Tropical floodplains have a significant impact on the regional water cycle and on land-atmosphere interaction but are not always considered in Land Surface Models (LSMs) or in Earth system models. This study evaluates the importance of representing tropical floodplains in an LSM to provide realistic river discharges, evapotranspiration fluxes and other variables crucial for land’s interaction with the ocean and atmosphere. Off-line simulations of the world’s largest tropical wetland, the Pantanal are conducted with ORCHIDEE, the LSM of IPSL’s regional and global Earth system model. We analyse the period 1961–2000, which includes both dry and wet decades. Atmospheric uncertainty is considered through the utilization of three forcing data sets, each one in two versions: the original dataset and a regionally bias adjusted version. The activation of the floodplain module leads to a systematic improvement of intra-annual variability and extremes of river discharge. Temporal evolution and spatial distribution of flooded area are coherent with satellite estimations, although the model, due to the coarse resolution of the topography, underestimates the extent of the area. Considering floodplains in ORCHIDEE enhance the evapotranspiration since it permits the water from the upstream region to evaporate in the plains. This have strong consequences on the water balance and on the spatial pattern of surface fluxes. The simulations allow us to perform a model-guided residual estimation of evapotranspiration through a water balance obtaining an annual evapotranspiration over Pantanal of 1220 mm while precipitation is estimated to be 1250 mm with an uncertainty of 180 mm.

热带洪泛区对区域水循环和陆地-大气相互作用具有重大影响，但在陆地表面模型（LSM）或地球系统模型中并不总是将其考虑在内。这项研究评估了在LSM中代表热带洪泛区的重要性，以提供现实的河流流量，蒸发蒸腾通量和其他对于陆地与海洋和大气相互作用至关重要的变量。使用IPSL区域和全球地球系统模型的LSM ORCHIDEE对全球最大的热带湿地Pantanal进行离线模拟。我们分析了1961–2000年，包括干旱和潮湿的十年。通过利用三个强迫数据集来考虑大气不确定性，每个强迫数据集采用两个版本：原始数据集和区域偏差调整版本。洪泛区模块的激活导致年内变化和河流排放极限的系统性改善。洪水区域的时间演变和空间分布与卫星估计一致，尽管由于地形的粗略分辨率，该模型低估了该区域的范围。考虑到ORCHIDEE中的洪泛区可提高蒸散量，因为它可使上游地区的水在平原上蒸发。这对水的平衡和地表通量的空间格局有很大的影响。该模拟使我们能够通过水平衡执行模型指导的蒸散的剩余估计，获得潘塔纳尔湿地的年蒸散量为1220 mm，而降水量估计为1250 mm，不确定性为180 mm。