Hydrological responses of a watershed to historical land use evolution and future land use scenarios under climate change conditions

Abstract

Abstract. Watershed runoff is closely related to land use, but this influence is difficult to quantify. This study focused on the Chaudière River watershed (Québec, Canada) and had two objectives: (i) to quantify the influence of historical agricultural land use evolution on watershed runoff; and (ii) to assess the effect of future land use evolution scenarios under climate change conditions (CC). To achieve this, we used the integrated modeling system GIBSI. Past land use evolution was constructed using satellite images that were integrated into GIBSI. The general trend was an increase of agricultural land in the 1980s, a slight decrease in the beginning of the 1990s and a steady state over the last ten years. Simulations based on thirty years of daily meteorological series showed strong correlations between land use evolution and water discharge at the watershed outlet, especially for summer and fall seasons. For the prospective approach, we first assessed the effect of CC and then defined two opposite land use evolution scenarios for the horizon 2025 based on two different trends: agriculture intensification or sustainable development. Simulation results showed that CC would induce an increase of water discharge during winter and a decrease the rest of the year, while land use scenarios would have a more drastic effect, agriculture intensification counterbalancing the effect of CC during summer and fall. Due to the large uncertainty linked to CC simulations, it is difficult to conclude that one land use scenario provides a better adaptation to CC than another, but this study shows that land use is a key factor that has to be taken into account when predicting potential future hydrological responses of a watershed.