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Comparison of Seasonal Terrestrial Water Storage Variations from GRACE with in situ Measurements from the High Plains Aquifer. Gil Strassberg 1 , Bridget Scanlon 1 , Matthew Rodell 2. Bureau of Economic Geology, March 2007. 1 Bureau of Economic Geology

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Comparison of Seasonal Terrestrial Water Storage Variations from GRACE with in situ Measurements from the High Plains Aquifer

Gil Strassberg1, Bridget Scanlon1, Matthew Rodell2

Bureau of Economic Geology, March 2007

1 Bureau of Economic Geology

2 Hydrological Sciences Branch, NASA Goddard Space Flight Center


Outline
Outline from GRACE with in situ Measurements from the High Plains Aquifer

  • GRACE

  • High Plains Aquifer

  • Data and Methods

  • Results


Gravity recovery and climate experiment grace
Gravity Recovery and Climate Experiment (GRACE) from GRACE with in situ Measurements from the High Plains Aquifer

  • Two satellites distance ~ 220km

  • Satellites detect changes in Earth's gravity field by monitoring the changes in distance between the satellites as they orbit Earth.

Launch March 2002

Figures from CSR website:

http://www.csr.utexas.edu/grace/

Distance ~ 220 km


How it works
How it works from GRACE with in situ Measurements from the High Plains Aquifer

The positions of the two GRACE satellites change in response to variations in Earth's gravity field

Lead satellite pulls away due to gravity change

High accuracy device can detect changes within 10 µm

Figures from CSR website:

http://www.csr.utexas.edu/grace/


Can we monitor water storage changes from space

Can we monitor water storage changes from space?

“changes in water mass… should be readily detectable in a region the size of the High Plains aquifer ”

Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and Its Fluid Envelopes (1997).


From gravity to water mass
From gravity to water mass changes

  • GRACE provides time varying global gravity fields (~30 days)

  • Observed monthly changes in gravity are caused by monthly changes in mass

  • Mass changes are mainly attributed to changes in the distribution of water mass in:

    • Hydrologic reservoirs (soil, groundwater, waterbodies, snow)

    • Oceans

    • Atmosphere

    • Cryosphere (frozen)

Figure from GRACE Tellus website:

http://gracetellus.jpl.nasa.gov/


Terrestrial water storage tws
Terrestrial water storage (TWS) changes

Atmospheric mass

Total mass

Terrestrial mass

Total mass = TWS + Atmospheric mass

  • Terrestrial Water Storage includes:

    • Water in reservoirs and rivers

    • Soil moisture

    • Groundwater

    • Snow and Ice

    • Biomass

Estimated from climate models European Center for Medium-Range Weather Forecasts (ECMWF)


Estimating storage changes
Estimating Storage Changes changes

  • GRACE satellites measure monthly gravity changes

  • Gravity changes  Terrestrial Water Storage changes

  • Storage changes in TWS components can be estimated when combined with other data (modeled or measured)

Groundwater storage

Snow water equivalent

Biomass

Terrestrial water storage

Soil moisture

Surface water


Previous studies illinois
Previous studies - Illinois changes

Yeh et al (2006) compared GRACE TWS changes in Illinois (200,000 km2) with monitored soil moisture and groundwater

GRACE TWS

SM + GW + IZ

TWS - SM

GW + IZ


Previous studies greenland ice sheet
Previous studies – Greenland Ice Sheet changes

Chen et al. (2006) showed melting of the ice sheet in East Greenland

Mass changes between April 2002 and November 2005


Previous studies land surface models
Previous studies – Land Surface Models changes

  • TWS data is useful for calibration and validation of land surface models

  • Niu et al. (2006) combined GRACE TWS with modeled subsurface water to compare with modeled snow water equivalent in 4 arctic river basins

  • AMSR = Advanced Microwave Scanning Radiometer

  • Model = NCAR Community Land Surface Model (CLM)


Other studies
Other studies changes

  • GRACE data is used to help monitor and model many large scale processes:

  • Estimation of ET and P-ET over large river basins

  • Continental water cycle and continental ocean discharge

  • Sea level change

  • Water balance in large lakes (e.g. Three-Gorges Reservoir, lake Chad)

  • Climate change

  • Earthquake effects

GRACE data capturing changes in the Earth’s gravity field due to the December 2004 Sumatra earthquake (CRS website: http://www.csr.utexas.edu/GRACE/publications/press/ )


Outline1
Outline changes

  • GRACE

  • High Plains Aquifer

  • Data and Methods

  • Results


High plains aquifer
High Plains Aquifer changes

  • Underlies 8 states in the U.S. (~ 450,000 km2)

  • One of the principal aquifers in the U.S. and one of the major agriculture areas of the world (~ 175,000 km2 cultivated)

  • 27% of irrigated land in the US

  • 30% of the groundwater used for irrigation in the US

  • Highly monitored by Federal and State agencies


Irrigation
Irrigation changes

  • Semi arid conditions (P = 400-700 mm and E = 1500 - 2700 mm)

  • ~50,000 km2 of irrigated area, ~30% of cultivated area)

  • 23.5 km3 (19M acre-feet) of water pumped from the aquifer in 2000, with about 95% withdrawn for irrigation

  • Equivalent to 52 mm of water over the entire aquifer area


Irrigation and water levels
Irrigation and Water Levels changes

  • Water levels and storage have been declining due to irrigation (average 3.8 m and maximum of 68 m)

  • USGS surveys since 1988 – only in winter

  • Good estimate of groundwater storage (~9200 wells monitored in 2003)

Groundwater storage from predevelopment to 2003

million-acre feet

Figure from McGuire (2004):

http://pubs.usgs.gov/fs/2004/3097/


Expected seasonal groundwater signal

Long term trend changes

Expected seasonal groundwater signal

  • ~90% of groundwater pumped during summer (May-August)

  • Water levels recover to a “static” level during winter

  • Expect a seasonal signal in groundwater storage

  • Long term trend of decreasing water storage

Winter

Winter

Groundwater storage

Summer

Summer


Outline2
Outline changes

  • GRACE

  • High Plains Aquifer

  • Data and Methods

  • Results


Estimating groundwater storage changes
Estimating Groundwater Storage Changes changes

Combine GRACE derived Terrestrial Water Storage (TWS) and modeled Soil Moisture (SM) from a land surface model to estimate groundwater changes

Groundwater storage

Snow water equivalent

Biomass

Terrestrial water storage

Soil moisture

Surface water


Terrestrial water storage
Terrestrial Water Storage changes

  • TWS is derived from 3 datasets processed by the GRACE partners.

