Since 2008 we have been monitoring a watershed in the alps to assess the impact of the spatial heterogeneity of meteorological variables over a complex terrain and identify the mechanisms generating streamflow. The study area is located in the Swiss Alps along the southernmost ridge that borders Italy. The watershed is heavily monitored with wireless meteorological stations, measuring precipitation, solar radiation, air temperature and humidity, skin temperature, wind speed and direction, soil temperature and humidity, and soil matrix potential. During the 2011 field campaign, the discharge of two sub-basins has been monitored in order to compare the results with a semi-distributed model. Moreover, water from different rivers of the basin has been sampled automatically, along with water samples from precipitation, in order to proceed to a two-component hydrograph separation with stable isotopes analysis. We discuss the relative importance of snowmelt, precipitation and local geomorphology, based on the results of different models in combination with the data collected in the past years.