The resilience of social-ecological systems and their capacity to adapt to change are valuable properties in face of global change. In those coupled systems overall dynamics are largely determined by feedbacks between the social and ecological components. Hence, to better understand their resilience the interactions of actors and institutions with the ecological system need to be explicitly taken into account. Using an agent-based modeling approach we investigate the behavior of human actors in a river basin in response to uncertain and varying resource availability to assess the effect of different institutional settings on the resilience of the coupled system. The model is a stylized representation of a river basin composed of human actors exploiting water-related ecosystem services. In the paper we analyze the impact of diversification of water use on the capacity of the system to deal with change in water availability and investigate under which conditions such a diversity might arise. The results show that diversification can mitigate upstream-downstream conflicts, improve system performance and enhance resilience, given different reactions of ecosystem services to resource variability. The outcomes are compared with an optimization of the trade-off in water use that serves as a benchmark for the agent-based model.