Application of GRACE data, and other earth observation datasets, to understand groundwater resources – examples from Africa and SE Asia. Helen Bonsor (BGS)

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Helen Bonsor, Alan
MacDonald, Murray
Lark, Kay Smith,
Laurent Longuevergne
Application of GRACE data to understand
groundwater resources – examples from Africa
and SE Asia

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Growing interest in changes in groundwater storage
Concerns of sustainability – but loose definitions (see Foster in HJ)
Lack of direct observations, lots of models – a perfect storm !
Why bother ?

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GRACE satellites
Twin satellites launched
March 2002, measuring
the geoid
Monthly changes in gravity
to 2 – 4 mGals
Footprint of 400 x 400km
Relates to water mass
change Tapley et al. Science 2004

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Groundwater Community
Rodell: Nature 2009

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African Basins – based on geology
African groundwater basins – dynamics and long-
term trends

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Datasets used
Total water storage from Grace
(CSR release 04)
Rainfall data from NASA TRMM
Soil Moisture from NOAH land
model of GLDAS – but only used
top 3 layers
∆GWS = ∆TWS – ∆SMS, where ∆SMS (above
ZFP)
Statistical approach – empirical
temporal variograms, linear mixed
models

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Global / continental models…

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Statistical results

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TWS and rainfall

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Long term trends
10 km3
2 km3

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Estimating groundwater component
Using upper 3 layers of NOAH GLDAS, related - but does
not explain all variance
Groundwater 24-45% of annual TWS in southern basins
Groundwater 55-78% of annual TWS in northern basins
Importance of different land uses

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TWS and annual recharge

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Does it make sense? • Compare to
recharge studies
• Occasional gw level
fluctuations
• Sahelian Paradox
• Land use patters

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Africa Summary
GRACE, TRMM and GLDAS useful for
characterising storage changes in basins
North African Basins and Karoo, Somalia show
lack of periodicity,
Sahelian basins show periodicity and
estimated significant recharge
Central and southern basins, periodicity but
less recharge
Groundwater accumulation observed, but no
significant regional depletion

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1. Recharge from rainfall,
canals and rivers
2. Significant rainfall gradient
3. Abstraction high – 205 km3
25% global abstraction;
4. GW storage 30,000 km3
20 times the annual flow in
the GMB + Indus, 100 x
storage in dams
5. Yields > 20 l/s often high
6. Large systematic variations
in aquifer: permeability,
storage and anisotropy
IGB groundwater resource – complex, highly
abstracted system
Bonsor et al. Hydrogeol J. (submitted)

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Long term hydrographs
Long term history of accumulation
Canal leakage since 1850s led to
groundwater rise and salinization
MacDonald et al. (2016) Nature Geoscience

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Groundwater depletion – insitu monitoring
data
Water table is near stable across 70%
of the aquifer, falling in 33%
Complex pattern influenced by rainfall,
canals, abstraction
Net depletion of 8 km3per annum
MacDonald et al. (2016) Nature Geoscience

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Comparisons with Grace
MacDonald et al. (2016) Nature Geoscience Supplementary Material
Grace dominated by depletion in Rajasthan Desert
Depletion in the main IGB aquifer is poorly resolved
Rodell et al. Tiwari et al. Chen et al. Panda et al.

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Summary
GRACE, TRMM and GLDAS useful for
characterising storage changes in basins
Consistent, discrete basin responses can be
characterised
Statistical approach to interpret GRACE data
useful and additive to LSM analyses
In situ data essential to interpret GRACE data
at fine resolution (Scanlon, and IGB)