California Drought

Wet Year (2011) vs. Dry Year (2014)

ES 771 Remote Sensing Fall 2014
Kyle Jackson & Calif Tervo

Silver City

Location and Geology:

Silver City lies within the borders of Sequoia National Park in the south central region of California. The park encompases approximately 400,000 acres of of high-elevation forest in the Sierra Nevada mountain range.

Silver City Precipitation

2011: 32.35”
2012: 15.88”
2013: 12.51”
2014: 09.95”

source - CA Dept. of Water Resources

The Sierra Nevada mountain range is primarily composed of granite, diorite and monzonite. The age of the range is approximately 10 million years. Several periods of glaciation caused massive errosion, which has created a high degree of relief within the Sierra Nevada. Some sections of the park also contain metamorphic rocks, such as schist, quartzite and marble. These are the remnants of volcanic islands that occurred before the uplift of the mountain range. Water has erroded the marble, creating a vast network of caves. (Geology Overview)

Vegetation:

Vegetation in the mountainous regions of Sequoia National Park follows an elevation gradient from valley to the timber line. The valley along the edge of the Sierra Nevada is made up of thick-leaved shrubs, chaparral communities, and blue oak savanna with non-native annual grasses. The lower and middle slopes of the Sierra Nevada consist of ponderosa pine, incense-cedar, white fir, sugar pine, and sequoia. Sequoia in this area can grow to over 60 meters (200 feet) in height. (Plants of Sequoia National Park)

The park is home to the largest tree by volume in the world. The tree, dubbed The General Sherman Tree is 83.8 meters(274.9 feet) tall, with a ground circumference of 31.1 meters (102.6 feet) (The General Sherman Tree).

The upper montane regions consist of primarily red fir and lodgepole pine. Diversity in the upper montane regions is limited by winter snow accumulation and dense canopy. The upper edge of the montane forest almost exclusively contain foxtail pine in the southern regions and whitebark pine in the northern regions. (Plants of Sequoia National Park)

Many of the plant species in the region are considered old growth, which means they should be expected to tolerate drought relatively well compared to other species. For example, sequoia trees are among the oldest living trees in the world. Some sequoia live for as long as three thousand years. This would imply that many (if not, most) sequoia trees have likely survived severe and prolonged droughts in the past. It is likely that most of the trees in the community have survived more severe conditions in the past. There is also evidence that sequoia can thrive in drought conditions. During the last major California drought in the 1970s, sequoia growth rates increased possibly due to the demise of other competing plant species. (Oskin)

Some old growth species serve the important purpose of supporting the re-growth of the forest after vegetation is lost to disasters. Whitebark pine seeds provide a food source for seed-eating birds and mammals. In turn, the seed eating animals will provide a mechanism for seed dispersal. Without a food source, many of the birds and mammals would either move on or die of starvation causing slower regrowth. (Forests of Sierra Nevada)

Landsat Imagery

Landsat imagery of the region surrounding Silver City was acquired in september of 2011 and 2014. September was chosen as the last yet year before a three year drought across the state. The time period encompassing this study is intended to provide insight into the effects of the severe drought conditions on vegetation in the study regions. In the following images, Siver city is located in the north central portion of the image. The east fork of the Kaweah river cut a deep canyon in the center of the image. Lost Canyon Creek and Soda Creek flow into Big Arroyo in the north eastern part of the image. The Big Arroyo flows east, eventually spilling into the Kern River. The montane forest areas are mostly found in the western part of the image. The mountains taper toward the western edge of the image, where they gradually drop into the San Juaquin Valley.

2011 Composite 1,2,3 and 2014 Composite 3,4,5:

The September 2011 composite of landsat 7 bands 1,2 and 3 corresponds with the 2014 composite of landsat 8 bands 234. These images approximate natural color. The snowcapped mountains are readily visible on the eastern side of the image with deep river canyons cutting into several areas of the image. The two images show little difference.

2011 Composite 2,3,4 and 2014 Composite 3,4,5:

The September 2011 composite of landsat 7 bands 2,3 and 4 corresponds with the 2014 composite of landsat 8 bands 3,4 and 5. These are false color composite images with the near-infrared bands depicted as red. These two images also show little difference, but the canyon regions show the most difference. The canyon regions appear to show less red in the 2014 imagery, indicating that the drought has possibly affected the vegetation surrounding the rivers. It is also possible that the rivers are carrying less water due to the drought.

2011 Composite 3,4,5 and 2014 Composite 4,5,6:

The September 2011 composite of Landsat 7 bands 3, 4 and 5 corresponds with the 2014 composite of Landsat 8 bands 4,5 and 6. In these images, near infrared band is depicted as green. The red portions of the canyon correspond with the detection of short-wave infrared spectrum (SWIR). This portion of the spectrum is detected by Band 6 in the Landsat 8 data and Band 5 in the Landsat 7 data. SWIR is detected mosre in the 2011 data, especially near the southern part of the river canyon. It is most likely that the SWIR is detecting soil moisture. Much of the soil moisture appears to be gone in the 2014 image, indicating that the drought may have had an effect on this area.

