Green, Blue and Grey Bioenergy Water Footprints, a Comparison of Feedstocks for Bioenergy Supply in 2040

Today, traditional biomass contributes 75% to total bioenergy use, but the share of modern biomass, e.g., for biofuels or electricity, increases. Bioenergy derives from first (food crops), second (energy crops or agricultural residues) and third (algae) generation feedstocks. There is an ongoing debate about the competition between energy and food crops. Energy crops do not compete with food directly, but indirectly, using the same natural resources like freshwater. Instead of food or energy crops, crop residues can also be used for bioenergy supply. This paper uses the water footprint (WF) concept and compares WFs of first, second and third generation bioenergy (m3/GJ). Next, it compares WFs of future bioenergy demand based on different bioenergy feedstocks. WFs of energy from residues is smallest, WFs of energy crops largest. Bioenergy from algae has the largest blue WF (surface and groundwater). From a resource-use perspective, environmental impacts of green WFs (precipitation) are smaller than impacts of blue WFs. If bioenergy production rises, impacts on freshwater also go up. Increased production of first generation biofuels and energy crops contributes to global water scarcity. Third generation bioenergy, substantially increases the global blue WF. Comparing feedstocks in the IEA 450 scenario shows that all feedstocks, except residues, generate WFs larger than the global WF over the period 1996–2005. Technology to convert residues into bioenergy is developing, e.g., thermochemical or biochemical conversions. There is large potential for residues, but new possibilities to convert residues into bioenergy need to be explored, combined with possible residue use elsewhere. © 2018, The Author(s).