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According to climate and hydrological conditions, large tropical areas would potentially be covered by forests. Remote sensing and field surveys, however, show how these regions may differ from their potential original states because land use, such as logging, agriculture and pastures. Related processes also contribute to the replacement of forests by secondary and degraded vegetation, and to the establishment of savannas. Fires are such a process normally associated to the current land-use practices in the tropics. Because savannas are adapted to fires and benefit from their occurrence, forest-to-savanna transitions are potentially very stable near deforestation areas. Here we present a method to account for deforestation and fires on the distribution of tropical and seasonal forests and savannas in the Brazilian Amazonia, and underline some strategies for implementing it in long-term vegetation models. We analyzed soil-hydrology and fires occurrence data together with the results from the potential vegetation model CPTEC-PVM2, and explored two factors used to determine the potential distribution of major biomes in that model. One is a soil-moisture seasonality index (D) which is lower (higher) for places where the soil presents longer (shorter) dry periods. Other is an above-ground wetness index (H) which is lower (higher) for longer (shorter) periods of dry atmospheric conditions. The analysis indicated the most common values for both indexes in areas potentially covered by tropical forests in the Brazilian Amazonia that had low, medium and high fire activity in the years 1998-2005 according to active-fire detections with the Tropical Rainfall Measuring Mission – Visible and Infrared Scanner (TRMM-VIRS). For each fire-activity class, we determined the distribution of values for both indexes and found the values below which deforestation/fire degradation were relatively more frequent. We now plan to use these relations when accounting for deforestation/fires in projections of the spatial distribution of the major biomes in the region. For that, we selected and discuss the following strategy that we consider appropriated. First, we assume that land-use dynamics and policy currently observed in the Brazilian Amazon will remain in the future. Second, we consider that deforestation/fires will affect forests only in grid cells of tropical and seasonal forests that are located adjacent (<150km) to savannas, because the access to the forests is facilitated by the savannas where fires are also a natural feature. In summary, if a place projected to be covered by tropical or seasonal forest presents both indexes H and D below certain thresholds, and the area is adjacent to a savanna, then tropical forest will be adjusted to seasonal forest. In case of a seasonal forest it will be adjusted to savanna. Although our method may represent an underestimation of fire effects by not considering direct transitions from tropical forests to savannas, it allows for quantifying changes in vegetation cover including human factors, and based on simple general relations derived using data from the region.