Uncertainty in the evaluation of climate change impacts over two Mexican catchments

This study explores the uncertainties associated with general circulation model (GCM), emission scenarios and natural climate variability into estimates of climate change impacts over two Mexican catchments. The two selected catchments have contrasted climate patterns and hydrological regimes. Climate ensemble simulations from three GCMs under three SRES scenarios (B1, A1B, and A2) are considered to feed the physically-based semi-distributed SWAT hydrological model. The simulations cover the 30-year reference period (1971-2000) and two 20-year periods (2046-2065 and 2081-2100) in the future. For the set of hydrological indicators, the results show that the high flows are more prone to be influenced by the GCM uncertainty. A weak sensitivity of the hydrological indicators is observed to emission scenarios over the study catchments. We find that the uncertainty related to the natural climate variability should not be neglected in climate change impact studies, and appears, to some extent, to be as critical as the GCM and scenario uncertainties for high flows.