Freshwater requirements of large-scale bioenergy plantations for limiting global warming to 1.5 °C

Abstract

Limiting mean global warming to well below 2°C will probably require substantial negative emissions (NEs) within the 21st century. To achieve these, bioenergy plantations with subsequent carbon capture and storage (BECCS) may have to be implemented at a large scale. Irrigation of these plantations might be necessary to increase the yield, which is likely to put further pressure on already stressed freshwater systems. Conversely, the potential of bioenergy plantations (BPs) dedicated to achieving NEs through CO 2 assimilation may be limited in regions with low freshwater availability. This paper provides a first-order quantification of the biophysical potentials of BECCS as a negative emission technology contribution to reaching the 1.5°C warming target, as constrained by associated water availabilities and requirements. Using a global biosphere model, we analyze the availability of freshwater for irrigation of BPs designed to meet the projected NEs to fulfill the 1.5°C target, spatially explicitly on areas not reserved for ecosystem conservation or agriculture. We take account of the simultaneous water demands for agriculture, industries, and households and also account for environmental flow requirements (EFRs) needed to safeguard aquatic ecosystems. Furthermore, we assess to what extent different forms of improved water management on the suggested BPs and on cropland may help to reduce the freshwater abstractions. Results indicate that global water withdrawals for irrigation of BPs range between ∼400 and ∼3000 km 3 yr −1 , depending on the scenario and the conversion efficiency of the carbon capture and storage process. Consideration of EFRs reduces the NE potential significantly, but can partly be compensated for by improved on-field water management.

Irrigation of biomass plantations may globally increase water stress more than climate change

“…This approach enables us to highlight and quantify trade-offs regarding different levels of water protection, impacts of climate change versus mitigation through BECCS, and also the possible contribution of improved water management to help solve this dilemma. Unlike previous BECCS water demand studies 31 , 32 , we apply transient land use projections for both bioenergy and food crops 33 , which are consistent with future pathways of green-house gas emissions and socio-economic development.…”

“…The irrigation fraction is obtained from a sensitivity analysis as part of this study. Sustainable water management is a combination of withdrawal restrictions based on EFRs 35 , local water storage, and improved on-field irrigation efficiencies 32 , 34 .…”

Agriculture's Historic Twin-Challenge Toward Sustainable Water Use and Food Supply for All

“…Including application and conveyance losses, recent modeling studies confirm-in theory-that there are sizeable saving potentials in irrigated agriculture across regions worldwide. More than 40% of current irrigation water consumption might be accessible under ambitious irrigation transitions ( Table 1) to either reduce use or expand irrigated areas (Brauman et al, 2013;Fishman et al, 2015;Jägermeyr et al, 2016;Lopez et al, 2017;Stenzel et al, 2019;Huang et al, 2020). However, dynamic quantitative water accounting and local net effects of irrigation transitions in account of non-trivial water trade-off dynamics along the river network are difficult to assess at global scale (Munia et al, 2016).…”

Irrigation of biomass plantations may globally increase water stress more than climate change

“…To study the beneficial effects of more sustainable water use policies, we additionally explore scenarios with irrigated bioenergy plantations accompanied by sustainable water management (BECCS+SWM). This scenario assumes the preservation of environmental flow requirements (EFRs) and implements advanced on-field water management 31,32 on both agricultural and bioenergy sites. EFRs determine a percentage of pristine, undisturbed mean monthly river flow, here following a variable monthly flow (VMF) method 33 .…”

“…The irrigation fraction is obtained from a sensitivity analysis as part of this study. Sustainable water management is a combination of withdrawal restrictions based on EFRs33 , local water storage, and improved on-field irrigation efficiencies31,32 .…”