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

This study explores the variation of liquid manure 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°32' latitude and 58°30' longitude. Annual average air temperatures ranged from 3.9 °C (prairie climate) to 10.5 °C (maritime climate), with an overall average of 6.6 °C. A model predicted T_m 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. Two manure storage emptying scenarios were simulated: (i) early spring and autumn, or (ii) late spring and autumn. Regional differences were evident as average T_m ranged from 8.9 °C to 14.6 °C across the six locations. Early removal of stored manure led to warmer T_m in all regions, and the most warming occurred in colder regions. Regional climate had a large effect on CH₄ emissions (e.g. 1.8× greater in the pacific maritime 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) T_m 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.