Satellite-Based Monitoring of Methane Emissions from China’s Rice Hub

Rice cultivation is one of the major anthropogenic methane
sources
in China and globally. However, accurately quantifying regional rice
methane emissions is often challenging due to highly heterogeneous
emission fluxes and limited measurement data. This study attempts
to address this issue by quantifying regional methane emissions from
rice cultivation with a high-resolution inversion of satellite methane
observations from the Tropospheric Monitoring Instrument (TROPOMI).
We apply the method to the largest rice-producing province (Heilongjiang)
in China for 2021. Our satellite-based estimation finds a rice methane
emission of 0.85 (0.69–1.03) Tg a–1 from
the province or an average emission factor of 22.0 (17.8–26.6)
g m–2 a–1 when normalized by rice
paddy areas. The satellite-based analysis reveals a 2 to 4 times lower
bias in widely used global and national inventories, which lack up-to-date
regional information. The inversion reduces the uncertainty of regional
rice emissions by 73% relative to bottom-up estimates based on field
flux measurements. The satellite inversion also shows that the highest
rice methane emissions occur in June during the tillering stage of
rice, decreasing toward ripening, indicating that the predominant
water management practice in the region involves drainage and intermittent
flooding after initial flooding. Process-based modeling further suggests
that this practice can lead to a reduction of methane emissions by
more than 50% compared to continuous flooding of rice paddies and
natural wetlands.