Biomass production in plantations: Land constraints increase dependency on irrigation water

Abstract

Integrated assessment model scenarios project rising deployment of biomass‐using energy systems in climate change mitigation scenarios. But there is concern that bioenergy deployment will increase competition for land and water resources and obstruct objectives such as nature protection, the preservation of carbon‐rich ecosystems, and food security. To study the relative importance of water and land availability as biophysical constraints to bioenergy deployment at a global scale, we use a process‐detailed, spatially explicit biosphere model to simulate rain‐fed and irrigated biomass plantation supply along with the corresponding water consumption for different scenarios concerning availability of land and water resources. We find that global plantation supplies are mainly limited by land availability and only secondarily by freshwater availability. As a theoretical upper limit, if all suitable lands on Earth, besides land currently used in agriculture, were available for bioenergy plantations (“Food first” scenario), total plantation supply would be in the range 2,010–2,300 EJ/year depending on water availability and use. Excluding all currently protected areas reduces the supply by 60%. Excluding also areas where conversion to biomass plantations causes carbon emissions that might be considered unacceptably high will reduce the total plantation supply further. For example, excluding all areas where soil and vegetation carbon stocks exceed 150 tC/ha (“Carbon threshold savanna” scenario) reduces the supply to 170–290 EJ/year. With decreasing land availability, the amount of water available for irrigation becomes vitally important. In the least restrictive land availability scenario (“Food first”), up to 77% of global plantation biomass supply is obtained without additional irrigation. This share is reduced to 31% for the most restrictive “Carbon threshold savanna” scenario. The results highlight the critical—and geographically varying—importance of co‐managing land and water resources if substantial contributions of bioenergy are to be reached in mitigation portfolios.

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.…”

Growth and Physiological Responses of Yerba Mate Seedlings and Mini-Cuttings Under Drought Stress

“…In general, plantations productivity is closely related to water availability (Álvares-Dávila et al, 2017;Jans et al, 2018). When trees are under drought stress situations, a decrease in stomatal conductance and photosynthetic activity occurs (Chen, 2020), resulting in a lower total dry weight, decrease in leaf area, loss of leaves or even total defoliation (Monclus et al, 2006).…”

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

“…More recently, Yamagata et al (2018) suggested 1910 km 3 yr −1 of consumptive water demand for bioenergy crops to achieve NEs of 3.3 Gt C yr −1 , while Séférian et al (2018) estimate the water demand for producing 220-270 EJ in 2100 to be only 178 km 3 yr −1 , which is probably a result of strong restriction of irrigation and model limitations. Jans et al (2018) project a demand of 1,500-5000 km 3 yr −1 to generate 200-1000 EJ, while also securing environmental flow requirements (EFRs) with the prospect of maintaining freshwater ecosystems in a good state.…”