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Seasonal inundation determines the structure and function of tropical floodplain ecosystems, and therefore information on the spatial and temporal variability of inundation is fundamental to understand and manage these ecosystems. This study uses the 37-GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (SMMR: Nimbus-7 satellite) to reveal inundation patterns in the Pantanal, a vast savanna floodplain located largely in Brazil. We calculated inundation area separately for 10 subregions using mixing models that account for the major landscape units with distinctive microwave emission characteristics. Maximum inundation occurred as early as February in the northern subregions and as late as June in the south, reflecting the delayed drainage of the region. As much as 131,000 km(2) was inundated annually during the 9 years of SMMR observations (1979-87). Monthly estimates of the total area inundated in the region varied from 11,000-110,000 km(2), averaging 53,000 km(2). We reconstructed regional inundation pat terns over the past 95 years from the correlation between the Paraguay River stage and total inundation area during the SMMR period. Both the maximum and minimum inundation area showed large interannual variability

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