Studying the processes responsible for the distribution of water resources in a river basin over space and time is of great importance for spatial planning. In this study a multi-agent simulation approach is applied for exploring the influence of alternative reservoir operation strategies on water use distribution in the semi-arid Jaguaribe basin in case of decreasing rainfall. Water use distribution is analyzed both for one specific subbasin – our study area – and for the river basin level. Agents in this study are farmers that adapt to local variations in water availability. In this way both natural and human influences on water availability are taken into account. This study shows that a decrease in rainfall and runoff in the Jaguaribe basin leads to a transition of water use from the dry season to the wet season. The dry season water use decreases because of reduced water availability in the dry season. This mainly is the result of reduced rainfall and runoff in the wet season and the consequent increased water use for irrigation in the wet season. A decrease in rainfall and runoff also leads to a relative transition of water use from downstream to upstream at the basin scale. Strategic reservoir operation enables local water managers to offset the effect of decreasing rainfall and runoff with regards to water use at the subbasin level, at the cost of further decreasing water availability at the basin level.