Evaluating Regional Methane Emission in New Zealand Using Inverse Modelling

Abstract:

Agriculture accounts for nearly half of New Zealand’s greenhouse gas emissions, primarily from enteric fermentation. Knowing this and that the farming sector must make progress in reducing emissions at the farm scale before joining New Zealand's emissions trading scheme by 2025, it is vitally important to be able to monitor emissions rather than relying solely on bottom-up estimates. In this paper we present early results of a study into regional methane emissions of New Zealand using in-situ measurements of methane at NIWA’s world class observations sites, the NAME dispersion model and a Bayesian regional inversion scheme. The early inversion results for 2017-2019 show that quantifying sub-national, monthly methane emissions is possible with strong error reduction and high degrees of freedom, particularly for strongly emitting, observation adjacent regions. We will also show the extent to which these results are dependent on the baseline, inter-site biases and the dispersion and meterological modelling used in order to provide a robust and policy relevant quantification of sub-national, monthly methane emissions.