NDVI Images:

Normalized Difference Vegetation Index (NDVI) is a useful method for monitoring photosynthetically active vegetation. The chlorophyll in a plant absorbs visible light from 0.4 to 0.7 microns, while the cell structure of leaves reflect near infrared light from 0.7 to 1.1 microns. The method used for NDVI divides the difference of near-infrared radiation and visible radiation (NIR - VIS) from the sum of near-infrared and visible radiation (NIR + VIS). The result is a number that ranges from -1 to 1. A zero value would indicate no vegetation, while 1 indicates the highest possible density of green. (Measuring Vegetation)

Vegetation Ratios: 2011 Bands 3 and 4 and 2014 Bands 4 and 5:

A simple ratio of visible red and near-infrared bands can be used to analyze the dominance of vegetation within a scene. In this instance the 2011 and 2014 red and near-infrared bands were analyzed for simple vegetation ratios. When looking at the ratio values, there is a recognizable difference between the 2011 and 2014 data. Aside from the rocky areas encompassing the canyons, the 2011 data has relatively uniform vegetative activity. By contrast, the 2014 data shows the highest vegetative activity within the montane forested regions. This reinforces the concept that the region's montane forests maintain a tolerance to drought that the lower plant species do not. However, even the montane forests appear to have lower ratio values in the 2014 data. This indicates that after three years of drought even the hardy trees are affected.

Mid-infrared False Color Composites: 2011 Bands 2,5,7 and 2014 Bands 3,6,7:

Mid-infrared false color composites are useful for depicting a relatively natural color for vegetation, but water and moisture can show up as black or dark blue. In the 2011 image, blue regions are visible surrounding the ponds on the east. These blue are likely to correspond with either moist soils at the edge of the ponds. These blue regions are not aparent in the 2014 image, indicating that the drought has diminished the ponds, and the surrounding soils have dried.

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Spanish Flat

Spanish Flat Precipitation

2011: 53.74”
2012: 22.11”
2013: 20.51”
2014: 20.96”

source - CA Dept. of Water Resources

The Spanish Flat location is east of Jackson and south of Placerville in the Sierra foothills of the Sierra Nevada range lying to the east. The altitude is about 3,000’ – 5,000’. The bedrock is granitic rock. There is pine forest with extensive logging.

Natural Color Composite- Bands 1,2, &3

The visible bands are used in this combination, so ground features appear in colors similar to their natural appearance. The 2011 image is very dark with dark green forested areas and light clear-cut logged patches. The 2014 image is lighter overall and contains more logged areas.

False Color Composite- Bands 2, 3, &4 and NDVI Palette

Healthy vegetation appears green with the darker the green the healthier the vegetation. Clear-cut areas are shades of pink. The 2014 image shows changes in the vegetation. More of the previous dark green is a lighter shade, possibly showing signs of the drought. There are more clear-cut areas. The newer clear-cut areas stand out in bright pink. The older logged areas are more subdues pink, perhaps showing some vegetation cover.

NDVI Images - Bands 3 & 4

The Normalized Difference Vegetation Index (NDVI) is an index of plant “greenness” or photosynthetic activity, and is one of the most commonly used vegetation indices, because the normalized difference between the red and near infrared bands is very sensitive to total plant cover, biomass, plant and soil moisture, and plant stress. One could think the images are reversed as the 2014 image is darker green. We can not account for this except to note the 2014 is more saturated in color. In the 2014 image, the freshly logged areas are very red.

NDVI False Color- Bands 3 & 4

The 2014 image contains much more pink and red indicating thinner or no vegetation. The newer logging is very red. Much of the green in 2014 looks dirty indicating thinner or less healthy biomass.

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Santa Cruz

Santa Cruz Mountains Rainfall

2011: 57.17”
2012: 30.43”
2013: 34.45”
2014: 19.65”

source - CA Dept. of Water Resources

The Santa Cruz Mountains are located just north of Santa Cruz, California. The altitude varies from 800’ to about 4,000’. They are part of the Pacific Coast Ranges have a Mediterranean type climate with slightly more coastal drizzle and fog. The mountains are well forested including redwoods and pine

Natural Color Composite- Bands 1, 2, & 3

The visible bands are used in this combination, so ground features appear in colors similar to their natural appearance. The greens in the 2014 image may be slightly lighter in color indicating less health vegetation.

False Color Composite- Bands 2, 3, & 4

In false color composite healthy vegetation appears magenta. These images appear very similar.

NDVI Images - Bands 3 & 4

The Normalized Difference Vegetation Index (NDVI) is an index of plant “greenness” or photosynthetic activity, and is one of the most commonly used vegetation indices, because the normalized difference between the red and near infrared bands is very sensitive to total plant cover, biomass, plant and soil moisture, and plant stress. The 2011 image has noticeably more dark green vegetation than the 2014 image. The 2014 image has lighter green and mottled green, indicating the stress of the drought.

NDVI False Color- Bands 3 & 4

We thought we would see a bigger difference between these images because NDVI is a good indicator of plant stress. In 2014, some of the pinkish area appear slightly larger and more pronounced.

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