Modeling landfill CH4 emissions: CALMIM international field validation, using CALMIM to simulate management strategies, current and future climate scenarios

Authors: Spokas, Kurt; BOGNER, J. - University Of Illinois; CORCORAN, M. - General Dynamics

Submitted to: Elementa: Science of the Anthropocene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2021
Publication Date: 11/9/2021
Citation: Spokas, K.A., Bogner, J., Corcoran, M. 2021. Modeling landfill CH4 emissions: CALMIM international field validation, using CALMIM to simulate management strategies, current and future climate scenarios. Elementa: Science of the Anthropocene. 9(1). Article 00050. https://doi.org/10.1525/elementa.2020.00050.
DOI: https://doi.org/10.1525/elementa.2020.00050

Interpretive Summary: The impact of future climates on soil systems is of concern to several different ecosystems. One of these is the prediction of landfill methane emissions, since these emissions are reduced by the action of soil bacteria to oxidize the methane gas as it diffuses through the soil. The purpose of this manuscript was to further validate an existing mechanistic model for landfill emissions (CALMIM) using data from 26 different international landfill sites. Additionally, this is the first report on the impact of landfill emissions based on climate change model predictions. This research concluded that future landfill surface emissions are more dependent on precipitation forecasts than corresponding temperature increases in future climate scenarios. These results are significant to assist scientists, engineers, farmers, as well as supplying guidance for modeling the soil ecosystem response to future climate alterations.

Technical Abstract: The current Intergovernmental Panel on Climate Change [IPCC] greenhouse gas (GHG) inventory methodology for landfill CH4 emissions excludes critical process drivers now known to control surface emissions. These include 1) site operational factors (e.g., the area, thickness, and physical properties of site-specific cover soils; the extent of engineered gas recovery) and 2) seasonal climatic effects on cover soil moisture and temperature which drive gaseous transport, methanotrophic oxidation, and temporally-variable “net” emission rates from each cover soil over an annual cycle. Improved site-specific emissions estimates, as opposed to existing IPCC-reported national annual estimates, require consideration of both site-specific climate (e.g., 30-year climatic averages; annual weather; future climate projections) as well as site-specific cover properties and other site management strategies. Herein, we address a detailed international field validation and application of a process-based model [CALMIM] originally developed and field-validated for California landfills. Via embedded soil microclimate models with default 30-yr climate data [0.5o X 0.5o] or site-specific annual weather data (daily min/max temperature, daily precipitation), the soil moisture and temperature effects on diffusive gaseous transport and microbial oxidation can be estimated for each site-specific cover soil at any global location. From model results for 2.5-cm depth increments and 10-min time intervals, standard CALMIM output includes graphics illustrating surface emissions “with” and “without” oxidation for each cover soil during a typical annual cycle, as well as calculated average monthly emissions with standard deviations. Our modeled results bracketed 86% of 81 individual surface methane measurement comparisons across 26 international sites. Notably, the model over-predicted only 4 comparisons and under-predicted 7 comparisons. In addition to improving site-specific landfill CH4 inventories, this freely available tool can a) provide insight into alternative cover designs to minimize emissions at a particular site; b) systematically examine the spatial and temporal variability of emissions for differing global settings (e.g., latitudinal gradients; extreme climates; future climate scenarios); c) assist scheduling of field campaigns to capture seasonal variability, and d) provide a comparative annual framework for diverse bottom-up and top-down field measurements with variable uncertainties. Importantly, CALMIM does not require intensive site-specific model calibrations. It is also the first tool to permit quantitative estimation of future CH4 emissions via direct input of standardized climate projections for any global location (e.g., IPCC CMIP5 scenarios).