Half of the world's population depends on fresh water that originates from mountains. In the present-day, it is apparent that climate change will affect these mountain water resources. Therefore, some crucial questions are often raised: Will mountain rivers continue to provide the same amount of fresh water as they have in the past? Have there been any changes in the hydrological regime of mountainous watersheds? Is there a chance that the flow magnitude and timing will change? In order to answer these questions, this research attempts to understand the hydrological regime of the Rhone River watershed, located in the southwestern part of Switzerland. The objective is to simulate streamflow and assess its sensitivity due to changes in land-use and climate. A hydrological model was developed to simulate the streamflow and forecast future scenarios. Complexity due to anthropogenic influences such as hydropower based water transfer and natural variability (e.g. snow melt, glacier melt, orographic precipitation) was incorporated into this model. The study suggests an early summer melt and reduction of summer flow. The results obtained can be of added value to impact assessment studies for better understanding of water management and biodiversity in watersheds with similar hydro-physiographic constraints.