Satellite-based monitoring of methane emissions from China's rice hub

Rice cultivation is one of the dominant anthropogenic methane sources in China and globally. However, it is often challenging to accurately quantify national and regional rice methane emissions. Conventional bottom-up methods often rely on a small number of ground-based flux measurements to derive emission factors or to calibrate process-based models, despite of inherently high heterogeneity in rice methane emission intensities. Satellite observations provide an independent regional-scale constraint on the magnitude of rice methane emissions. We apply atmospheric methane observations from the Tropospheric Monitoring Instrument (TROPOMI) to a high-resolution (0.625° × 0.5°) inversion to estimate monthly methane emissions for 2021 from Heilongjiang province in Northeast China, which is the country’s largest rice province. Our optimal estimate of annual rice methane emissions is 0.89 (0.57 – 1.04) Tg a⁻¹, a factor of 2 or more higher than various bottom-up estimates. The results show that rice methane emissions in Heilongjiang peak during the tillering stage in June, consistent with intermittent flooding as the primary practice of water-regime management. This one-peak seasonality differs from the two-peak pattern in the prior estimate of the inversion (EDGAR v6.0) but agrees with flux measurements taken at a site in the region. Finally, our results are used to evaluate and improve process-based models of rice methane emissions.