1. Delineation of Groundwater Dependent Ecosystems based on
NDVI Variations in the Dry Season
Keisha Baxter1, Isabel Perez2, Dr. Nir Krakauer2
1 LaGuardia Community College, 2The City College of New York
INTRODUCTION
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Groundwater is a vital source of water throughout many parts of the world making up
98% of the Earth's available freshwater [1]. It can be extracted and used by
communities, plants, mining, and aquatic life. In fact, there are entire ecosystems that
depend on groundwater for their survival these include wetlands, swamps, springs,
coastal mangroves, and some terrestrial vegetation (phreatophytes) [2].
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Increasing use of groundwater by humans has lessened the amount of water available
to the ecosystems which depend on it for their survival. Due to this groundwater
usage imbalance, measures are being established to protect these groundwater
dependent ecosystems (GDEs) by identifying and mapping their location throughout
the study area.
!
These maps will be useful to further serve as a guide for water resources allocators
and managers so they are cautious of the areas they choose to develop and extract
groundwater from, to not cause disturbance to an area which strongly depends on
groundwater. This is analyzed from Normalized
Vegetation Difference Index (NDVI), which shows the greenness of vegetation over an
area.
ABSTRACT
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The purpose of this research is to identify and map areas in south central Texas that
shows high potential for Groundwater Dependent Ecosystems (GDEs). A GDE is an
biological life that may be accessing groundwater i.e. water below the earth’s surface
that is stored in an aquifer.
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To identify these GDEs, two types of analyses were conducted.
1) Seasonal Analysis
2) Inter-Annual Analysis
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The analyses yielded two NDVI images each which were subtracted. The difference
NDVI pixels determined whether the area could be classified GDE or non GDE. K-
means unsupervised classification was used to define the thresholds for the groups.
The inter-annual analysis showed that there is a great deal of locations that have
potential to be accessing groundwater in the area.
SITE STUDY
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The study area is located in south-central Texas, about 30 miles from San Antonio, on
the Edwards Plateau, at the geographical coordinate 29.85˚N and 98.48˚W. With
those coordinates at the center, the range of study extended over a 1.2 km2 area that
includes Honey Creek State Natural Area, Guadalupe River State Park, and Beek
Spring. The Plateau extends west to the Pecos River, about 250 miles west of Austin.
METHODOLOGY
Inter Annual Analysis
• The images for this analysis were
chosen using Palmer Drought
Severity Index (PDSI) which
highlighted the wettest and driest
year.
!
• These years were chosen and
compared for analysis; a difference
NDVI image was obtained and
analyzed for GDEs
Seasonal Analysis
• To select the dates for analysis,
precipitation (PPT) based approach was
used to identify the years of the highest
and lowest PPT value within a dry season
from 2000 to 2012.
!
• The consecutive months with the largest
difference were chosen to be compared
individually as well as the resulting
difference NDVI images of the two.
K-Means Clustering was used to classify difference NDVI as GDE, non GDE and
partial GDEs. These clusters are identified in Figures labeled K-means
Clustering.
CONCLUSIONS AND FUTURE WORK
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This research has shown that there is a great deal of locations that have
potential to be accessing groundwater. Extreme case testing, which was
the method that results were based upon, also showed that within the 1.2
km2 location that consists of Honey Creek State National Park has high
results of GDEs. Ground based research has proven that the area has
GDEs and remote sensing has provided the same results, showing the
efficiency of the tool and satellites. This research will be furthered with
analysis using an average of all the years in the 2000 to 2012 time series
and creating a map of location of GDEs, and analysis of the partial GDE
location will identify why they have a potential to be accessing
groundwater. Also research will be continued to find GDE in other
location throughout the USA.
ACKNOWLEDGEMENTS
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1.This project was made possible by the Research Experiences for
Undergraduates (REU) in Satellite and Ground-Based Remote Sensing at
CREST_2 program.
!
2.The National Oceanic and Atmospheric Administration – Cooperative
Remote Sensing Science and Technology Center (NOAA-CREST) for
supporting this project.
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3.This research is supported by the National Science Foundation's
Research Experiences for Undergraduates (NSF REU) under Dr. Reginald
Blake, Dr. Janet Liou-Mark, Ms. Laura Yuen-Lau.
!
4.My mentors Dr. Nir Krakauer and Isabel Perez for their patience,
guidance and supportive mentorship throughout this research.
REFERENCES
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[1] Commission, N. W. (2012). Groundwater Essentials (pp. 7–37).
Canberra ACT: National Water Commission.
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[2] Fowler, N. (2005). An Introduction to the Vegetation and Ecology of
the Eastern Edwards Plateau (Hill Country) of Texas. Retrieved from http://
www.sbs.utexas.edu/fowler/generalinfo/epveg/epgeol.htm
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[3]Cure, S.(2014). Texas Plant Life. Retrieved from http://
www.texasalmanac.com
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NDVI COMPARISON -SEASONAL ANALYSIS
INTER-ANNUAL COMPARISON OF NDVI
DIFFERENCE NDVI
FIGURES AND GRAPHS
K-MEANS CLUSTERING OF INTER-ANNUAL ANALYSIS
DIFFERENCE NDVI
DISCUSSION
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The inter-annual analysis provides a map of pixels referring to locations, of
the NDVI value for each of the 400 pixels based on the years that had the
highest and lowest Palmer Drought Severity Index (PDSI). K-means
clustering separated the 400 NDVI difference values into 2 distinct groups
labeled high potential for Groundwater Dependence and low potential of
Groundwater Dependence. Here K-means was used as an unsupervised
classification method that statistically defines the threshold for each pixel
as low and high potential to be GDEs.
VEGETATION AND TERRAIN - TEXAS
Precipitation of Study Area in Texas from 2000 to 2012
PrecipitationValue(mm)
0
100
200
300
400
500
TIME (Month- Year)
Apr-00
Aug-00
Apr-01
Aug-01
Apr-02
Aug-02
Apr-03
Aug-03
Apr-04
Aug-04
Apr-05
Aug-05
Apr-06
Aug-06
Apr-07
Aug-07
Apr-08
Aug-08
Apr-09
Aug-09
Apr-10
Aug-10
Apr-11
Aug-11
Apr-12
Aug-12
LOW
Figure -Hydrological Cycle and The effect of Root Depth on Groundwater
Groundwater areas mapped against map of the study
area
HIGH
RESULTS
The seasonal analysis was show to be inappropriate for this study due to soil moisture
being present from the previous month. Inter-annual analysis showed that the areas in mid
to lower part of the study area are have high potential to be accessing groundwater.