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Abstract:
Many scenarios of future climate evolution and its anthropogenic drivers include considerable amounts of bioenergy as fuel source, negative emission technology, or for final energy production. The associated freshwater requirements for irrigation of dedicated biomass plantations might be substantial and therefore potentially increase water limitation and stress in affected regions; however, assumptions and quantities of water use provided in the literature vary strongly. This paper reviews existing global assessments of freshwater requirements for such bioenergy production and puts these estimates into the context of scenarios for other water use sectors. We scanned the available literature and (out of 430 initial hits) found 16 publications (partly including several scenarios) with reported values on global water demand for irrigation of biomass plantations, suggesting a range of 125–11,350 km3 yr−1 water use (consumption), compared to about 1,100–11,600 km3 yr−1 for other (agricultural, industrial, and domestic) water withdrawals. To provide an understanding of the origins of this large range, we present the diverse underlying assumptions, discuss major study differences, and make the freshwater amounts involved comparable by estimating the original biomass harvests from reported final energy or negative emissions. We conclude that due to the potentially high water demands and the trade-offs that might go along with them, bioenergy should be an integral part of global assessments of freshwater demand and use. For interpreting and comparing reported estimates of possible future bioenergy water demands, full disclosure of parameters and assumptions is crucial. A minimum set should include annual blue water consumption and withdrawal, bioenergy crop species, rainfed as well as irrigated bioenergy plantation locations (including total area), and total bioenergy harvest amounts.
