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3.9 IUKWC Workshop Freshwater EO - Helen Bonsor - Jun17

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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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3.9 IUKWC Workshop Freshwater EO - Helen Bonsor - Jun17

  1. 1. © NERC All rights reserved Helen Bonsor, Alan MacDonald, Murray Lark, Kay Smith, Laurent Longuevergne Application of GRACE data to understand groundwater resources – examples from Africa and SE Asia
  2. 2. © NERC All rights reserved 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 ?
  3. 3. © NERC All rights reserved 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
  4. 4. © NERC All rights reserved Groundwater Community Rodell: Nature 2009
  5. 5. © NERC All rights reserved African Basins – based on geology African groundwater basins – dynamics and long- term trends
  6. 6. © NERC All rights reserved 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
  7. 7. © NERC All rights reserved Global / continental models…
  8. 8. © NERC All rights reserved Statistical results
  9. 9. © NERC All rights reserved TWS and rainfall
  10. 10. © NERC All rights reserved Long term trends 10 km3 2 km3
  11. 11. © NERC All rights reserved 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
  12. 12. © NERC All rights reserved TWS and annual recharge
  13. 13. © NERC All rights reserved Does it make sense? • Compare to recharge studies • Occasional gw level fluctuations • Sahelian Paradox • Land use patters
  14. 14. © NERC All rights reserved 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
  15. 15. © NERC All rights reserved 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)
  16. 16. © NERC All rights reserved Long term hydrographs Long term history of accumulation Canal leakage since 1850s led to groundwater rise and salinization MacDonald et al. (2016) Nature Geoscience
  17. 17. © NERC All rights reserved 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
  18. 18. © NERC All rights reserved 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.
  19. 19. © NERC All rights reserved 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)

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