The analysis of climatic and anthropogenic effects on mesoscale river basins has become one of the main concerns for hydrologists, environmentalists, and planners during the last decade. Many attempts at dealing with this issue have been proposed in the literature. In most studies, however, the main components of the system have been isolated in order to reduce the complexity of the system and its intrinsic uncertainty. In this paper, an attempt to couple two realms of the water system at a mesoscale catchment, namely, the hydrological behaviour of a catchment and the state of the land cover at a given point in time, is presented. Here, instead of using a standard hydrological model, various nonlinear models relating several runoff characteristics with physiographic, land cover, and meteorological factors were linked with a stochastic land use/cover change model. Then, using this integrated model, the magnitude of the effects of the hydrological consequences of land use/cover and climatic changes was assessed in a probabilistic way by a sequential Monte Carlo simulation provided four different scenarios which take into account likely developments of macroclimatic and socioeconomic conditions relevant for a given study area. The proposed methodology was tested in a river basin of approximately 120 km2 located to the south of Stuttgart, Germany.