Modelling the impact of agri-environmental scenarios on runoff in a cultivated catchment (Normandy, France)

Over the last 30 years, European agricultural policy has influenced agricultural practices. These have led to an increase in numerous environmental issues such as the erosion and runoff risk, which have reached an alarming level in loamy soils of Upper Normandy. To control runoff and erosion at catchment scale, public authorities need tools in order to obtain a better knowledge of present or future pressure on the environment. With such information, it will be easier to act locally on a problem by avoiding negative impacts elsewhere in the area. us models have been developed to assess the impacts of land-use modifications. This paper presents a brief description of the remote sensing version of STREAM, called STREAM-TED, which then is used to estimate and map runoff according to various scenarios of rain event and land-use distribution in a cultivated catchment. Three kinds of scenarios of land-use modifications have been considered: partial or complete reduction of grassland in favour of cash crops, modifications of agricultural practices on arable lands, and insertion of water management on the catchment. Results of 11 management scenarios tested showed the negative effect of a partial or complete ploughing of permanent grassland. Changes on arable land scenarios showed that these modifications reduced runoff in various ways according to rainfall events. The scenario with the most significant impact consists of simulating the introduction of 100% more environmentally friendly production methods on arable lands. With this scenario, runoff is practically eliminated for winter rainfall events and is decreased twofold for summer rainfall events. In addition, it is the only scenario which leads to a significant runoff volume reduction even with a “catastrophic” rainfall event.