Global Irrigation Water Demand: Variability and Uncertainties Arising from Agricultural and Climate Data Sets
Dominik
Wisser, University of New Hampshire, dominik.wisser@unh.edu
Steve
Frolking, University of New Hampshire, steve.frolking@unh.edu
(Presenting)
Ellen
Douglas, U. Mass Boston, ellen.douglas@umb.edu
Balazs
Fekete, University of New Hampshire, balazs.fekete@unh.edu
Charles
Vorosmarty, University of New Hampshire, charles.vorosmarty@unh.edu
Andreas
Schumann, Ruhr-University Bochum, Germany, andreas.schumann@ruhr-uni-bochum.de
Water withdrawals for agriculture account for around 80% of the total water that is withdrawn from surface water and groundwater. FAO (2002) projects that irrigated areas in developing countries will continue to grow at an annual rate of 0.6%, representing a decline in per-capita irrigated areas. We use a new irrigation water balance model (WBMplus) to estimate variability and uncertainties arising from agricultural and climate data sets. The variability we assess arises from interannual variability in weather, using two ~50 year reconstructions of global daily weather. We do not account for variability or trends in irrigation area or cropping, but use a contemporary map (so we do not generate an irrigation water use history). The uncertainties come from how well we can know several important factors: the location and extent of irrigation (we use two different global maps), the actual weather (the two reconstructions), soil properties, crop types that are irrigated, and growing/irrigation season timing. Simulated global irrigation water use varied by about 30%, depending on choice of irrigation map or choice of weather data. The combined effect of irrigation map and weather data generated a global irrigation water use range of 2200 to 3900 km3 y-1. Weather driven variability was generally less than ±100 km3 y-1, globally, but could be as large as ±30% at the national scale.
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