Abstract
The Northwest India Aquifer (NWIA) has been shown to have the highest groundwater depletion (GWD) rate globally, threatening crop production and sustainability of groundwater resources. Gravity Recovery and Climate Experiment (GRACE) satellites have been emerging as a powerful tool to evaluate GWD with ancillary data. Accurate GWD estimation is, however, challenging because of uncertainties in GRACE data processing. We evaluated GWD rates over the NWIA using a variety of approaches, including newly developed constrained forward modeling resulting in a GWD rate of 3.1 ± 0.1 cm/a (or 14 ± 0.4 km3/a) for Jan 2005–Dec 2010, consistent with the GWD rate (2.8 cm/a or 12.3 km3/a) from groundwater-level monitoring data. Published studies (e.g., 4 ± 1 cm/a or 18 ± 4.4 km3/a) may overestimate GWD over this region. This study highlights uncertainties in GWD estimates and the importance of incorporating a priori information to refine spatial patterns of GRACE signals that could be more useful in groundwater resource management and need to be paid more attention in future studies.
Highlights
Groundwater is a valuable resource for sustaining agricultural, industrial, and domestic water use in many arid and semi-arid regions globally[1]
We use the three-state region (i.e., Punjab, Haryana & Delhi, and Rajasthan with a total area of 438,296 km[2], the same as Rodell et al.16) in the Northwest India Aquifer (NWIA) as a test-bed, with ~30% of the study region equipped for irrigation (Fig. 1(a)) and 74% of the equipped area irrigated with groundwater (Fig. 1(b) and Supporting Information 2)
Our estimate of groundwater depletion (GWD) from constrained forward modeling for the three-state region during the five-year period Aug 2003 through Oct 2008 is 2.5 ± 0.1 cm/a, which is less than the estimate of 4 ± 1 cm/a for the period Aug 2002 through Oct 2008 by Rodell et al.[16]
Summary
Groundwater is a valuable resource for sustaining agricultural, industrial, and domestic water use in many arid and semi-arid regions globally[1]. Negative environmental impacts of GWD include decreased baseflow that may lead to drying-up of wetlands and rivers, land subsidence, saltwater intrusion, increasing pumping costs, and declining water supplies for some of the world agricultural areas putting sustained crop production at risk[4]. Accurate monitoring of both the rate and spatial pattern of GWD is imperative to formulate reasonable policies to achieve the goals of maintaining agricultural production and sustainable groundwater resources management[5,6]. This makes it imperative to compare GRACE-based GWD with ground-based data to assess their validity; published studies on GRACE-based GWD estimates in the NWIA have not been compared with detailed ground-based monitoring data
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