Climate change-induced variations in blue and green water usage in U.S. urban agriculture

Urban agriculture could assist in meeting the growing global demand for food without overburdening agricultural areas. To fully realize the potential of urban agriculture, it is necessary to better understand the implications of urban agriculture and climate change on the food-energy-water nexus. The objective of this study was to investigate the influence of local climate change on irrigation requirements, and green and blue water usages for turf grass and three common urban agriculture crops (carrots, spinach, and sweet corn) in eight mid-sized U.S. cities. Baseline (1980–2010) and Future (2040–2050) daily climate data were combined with site-specific crop water uptake data to calculate irrigation requirements using the Irrigation Management System Model, IManSys, a numerical simulation model that uses a water balance approach. The irrigation requirements (IRRs) were further used to calculate the energy requirements and associated greenhouse gas emissions for the four crops in each location. Results showed the spatio-temporal impact of climate change on precipitation and evapotranspiration and consequently on crop IRRs. On the east coast, increases in summer precipitation during the crop growing seasons result in relatively small increases in blue water contributions (<222%) to crop water demands. On the west coast, though, decreases in precipitation lead to more drastic increases in blue water contributions (>222%) for these same crops. The energy requirements and greenhouse gas footprints of urban agriculture were weakly correlated to the blue water portion of the IRRs in individual cities but were largely impacted by the source of the water used. Overall, the results highlight the importance of appropriate and thoughtful crop selection for urban agriculture paired with environmentally sustainable water sourcing to maintain, or even reduce, future water and energy footprints of urban agriculture.