Enhanced contribution of wetland methane variability during recent El Nino

Wetlands are thought to be the dominant contributor to interannual variability in atmospheric methane (CH4) with a strong influence from the El Niño-Southern Oscillation (ENSO). However, whether the increase in emissions during El Nino droughts versus La Nina pluvial is from wetlands versus fire is unclear. Here we use a terrestrial ecosystem model LPJ-wsl that included permafrost and wetland dynamics, and compare how three climate datasets with different temporal resolution (daily: MERRA2, ERA-Interim; monthly: CRU), to simulate the spatio-temporal dynamics of wetland CH4 emissions from 1980-2016 to compare it against the MEI ENSO index and in-site surface observations. We find that strong El Niño event in 2015-2016 caused a record-high growth rate of wetland CH4 emissions compared to previous decades, which was mainly due to the combined effects of droughts and widespread warming over tropics on soil respiration. Our study will bring new insights into the role of wetlands in driving the variability of atmospheric CH4.