Identification of Crop Groundwater and Surface Water Consumption Using Blue and Green Virtual Water Contents at a Subwatershed Scale

Abstract

Large irrigation water withdraws are required where increasing development demands agricultural expansion. In many jurisdictions there is little documentation of agricultural water use, especially groundwater abstraction. Although primarily employed at a national scale, the concept of virtual water is used to calculate regional water-use. The main objective is to analyze watershed-scale crop-specific water consumption to identify local stresses and affected water systems. The 398 km2 quaternary watershed of Whitemans Creek in Ontario, Canada, is evaluated using an approach that can be applied to other locations using often-available data. Virtual water (VW) of major field crops is calculated for 1983, 2011 and 2012, using methods outlined in the FAO and Drainage Paper No. 56. The blue and green VW components are identified. Blue water is specified as ground or surface water, and green water as available soil water. Water consumption results are compared with the regional water budget. For 2011, green and blue VW requirements were 3,540 and 157 L/s, respectively. The blue water, over 80 % sourced from groundwater, was comparable to the 151 L/s agricultural water consumption estimate from the local water budget using general extraction coefficients. With agriculture in the subwatershed using 95 % of the daily permitted blue water takings, identifying high water consumers and their withdrawal sources is important for land-use and water conservation planning. The VW calculations, using real climate data and crop inventory, provide field-scale information that can be applied as alternatives to general crop extraction coefficients.