Spatial Quantification of Groundwater Abstraction in the Irrigated Indus Basin by M.J.M. Cheema 1,2 , W.W. Immerzeel 3,4 , and W.G.M. Bastiaanssen 5,6 Abstract Groundwater abstraction and depletion were assessed at a 1-km resolution in the irrigated areas of the Indus Basin using remotely sensed evapotranspiration (ET) and precipitation; a process-based hydrological model and spatial information on canal water supplies. A calibrated Soil and Water Assessment Tool (SWAT) model was used to derive total annual irrigation applied in the irrigated areas of the basin during the year 2007. The SWAT model was parameterized by station corrected precipitation data (R) from the Tropical Rainfall Monitoring Mission, land use, soil type, and outlet locations. The model was calibrated using a new approach based on spatially distributed ET fields derived from different satellite sensors. The calibration results were satisfactory and strong improvements were obtained in the Nash-Sutcliffe criterion (0.52 to 0.93), bias (−17.3% to −0.4%), and the Pearson correlation coefficient (0.78 to 0.93). Satellite information on R and ET was then combined with model results of surface runoff, drainage, and percolation to derive groundwater abstraction and depletion at a nominal resolution of 1 km. It was estimated that in 2007, 68 km 3 (262 mm) of groundwater was abstracted in the Indus Basin while 31 km 3 (121 mm) was depleted. The mean error was 41 mm/year and 62 mm/year at 50% and 70% probability of exceedance, respectively. Pakistani and Indian Punjab and Haryana were the most vulnerable areas to groundwater depletion and strong measures are required to maintain aquifer sustainability. Introduction Quantification of groundwater abstraction, especially in arid regions where recharge is genuinely small, is of prime importance for sustainable basin scale water 1 Department of Irrigation and Drainage, University of Agriculture, Fasialabad, Pakistan. 2 Corresponding author: Water Management Department, Delft University of Technology, Stevinweg 1, 2628 CN Delft, The Netherlands; 31-15-2785074; mjm.cheema@gmail.com 3 Future Water, Costerweg 1G, 6702 AA Wageningen, The Netherlands. 4 Department of Physical Geography, University of Utrecht, Utrecht, The Netherlands. 5 Water Management Department, Delft University of Technology, Stevinweg 1, 2628 CN Delft, The Netherlands. 6 eLEAF Competence Center, Generaal Foulkesweg 28, 6703 BS Wageningen, The Netherlands. Received April 2012, accepted January 2013.  2013, National Ground Water Association. doi: 10.1111/gwat.12027 resources. Long-term groundwater abstractions should not increase than the recharge but rapid population growth and increased irrigation development for food security has resulted in exhaustive groundwater abstractions in many alluvial plains (Foster and Chilton 2003; Shah et al. 2007). Siebert et al. (2010) developed a global inventory on groundwater which estimated that 43% of the total con- sumptive irrigation water use met through groundwater. Groundwater abstractions are temporally episodic and spa- tially variable and depend upon the crop irrigation needs, surface water availability, and water quality. The spatial variability in groundwater availability and water require- ment by crops complicate the quantification of abstrac- tions. The Indus Basin is a typical example showing high variability in land use, climate, canal water availability, soil types, and irrigation practices without any regulation in place to measure the groundwater abstraction. In the Indus Basin, groundwater is utilized solely or in conjunction with surface water to augment insufficient NGWA.org Vol. 52, No. 1 – Groundwater – January-February 2014 (pages 25 – 36) 25