The use of hydrological models to undertake climate change research raises the question of their robustness for use in a long-term projection when calibrated over a period in the recent past. The aim of this study was to assess the temporal transposability of the soil and water assessment tool (SWAT) model in the face of changes in climate and land use information. The model is set up on the Garonne River watershed in southwest France and two different tests were conducted: (1) two five-year periods were selected from the past 50 years: a dry and warm (DW) period and a wet and cold (WC) period. In this case, the model was calibrated for each period, and then each was cross-validated with the other; (2) the same process was undertaken using two sets of land use data from 1990 and 2006. The model was calibrated for the same time period (2000–2010), and each land use data set was cross-validated with the other. All four of the calibration/validation tests showed that the model was able to simulate the monthly stream effectively. Most of the 20 sites spread over the watershed have Nash-Sutcliffe criterion (NSe) and Nash-Sutcliff criterion calculated on the squared roots values of the discharge (NSeSqrt) above 0.75. The robustness of the SWAT model when confronted with changes to the climate or land use data was also very satisfactory: a variation of less than is induced for 14 sites and both metrics. Sites where simulations appeared more sensitive to those changes were either impacted by snowfall/melt processes during the winter season or by the low-flow support provided by hydraulic structure during the summer season in order to sustain irrigation. A change in land-use information caused even less instability: all 20 sites showed a variation in performances of less than for both metrics. It was concluded from this study that the SWAT model could be used over the Garonne River watershed in a climate change condition.