Sensitivity analysis of distributed environmental simulation models: understanding the model behaviour in hydrological studies at the catchment scale

The development of new hydrological simulation tools allows for the modelling of large hydrological catchments, with the aim of comprehensive management of the water resources, control of diffuse pollution processes, such as the fate of agricultural fertilizants and finally, with purposes of economical optimization of the crop yields as a function of the expected climate, the watershed characteristics and the socio-economical conditions of the region where the catchment is located. This paper describes the sensitivity analysis of a hydrological distributed model applied in one large European watershed by using a two-step procedure. Firstly, it allows for the consideration of a huge input parameter data set by using an implementation of the Morris screening procedure, eschewing the huge computational requirements arising from the necessary repetitive simulations. In the second step it provides quantitative estimations of sensitivity in terms of variance decomposition procedures based upon the FAST method for both the hydrological and the water quality determinants.