Regional climate influences manure temperature and methane emissions - A pan-Canadian modelling assessment

This study explores the variation of liquidmanure temperature (T-m) and CH4 emissions associated with contrasting regional climates, inter-annual weather variation, and manure storage emptying. As a case-study, six regions across Canada were used, spanning 11 degrees 32' latitude and 58 degrees 30' longitude. Annual average air temperatures ranged from 3.9 degrees C (prairie climate) to 10.5 degrees C (maritime climate), with an overall average of 6.6 degrees C. A model predicted Tm over 30 years, using daily weather (1971-2000), and over one "normal" year (30-year average weather). Modelled T-m was then used in Manure-DNDC to model daily CH4 emissions. Twomanure storage emptying scenarios were simulated: (i) early spring and autumn, or (ii) late spring and autumn. Regional differences were evident as average Tm ranged from 8.9 degrees C to 14.6 degrees C across the six locations. Early removal of storedmanure led to warmer Tm in all regions, and the most warming occurred in colder regions. Regional climate had a large effect on CH4 emissions (e.g. 1.8x greater in the pacificmaritime and great lakes regions than the prairie region). Inter-annual weather variability led to substantial variation in inter-annual CH4 emissions, with coefficient of variation being as high as 20%. The large inter-annual range suggests that field measurements of CH4 emissions need to compare the weather during measurements to historical normals. Early manure storage emptying reduced CH4 emissions (vs late removal) in some regions but had little effect or the opposite effect in other regions. Overall, the results from this modelling study suggest: i) Tm differs substantially from air temperature at all locations, ii) accurate estimates of manure storage CH4 emissions require region-specific calculations using T-m (e.g. in emission inventories), iii) field measurements of CH4 emissions need to consider weather conditions relative to climate normal, and iv) emission mitigation practices will require region-specific measurements to determine impacts. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.