Abstract
Abstract. Many scenarios of future climate evolution and its anthropogenic drivers include considerable amounts of bioenergy as a fuel source, as a negative emission technology, and for providing electricity. The associated freshwater abstractions 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 abstractions for bioenergy production and puts these estimates into the context of scenarios of other water-use sectors. We scanned the available literature and (out of 430 initial hits) found 16 publications (some of which include several bioenergy-water-use scenarios) with reported values on global irrigation water abstractions for biomass plantations, suggesting water withdrawals in the range of 128.4 to 9000 km3 yr−1, which would come on top of (or compete with) 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 calculate an inverse water-use efficiency (iwue), which facilitates comparison of the required freshwater amounts per produced biomass harvest. We conclude that due to the potentially high water demands and the tradeoffs 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 abstractions, full disclosure of parameters and assumptions is crucial. A minimum set should include the complete water balances of bioenergy production systems (including partitioning of blue and green water), bioenergy crop species and associated water-use efficiencies, rainfed and irrigated bioenergy plantation locations (including total area and meteorological conditions), and total biomass harvest amounts. In the future, a model intercomparison project with standardized parameters and scenarios would be helpful.
Highlights
Previous assessments of global green and blue water requirements of a potential widespread bioenergy industry show a large variation in the estimates, while there is still insufficient analysis of the underlying sources of variation and assumptions that need to be standardized.Projections of future energy demand and its partitioning increasingly assume replacement of carbon-intense fossil en-Published by Copernicus Publications on behalf of the European Geosciences Union.F
We scanned the Web of Science and the SCOPUS database on 5 February 2020 with a query covering all global bioenergy with carbon capture and storage (BECCS) and bioenergy studies that mention use, consumption, withdrawal, or demand of water in their abstract, keywords, or title and excluded studies which focused on algae or electrofuels: ("BECCS" OR "bioenergy production" OR "bioenergy cultivation" OR "biomass production" OR "biomass plantation*") AND (( "water" AND ("use" OR "demand" OR "consumption" OR "withdrawal")) OR "irrigation") AND ("global") NOT ("algae" OR "algal" OR "electrofuels")
If deriving global estimates of Bioenergy plantations (BPs) freshwater withdrawal or consumption is an aim of a study, more straightforward and computationally inexpensive estimations might suffice
Summary
In order to limit mean global warming to 2 ◦C or even 1.5 ◦C (UNFCCC, 2015), technologies providing additional negative emissions (NEs) are potentially needed to compensate for residual and past emissions (Rockström et al, 2017; Minx et al, 2018; Rogelj et al, 2018). One such NE technology (NET) is bioenergy with carbon capture and storage (BECCS). Due to the large amount of potentially needed NEs in the second half of the century (e.g. 3.3 GtC yr−1 reported by Smith et al, 2016 and 2–5 GtC yr−1 reported by Rogelj et al, 2015), the feedstock is projected to be grown on large managed plantations and include substantial irrigation, demanding tradeoffs between negative emissions and area requirements as well as water consumption to be solved sustainably
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