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:: Volume 5, Issue 4 (6-2016) ::
JGST 2016, 5(4): 73-84 Back to browse issues page
Evaluation of Groundwater Resources in Iran Using GRACE Gravity Satellite Data
A. Ashrafzadeh Afshar *, Gh. R. Joodaki, M. A. Sharifi
Abstract:   (7905 Views)

Gravity Recovery and Climate Experiment (GRACE) satellite mission has provided a powerful tool to evaluate groundwater resources. In many cases, groundwater resources are nonrenewable, and monitoring the rates at which they are utilized is important for planning purposes. In this study, we have used GRACE level 2 Release 05 data to evaluate groundwater resources across southern Iran (south of 34o latitude) during August 2002 to December 2010. We estimate monthly changes in total water storage (groundwater plus soil moisture plus surface water and snow) across this region using data of GRACE level 2 Release 05, from the Center for Space Research (CSR) at the University of Texas (data available at http://podaac.jpl.nasa.gov). We replace the GRACE results for the degree-one spherical harmonic coefficient, which correspond to geocentre motion due to the Earth’s mass redistribution, with those computed as described by Swenson et al. [2008]. We also replace it for the lowest-degree zonal harmonic coefficient, C20, which is due to the flattening of the Earth, with those obtained from Satellite Laser Ranging (SLR). The effects of Glacial Isostatic Adjustment (GIA) are small in this region, but are nevertheless corrected by a GIA correction model. Stripping effects in the GRACE data, due to the nature of the measurement technique in GRACE and mission geometry, are smoothed by applying a Gaussian smoothing function with a 350 km radius. The results show a large negative trend in total water storage centered over western and southern Iran. GRACE data have no vertical resolution, in the sense that it is impossible to use the GRACE data alone to determine how much of the mass variability comes from surface water or snow, how much comes from water stored in the soil, and how much comes from water in the subsoil layers (i.e., from groundwater). Because our goal is to isolate the changes in groundwater storage, it is necessary to first remove estimates of the other water storage components. Using output from a land surface model such as a version of Community Land Model (CLM4.5) to remove contributions from soil moisture, snow, canopy storage, and river storage, we conclude that most of the long-term water loss in the southern Iran is due to a decline in groundwater storage. Our estimates show that the groundwater loss during this period is at an average rate of 45 km3/yr. We compare our GRACE estimates over southern Iran with Iranian groundwater estimates obtained from 330 active observation wells, used to monitor the level and quality of groundwater across this region. The results show that the conclusion of significant Iranian groundwater loss is further supported by the in situ well data. These estimates represent the combined effects of natural climate variability (e.g., drought) and human activities. Because CLM4.5 also includes unconfined aquifer storage, we can estimate anthropogenic groundwater trends by subtracting the CLM4.5 predictions of naturally occurring groundwater change from our total groundwater change estimates. These results indicate that 2.99 ± 1 km3/yr of the groundwater loss in southern Iran may be attributed to human withdrawals.

Keywords: GRACE Data, Groundwater, Well Data, GLDAS Model, CLM4 Model
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Type of Study: Research | Subject: Geo&Hydro
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Ashrafzadeh Afshar A, Joodaki G R, Sharifi M A. Evaluation of Groundwater Resources in Iran Using GRACE Gravity Satellite Data. JGST 2016; 5 (4) :73-84
URL: http://jgst.issge.ir/article-1-381-en.html

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Volume 5, Issue 4 (6-2016) Back to browse issues page
نشریه علمی علوم و فنون نقشه برداری Journal of Geomatics Science and Technology