Seasonal Variations of CH4 Emissions in the Yangtze River Delta Region of China Are Driven by Agricultural Activities

Abstract

Developed regions of the world represent a major atmospheric methane (CH 4 ) source, but these regional emissions remain poorly constrained. The Yangtze River Delta (YRD) region of China is densely populated (about 16% of China's total population) and consists of large anthropogenic and natural CH 4 sources. Here, atmospheric CH 4 concentrations measured at a 70-m tall tower in the YRD are combined with a scale factor Bayesian inverse (SFBI) modeling approach to constrain seasonal variations in CH 4 emissions. Results indicate that in 2018 agricultural soils (AGS, rice production) were the main driver of seasonal variability in atmospheric CH 4 concentration. There was an underestimation of emissions from AGS in the a priori inventories (EDGAR-Emissions Database for Global Atmospheric Research v432 or v50), especially during the growing seasons. Posteriori CH 4 emissions from AGS accounted for 39% (4.58 Tg, EDGAR v432) to 47% (5.21 Tg, EDGAR v50) of the total CH 4 emissions. The posteriori natural emissions (including wetlands and water bodies) were 1.21 Tg and 1.06 Tg, accounting for 10.1% (EDGAR v432) and 9.5% (EDGAR v50) of total emissions in the YRD in 2018. Results show that the dominant factor for seasonal variations in atmospheric concentration in the YRD was AGS, followed by natural sources. In summer, AGS contributed 42% (EDGAR v432) to 64% (EDGAR v50) of the CH 4 concentration enhancement while natural sources only contributed about 10% (EDGAR v50) to 15% (EDGAR v432). In addition, the newer version of the EDGAR product (EDGAR v50) provided more reasonable seasonal distribution of CH 4 emissions from rice cultivation than the old version (EDGAR v432).

Agricultural Methane Emissions in China: Inventories, Driving Forces and Mitigation Strategies

“…Currently, the most widely adopted methods for estimating agricultural methane emissions are bottom-up or top-down methods, which are applied at various temporal and spatial scales. ,, Some studies on methane emission inventories for livestock and rice cultivation ,− have focused on improving methane emissions at a fine scale and correcting localization parameters, emission mechanisms, and behavioral habits. ,, Moreover, the demand for food production and meat supply is closely related to both socioeconomic development and agricultural methane emissions . Currently, sector-specific and region-specific socioeconomic drivers of agricultural methane emissions in China have not been precisely identified, which hinders the ability of policymakers to formulate targeted policies.…”

Evolution of Atmospheric Carbon Dioxide and Methane Mole Fractions in the Yangtze River Delta, China

“…From 2013 to 2016, the CO 2 mole fractions in summer mornings were lower than those of other seasons, because the wind speed in this period was lower than that in other seasons, resulting in uneven atmospheric mixing. However, the CH 4 mole fractions in summer were higher than those in the other seasons during the same period, because high temperatures and heavy precipitation were conducive to CH 4 production in wetlands [41,42], especially in 2016, when the precipitation in YRD in summer was 20% to 1 time more than that in previous years. Additionally, the marine seeps from the East China Sea may contribute to the higher CH 4 mole fractions due to the high sea surface temperature during 2013-2016 [9,43].…”

“…However, in summer, autumn, and winter, the amplitudes were quite different from 2010-2012 and 2013-2020 (about 10 ppb). Although the paddy rice field area decreased in recent decades with the continuous expansion of urbanization area in the YRD region, the rice yields increased, leading to the increase of anthropogenic CH 4 emissions in summer and autumn [42,44]. In addition, energy consumption generally increased in winter, especially of natural gas, leading to higher CH 4 mole fractions [45].…”

A benchmark dataset of diurnal- and seasonal-scale radiation, heat and CO<sub>2</sub> fluxes in a typical East Asian monsoon region

“…The YRD (26-34 • N, 114-122 • E), located in a typical East Asian monsoon region, is one of the most developed areas in China (Yang et al, 2020a;Zhang et al, 2021;Chen et al, 2022). The region occupies only 2.2 % of the area of China, but it is home to about 16 % of China's total population (Huang et al, 2021) and contributed approximately 18.5 % of China's gross domestic product in 2014 (Hu et al, 2018). Land cover types in the YRD are diverse and are dom-inated by cropland, built-up areas, and mountainous areas (mostly forests and grasslands) across the northern, central, and southern parts of the region, respectively (Fig.…”