This paper presents a regional model, based on Positive Mathematical Programming, which aims to evaluate the consequences of Fischler reform on the agricultural sector of the Lombardy irrigated lowland (Northern Italy). The model main focus is to quantify the agricultural land use changes due to the farmers reaction to the CAP reform main issues, such as single payment, and to simulate possible scenarios for the future. The model takes into account also the Water Frame Directive principles, in order to combine the assessment of both CAP issues and the potential irrigation water supplies reduction, which could deeply affect the area. The model input are obtained by means of the integration between FADN and SIARL (Agricultural Information System of Lombardy Region) information, in order to fit the territorial dimension. The simulation results of 11 different scenarios are discussed.