Agricultural water use estimation using geospatial modeling and a geographic information system

Fresh water resources in the world are limited and, often, disputes occur on how to share them. In many regions, agricultural water use is significant but poorly documented. In order to contribute to solutions for water disputes involving such regions, methodologies need to be developed for regional water use estimation. In this paper we present a case study of Georgia (USA) which is locked in a water dispute with its neighboring states—Alabama and Florida. Agricultural water use in Georgia was essentially unknown because of no reporting requirement. Using a geographic information system and geospatial techniques, the depths of irrigation for cotton, peanut, and maize are estimated for the Flint, Central, and Coastal water zones of Georgia for 2000–2002. The geospatial techniques included the Inverse Distance Weighting, Global Polynomial, Local Polynomial, Radial Basis Function, Ordinary Kriging, and Universal Kriging. The volume of irrigation for these crops was estimated for 2000 and 2001. On the basis of root mean squared error, the Radial Basis Function technique was found to be the most successful one, followed by the Local Polynomial technique. The study of variograms revealed that the depth of irrigation at a site was influenced by its neighboring sites within a radius of about 40 km in the case of cotton, and within about 70 km in the case of peanut. No such influence could be detected for maize. The total volume of irrigation was highest for the Flint zone (564.2 Mm3), followed by the Central zone (291.9 Mm3) and the Coastal zone (94.1 Mm3) for 2000. For 2001, the irrigation volume declined by 40% for the Flint zone, 32% for the Central zone, and 16% for the Coastal zone. The estimates presented in this study can be improved by including more representative sampling sites if possible, by studying the patterns of irrigated lands in Georgia, and by using satellite data for estimating irrigated area for individual crops.