Global crop output and irrigation water requirements under a changing climate

The anthropogenic increases in CO2 atmospheric concentrations are expected to lead to multiple and possibly opposing effects on crop performance with important implications for crop water productivity. The study integrates the global responses to mounting concentrations at three levels - climatic, cropping and economic - to determine the deviations in crop production and irrigation water requirements from a 'no climate change' socioeconomic development storyline. The biophysical effects are considered comprehensively for eight crop classes by taking into account alterations both to rainfed and irrigation yields, and to irrigation water intensities. These changes in crop growing conditions are explored in the 2004-2050 timeframe across two concentrations pathways (RCP2.6 and RCP 8.5) with the inclusion of the CO2 fertilisation effect. The economic responses are determined through a global water CGE model (RESCU-Water) comprising a bottom-up representation of crop systems. Changes in climatic conditions reduce crop output and depress the global water demand for irrigated crops in spite of an increase in irrigation water intensities. Discrepancies in crop production impacts between tropical and temperate regions increase with CO2 concentration levels. Embedding CO2 fertilisation more than offsets these adverse effects by determining a net increase in crop production and a reduction in irrigation water requirements at a regional level. The resulting water savings potential, even in the lower concentrations scenario (RCP2.6), warrant more research with the aim of reducing the different classes of uncertainty regarding the effects of CO2 fertilisation.