser amount of healthy vegetation, leading to drought and higher

susceptibility to fire.

The false color composite shows a major area of

affected burn as well as efforts for growing vegetation.

DISCUSSION

1. While performing the difference in burn ratios for San Diego County the NBR values were calculated for two separate images, one before the fire (2006) and then one after the fire (2008). The NBR is represented by the NIR – SWIR divided by the NIR + the SWIR with each image. Once the images display their own burn ratios a difference in burn ratio are calculated by subtracting the burn ratios of both images. This algorithms output represents an accurate output and signifies the areas that received most burn to areas that received least burn during the 2007 wildfires. The classification as represented in map (1) is based off of the burn ratio index provided by the USGS FireMon program. Areas greater than 0.66 show areas of high severity, values of -0.1 to 0.1 show unburned areas while areas of less than -0.25 show areas of high re-growth.

2. After the burn ratio are classified in a thematic map representation an assessment in the changes of NVDI values are calculated to represent areas of increase and decrease in NVDI for the overall study area. NVDI is calculated for each image by taking the NIR – red color band divided by the NIR + the red color band in each image.

The NVDI values are calculated andThe difference led to NVDI values that were ranging from -1.1828 to 1.2381 (2). This assessment in change detection would indicate that higher values in both directions in the positive and negative values represent areas with most change to vegetation.SUMMARY• Comparative assessment between burn ratios between a pre-fire and post-fire image to calculate a difference in burn ratio representing areas ranging from high to low severity.

• Image analysis between the NVDI between pre-fire and post-fire, with a calculated difference in NVDI values showing the change in vegetation within the burn severity categories.

• The maps of the county of San Diego represents significant change across the landscape as well as correlation between the burn areas and the vegetation index.

ABSTRACT: In this study the county of San Diego California is assessed as an area being subject to the wildfires for the duration of the year 2007. San Diego county was effected by two of the largest fires during the California wildfires and of which covered a vast majority of the county and caused much destruction and damage. The fires had changed most of the vegetation that was pre-existent before the fires ravaged. This project studies the areas that were shown to the greatest amount of change in vegetation as well as provide an accurate measurement of the intensity for these fires in accordance to areas of burn severity. To do this several methods are implored to characterize and display the imagery as there is change detection between post year fire and pre year fire to measure growth in vegetation. The fire itself is measured by utilizing a difference in NBR (Normalized Burn Ratio) and set up into a collective thematic representation. The changes in NVDI (Normalized Difference Vegetation Index) values are accordingly differenced between values from pre year to post year after the fires impact on the landscape. Several models are designed in Erdas imagine to function and output the necessary information for the study area. results

The grey-scale imagery shows the burn ratio for the 2006 date of being acquired.

The grey-scale imagery shows the burn ratio for the 2008 date of being acquired. (notice the areas in black showing areas of burn).

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The study area of San Diego County