  • Data represent mass anomalies after taking out atmospheric mass.

  • Data is smoothed with a 400-km Gaussian smoother to isolate the signal.

Maximum TWS anomaly ~ 80 mm

Missing data

mass anomaly (mm)


Soil moisture and tws
Soil Moisture and TWS changes

  • Soil moisture was estimated from the Noah land surface model driven by the North American Land Data Assimilation System (NLDAS).

  • 1/8 degree grid over North America

  • High resolution parameters including hourly observation-based precipitation and solar radiation, and detailed soil and vegetation.

SWE is negligible

mm water


Is swe really negligible
Is SWE really negligible? changes

Drilling near Amarillo


Soil moisture
Soil Moisture changes

  • Soil moisture from 86 sites

  • Seasonal SM changes were calculated for each site

  • Data were averaged on a 1x1 degree grid

  • Estimated overall SM changes

  • Compared to modeled SM anomalies

SM anomaly (mm)


Surface water
Surface water changes

  • Flat terrain, no major reservoirs

  • Internally drained into ephemeral lakes (playas)

  • ~53,000 playas covering ~0.5% of the land surface area

http://www.rw.ttu.edu/torrence/


Surface water1
Surface water changes

Playa area

  • Use 1/3 second (~10m) DEM to estimate playa depths

  • Sample of 130 playas

  • Average depth = 1.06 m

0.5% * 1.06 m = 5.3 mm

Sample area

~1 m

Depth = hmax – hmin

hmax

hmin

Elevation from 1/3 arc second (~10m)


Biomass
Biomass changes

  • Rodell et al. (2005) estimated biomass changes from remotely sensed Leaf Area Index (LAI)

  • Seasonal variations were < 5 mm

Figure form Rodell et al (2005)


Estimating groundwater storage
Estimating Groundwater Storage changes

Assimilated water levels from groundwater databases: USGS NWIS, Texas Water Development Board (TWDB), and Kansas WIZARD groundwater database

2,719 wells with seasonal water level changes

Water level change

between 4-6 2003 and 7-9 2003

Water level changes are calculated per well as differences between seasonal averages


Spatial aggregation of water level changes
Spatial Aggregation of Water Level Changes changes

  • Water level changes were averaged over a 1x1 degree mesh

  • Based on wells with daily water levels we filter out changes > 4.57 m (15 feet)

Water level change

Between 4-6 2003 and 7-9 2003

Spatially aggregated water level changes

Water level change (m)


Variations in groundwater storage
Variations in Groundwater Storage changes

  • Convert water level changes to storage changes (Sy = 0.15)

  • Seasonal cycle with an amplitude of ~ 75 mm

  • Compare to changes (winter to winter) from USGS

Anomalies of groundwater storage

1

2


Outline3
Outline changes

  • GRACE

  • High Plains Aquifer

  • Data and Methods

  • Results


Groundwater storage and soil moisture
Groundwater Storage and Soil Moisture changes

Changes of groundwater and soil moisture are same order of magnitude

Seasonal variation in SM and GWS


Tws vs groundwater storage soil moisture
TWS vs. Groundwater Storage + Soil Moisture changes

  • Seasonal TWS change ranged 8-93 mm, mean = 43 mm

  • Changes winter/spring – summer/fall range 40-100, mean = 75 mm

Estimated the TWS uncertainty between 32-37 mm, mean 34 mm


Groundwater storage vs tws soil moisture
Groundwater Storage vs. TWS - Soil Moisture changes

  • Seasonal TWS-SM change ranged 1-63 mm, mean = 26 mm

  • Changes winter/spring – summer/fall range 30-100, mean = 57 mm

Close to estimated discharges of 52


Detectability of changes
Detectability of changes changes

Mean uncertainty in TWS-SM changes = 49 mm

Detectible:

Uncertainty = 49 < change

Uncertainty estimate might be too conservative and will probably be modified

  • Winter/spring – Summer/fall TWS changes detected 4 out of 5 periods

  • Maximum TWS-SM were detected 3 out of 5 periods


Summary
Summary changes

  • Seasonal changes in TWS in the High Plains aquifer area are due to changes in soil moisture and groundwater storage (surface water, snow water equivalent, and biomass are negligible)

  • GRACE-derived TWS agreed well with SM + GWS (same magnitude, trends, R = 0.82)

  • Variations in groundwater storage from water level measurements showed a fair agreement with TWS – SM (same trend and magnitude, R = 0.58)

  • TWS changes were detectible in 4 out of 5 periods (winter/spring-summer/fall)

  • TWS-SM changes were detectible in 3 out of 5 periods


Future work
Future Work changes

  • Add data for 2006

  • Include new release of GRACE data

  • Add new soil moisture data

  • Spatial variations

  • Improve uncertainty estimate

  • See how this can be applied in other regions

Winter-Spring 2005 SM change

Seasonal SM change (mm)


Questions
Questions? changes


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