Abstract
Water is a major factor limiting crop production in many regions around the world. Irrigation can greatly enhance crop yields, but the local availability and timing of freshwater resources constrains the ability of humanity to increase food production. Innovations in irrigation infrastructure have allowed humanity to utilize previously inaccessible water resources, enhancing water withdrawals for agriculture while increasing pressure on environmental flows and other human uses. While substantial additional water will be required to support future food production, it is not clear whether and where freshwater availability is sufficient to sustainably close the yield gap in cultivated lands. The extent to which irrigation can be expanded within presently rainfed cropland without depleting environmental flows remains poorly understood. Here we perform a spatially explicit biophysical assessment of global consumptive water use for crop production under current and maximum attainable yield scenarios assuming current cropping practices. We then compare these present and anticipated water consumptions to local water availability to examine potential changes in water scarcity. We find that global water consumption for irrigation could sustainably increase by 48% (408 km3 H2O yr−1)—expanding irrigation to 26% of currently rainfed cultivated lands (2.67 × 106 km2) and producing 37% (3.38 × 1015 kcal yr−1) more calories, enough to feed an additional 2.8 billion people. If current unsustainable blue water consumption (336 km3 yr−1) and production (1.19 × 1015 kcal yr−1) practices were eliminated, a sustainable irrigation expansion and intensification would still enable a 24% increase in calorie (2.19 × 1015 kcal yr−1) production. Collectively, these results show that the sustainable expansion and intensification of irrigation in selected croplands could contribute substantially to achieving food security and environmental goals in tandem in the coming decades.
Highlights
Steady increases in crop production have supported marked population growth while substantially reducing incidences of malnourishment globally (Pingali 2012)
Our assessment shows that 40% of this volume of irrigation water is currently consumed at the expense of environmental flows (Jägermeyr et al 2017) or groundwater stocks
This study investigated the extent to which irrigation can be expanded within presently rainfed cultivated lands without depleting environmental flows
Summary
Steady increases in crop production have supported marked population growth while substantially reducing incidences of malnourishment globally (Pingali 2012). This Green Revolution was made possible through the proliferation of high-yielding crop varieties, increased pressures on land and water, substantial nutrient inputs, and rising greenhouse gas emissions, making agriculture one of humanity’s most profound environmental burdens. While water and other inputs will likely be used more efficiently under higher yields (i.e., more crop per drop), additional irrigation will be needed in many places in order to close the yield gap and to maximize food production (Gerten et al 2011, Tilman et al 2011, Pfister et al 2011, Mueller et al 2012, Davis et al 2017a)
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