Quantification and evaluation of carbon emissions from irrigation water conveyance system in Southern Water Network Irrigation District

Sustainable irrigation areas are often required for the national low-carbon strategy. However, the current frameworks of agricultural carbon accounting cannot fully meet the requirements of emissions from infrastructure construction. This study aims to conduct a quantitative lifecycle assessment (LCA) of the irrigation water conveyance, namely the concrete block masonry channel (CBMC), the U-shaped precast concrete channel (UPCC), and the low-pressure polyethylene pipe (LPP), from the typical small-scale irrigation in the southern water network region. The emission-factor approach was also adopted to define the system boundary. Four consecutive stages were then selected, such as the material production, transportation, construction, and operation. Meanwhile, the activity data was derived from the engineering specifications, including the material quantities, transport distances, machinery usage, and energy consumption. The indicators of the carbon emission were acquired for the key materials (concrete, steel, timber, and polyethylene) and energy sources (diesel and grid electricity). The functional unit was assumed as the total carbon dioxide equivalent emissions over the projected service life, where the per unit irrigated area per year was set as the control. Results indicate that the production stage contributed 26.12% to 57.41% of the total emissions over the four lifecycle stages; The transportation was accounted for the smallest share (0.11%-1.57%); The construction contributed 0.46%-4.70%; The operation dominated with 38.37%-73.31%. The material production and operational energy use were identified as the dominant emission sources. Specifically, the concrete was the primary carbon source for the CBMC and UPCC, accounting for 53.08% and 17.85% of their total lifecycle emissions, respectively, whereas the polyethylene contributed 21.80% for the LPP. The electricity of the pumping was the most significant factor, thus representing 38.24%, 68.03%, and 73.28% of the total emissions for the CBMC, UPCC, and LPP during operation, respectively. Consequently, the LPP system demonstrated a markedly lower carbon footprint of 399 392.85 kg, compared with 1 000 875.28 kg for the CBMC and 537 746.62 kg for the UPCC, indicating the substantial potential for emission reduction in water and land savings. Furthermore, the UPCC was required only about one-fifth of the concrete volume in the CBMC, leading to a 66.97% reduction in emissions between the two channel types. The benefits of the precast technology were verified after evaluation. Sensitivity analysis revealed that the pump service life was the most influential parameter on the total carbon footprint, followed by the material transport distance. The annual carbon emissions were reduced to allocate from the production, transportation, and construction stages of the irrigation water delivery system, particularly with the increasing lifespan of the irrigation pumps. Correspondingly, there was a decrease in the annual carbon emission intensity per unit area. The material selection, structural optimization, and prefabricated elements were combined to reduce the embodied carbon. While the renewable energy of the pumping reduced the operational emissions greatlly. Some insights were derived from the conveyance components. The system boundary can be expanded to include the ancillary structures and end-of-life stages in future assessments. In conclusion, a practical LCA-based model was established to validate the decarbonization potential of the low-pressure pipe irrigation and prefabricated concrete channels. Thereby, the finding can also provide a strong reference for the low-carbon materials, engineering optimization, and clean energy in the irrigation areas in sustainable agriculture.