Evaluating the impact of climate change on water system vulnerabilities using multiple hydrological models

Warming climate is altering streamflow characteristics and posing pressure on water systems. Here, the impacts of climate change on a headwater system in Alberta, Canada, is evaluated, with the primary goal of understanding the role of hydrological system representation. For this purpose, a conceptual hydrological model, i.e., HBV-MTL, is coupled with two snowmelt estimation modules, i.e., Degree-Day and CemaNeige. The models are calibrated using point- and grid-based climatic data and considering lumped and semi-distributed representation of the basin and are linked to a water allocation model to simulate reservoir dynamics and downstream water deliveries. The bias-corrected outputs of 19 climate models during 2021-2099 are then used to estimate the future water system conditions. Results show that during the historical period, all models provide acceptable performance, with minor distinctions; however, their simulations highly divergence in the future period. The models unanimously project significant water deficit in meeting agricultural water demands and flood risk in the future. However, the quantified vulnerabilities depend on the considered hydrological models, among the utilized snow routine module highly influences estimated natural and regulated flow values. It is suggested to consider these projections and revise the Oldman reservoir water allocation plans to mitigate climate change's adverse impacts on this water system.