Hydrological and vegetation response to climate change in a forested mountainous catchment

Vegetal cover and the water cycle are closely linked. The climate controls the distribution and productivity of terrestrial vegetation, and the vegetal cover type is a key determinant for evapotranspiration and global runoff. In this study, a dynamic vegetation model (LPJ) has been coupled with a 3D hydrogeological model (MODFLOW) to estimate, for the first time, the impact of climate change on a small forested temperate watershed (Strengbach, Vosges, France). The model, calibrated with monthly hydrological and climate data, is able to globally reproduce the observed vegetal cover distribution and the water cycle over the 1987–2009 period. The discrepancies between calculated and observed intra-annual discharge variations highlight the importance of processes such as snow formation, snowmelt, and catchment recharge after drought periods, as well as the impact of evapotranspiration. Long-term simulations extending up to the year 2100 have been performed with climatic output from the Meteo-France climate model ARPEGE/Climate (IPCC, 2007 scenario A1B). With a predicted increase in temperature of 2.6 °C and a rise in atmospheric CO2 concentration of 80%, the mean annual precipitation decreases by 4.5% in the Strengbach watershed over the course of the century. The models cascade predicts a limited decrease of evapotranspiration (by 2.5%), an impact on discharge (11% decrease) at the watershed outlet over the 21st century, and a significant change in vegetation distribution starting in approximately 2085. The response of land plants to climate change in the future seems to only slightly affect the water resources in the Strengbach catchment. This study also highlights existing shortcomings and limitations of simulations for measuring the impacts of climate change.