The planetary boundaries of freshwater are likely to be exceeded in the near future . At present, the vast majority of water is used for food production. The combination of dietary changes, population growth, and climate change will have major implications for the food supply and for water use in agriculture. In this research, we have created a link between water availability including environmental flow requirements (EFRs) at monthly time step using the global biomass optimization GLOBIOM model  to constrain irrigation supply at a global scale. Water availability is simulated with the global vegetation model LPJml and EFRs are calculated with the Variable Monthly Flow method . Simulations were run under different conditions of climate change and land use change to predict future food production to 2050. This research aims to compare the spatial allocation of global agricultural lands from scenarios, including water availability and EFRs, with socio-economic optimization. By combining biophysical and socioeconomic constrains, sustainable scenarios of agricultural land allocation and irrigation expansion can be simulated including intra-annual variability.
Harmonization of spatial resolution for water availability, EFRs, and water withdrawals for irrigation and other users, such as household and industry, was performed to fit the GLOBIOM model. Data were aggregated to the LUID unit of GLOBIOM (2’ by 2’deg). Water availability and EFRs were recalculated according to the discharge and repartition of EFRs in each watershed . Irrigation coefficient was performed at monthly time step and at grid cell level to represent the seasonality of irrigation demand from LPJml to adapt the irrigation demand from the GLOBIOM model from annual to monthly time step. Irrigation supply was constrained as if water demand for irrigation and other use falls below water availability, crop yield will turn from potential to rain-fed. To predict water availability and water demand in 2050, we used climate radiative forcing input RCP8.5 to represent the impact of climate change and the socioeconomic scenario (SSP2) to predict water demand until 2050.
Figure 1. Discharge change in 2050 (left); WSI including irrigation (right) (click on the image to enlarge).
By including environmental flow as an additional water user, we looked at the water stress index (WSI) which is the ratio of water demand to water availability, and we can conclude that in 2000, Middle East regions, southwest Asia, and the west coast of North America are above the limit of water stress (40%). By 2050 water demand from irrigation and other users is tripled; it is likely to be exacerbated by climate change and increased water stress to be felt in certain regions such as the Mediterranean Basin.
 Gerten D et al. (2013). Towards a revised planetary boundary for consumptive freshwater use: role of environmental flow requirements. Current Opinion in Environmental Sustainability.
 Havlík P et al. (2011). Global land-use implications of first and second generation biofuel targets. Energy Policy 39(10), 5690-5702.
 Pastor AV et al. (2013). Accounting for environmental flow requirements in global water assessments. Hydrol. Earth Syst. Sci. Discuss. 10(12), 4987-15032.
 Gerten D et al. (2011). Global water availability and requirements for future food production. Journal of Hydrometeorology 12(5), 885-899.
Petr Havlik and Amanda Palazzo, Ecosystems Services and Management, IIASA
Amandine Pastor of the Earth System Science Group, Wageningen University, Netherlands, is a French citizen. She was funded by IIASA’s National Member Organization for the Netherlands and worked in the Ecosystems Services and Management (ESM) Program during the YSSP.
Please note these Proceedings have received limited or no review from supervisors and IIASA program directors, and the views and results expressed therein do not necessarily represent IIASA, its National Member Organizations, or other organizations supporting the work.
Last edited: 29 September 2015
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