CO2‐Induced Climatic Changes and Irrigation‐Water Requirements

Effects of CO2‐induced climatic changes on irrigation‐water requirements (IR) in the Great Plains region were evaluated using results of global atmospheric‐circulation models with a water balance‐IR model. Increases were predicted for evapotranspiration Et due to predicted increases in air temperature, solar radiation, and wind speed under doubled concentrations of atmospheric carbon dioxide (2×CO2). Predicted increases in humidity under the 2×CO2 scenarios and shifting of crop life cycles to months with lower levels of solar radiation moderated predicted increases in Et. Increases in irrigation requirements were caused primarily by increases in evaporative demands and changes in precipitation patterns. Increases in net seasonal IR for alfalfa were larger due to predicted increases in length of frost‐free growing seasons and higher evaporative demands as compared to winter wheat and corn. Decreases or only modest increases in seasonal irrigation requirements were projected under 2×CO2 scenarios for com and winter wheat due to reductions in length of crop life cycles and projected increases in bulk stomatal resistances.