Angus I. Calderhead

Groundwater depletion in Central Mexico: Use of GRACE and InSAR to support water resources management

Groundwater deficits occur in several areas of Central Mexico, where water resource assessment is limited by the availability and reliability of field data. In this context, GRACE and InSAR are used to remotely assess groundwater storage loss in one of Mexicos most important watersheds in terms of size and economic activity: the Lerma-Santiago-Pacifico (LSP). In situ data and Land Surface Models are used to subtract soil moisture and surface water storage changes from the total water storage change measured by GRACE satellites. As a result, groundwater mass change time-series are obtained for a 12 years period. ALOS-PALSAR images acquired from 2007 to 2011 were processed using the SBAS-InSAR algorithm to reveal areas subject to ground motion related to groundwater over-exploitation. In the perspective of providing guidance for groundwater management, GRACE and InSAR observations are compared with official water budgets and field observations. InSAR-derived subsidence mapping generally agrees well with official water budgets, and shows that deficits occur mainly in cities and irrigated agricultural areas. GRACE does not entirely detect the significant groundwater losses largely reported by official water budgets, literature and InSAR observations. The difference is interpreted as returns of wastewater to the groundwater flow systems, which limits the watershed scale groundwater depletion but suggests major impacts on groundwater quality. This phenomenon is enhanced by ground fracturing as noticed in the field. Studying the fate of the extracted groundwater is essential when comparing GRACE data with higher resolution observations, and particularly in the perspective of further InSAR/GRACE combination in hydrogeology.

C-band D-InSAR and field data for calibrating a groundwater flow and land subsidence model

Differential Synthetic Aperture Radar Interferometry (D-InSAR) is a powerful technique used for detecting and measuring surface deformation with sub-centimetre accuracy. Using C-band data from three different satellites, the D-InSAR technique is used to calibrate a coupled groundwater flow and land subsidence numerical model. Additionally, D-InSAR results from different sensors are compared and contrasted. When comparing D-InSAR results with extensometers and water levels, a direct correlation is nociced. For all D-InSAR image pairs, large baselines, atmospheric effects, temporal decorrelation, and vegetative cover were limiting factors in obtaining a maximum number of usable interferograms. The total maximum subsidence for a point location in the valley between November 2003 and May 2008 is approximately 40 cm reaching a maximum total subsidence of over 2.0 metres since 1962. When contrasting the ENVISAT ASAR and RADARSAT-1 data, subsidence rates were similar yet the distribution had significant differences. Additionally, ENVISATs shorter baselines led to more accurate results.

Groundwater deficit and land subsidence in central mexico monitored by grace and RADARSAT-2

In the context of a lack of reliable data in assessing groundwater overexploitation, space borne sensors bring useful information. While space-borne SAR and gravimetric data are now used to study groundwater, their interoperability is still poorly studied. In this paper, we apply two cutting-edge techniques for the deficit assessment of one of Mexicos most important watersheds. Space-borne gravimetry is used to extract total and groundwater storage variations from 2003 to 2013 meanwhile InSAR techniques allow the detection of groundwater deficit areas in 2012 and 2013. GRACE reveals the large-scale combined effect of local unconfined aquifer overexploitation revealed by InSAR. Results show a non-anthropogenic water deficit within the northern half of the basin. Important local decreases in groundwater storage are observed by InSAR within several cities of the southern part of the basin, but groundwater storage loss is partially compensated by surface water storage increase.