Assessing water system vulnerabilities under changing climate conditions using different representations of a hydrological system

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Changes in climate are altering the historical characteristics of the streamflow regime and affecting the performance of water systems. Here, the role of representing natural streamflow conditions in quantification of water system vulnerability under changing climate is evaluated in the Oldman River Basin, Canada. Four hydrological models are developed using point- and grid-based climate data and considering lumped and semi-distributed representations of the watershed. These hydrological models are then coupled with a reservoir water allocation model. Using an ensemble of climate model projections fed into these integrated models, changes in the water system’s behaviour are evaluated. Although intensified and earlier peak flows and more critical water deficits are projected, the estimated risks of failure strongly depend on the considered hydrological model configuration. The divergence among models’ projections for water deficit can be as high as 300%. Therefore, usage of all configurations is recommended to revise the reservoir operational policies.