WRF-Chem simulations in the Amazon region during wet and dry season transitions: evaluation of methane models and wetland inundation maps

International audienceThe Amazon region, being a large source ofmethane (CH4), contributes significantly to the global an-nual CH4budget. For the first time, a forward and inversemodelling framework on regional scale for the purpose ofassessing the CH4budget of the Amazon region is imple-mented. Here, we present forward simulations of CH4as partof the forward and inverse modelling framework based on amodified version of the Weather Research and Forecastingmodel with chemistry that allows for passive tracer transportof CH4, carbon monoxide, and carbon dioxide (WRF-GHG),in combination with two different process-based bottom-upmodels of CH4emissions from anaerobic microbial pro-duction in wetlands and additional datasets prescribing CH4emissions from other sources such as biomass burning, ter-mites, or other anthropogenic emissions. We compare WRF-GHG simulations on 10 km horizontal resolution to flask andcontinuous CH4observations obtained during two airbornemeasurement campaigns within the Balanc ̧o Atmosf ́ericoRegional de Carbono na Amazˆonia (BARCA) project inNovember 2008 and May 2009. In addition, three differentwetland inundation maps, prescribing the fraction of inun-dated area per grid cell, are evaluated. Our results indicatethat the wetland inundation maps based on remote-sensingdata represent the observations best except for the northernpart of the Amazon basin and the Manaus area. WRF-GHGwas able to represent the observed CH4mixing ratios bestat days with less convective activity. After adjusting wetlandemissions to match the averaged observed mixing ratios offlights with little convective activity, the monthly CH4bud-get for the Amazon basin obtained from four different sim-ulations ranges from 1.5 to 4.8 Tg for November 2008 andfrom 1.3 to 5.5 Tg for May 2009. This corresponds to an av-erage CH4flux of 9–31 mg m−2d−1for November 2008 and8–36 mg m−2d−1for May 200