Stochastic Method for Examining Vulnerability of Hydropower Generation and Reservoir Operations to Climate Change: Case Study of the Dworshak Reservoir in Idaho

Changes in air temperature and precipitation that are due to climate change can affect operational objectives and hydropower production of reservoirs. This study uses a stochastic conceptual snowmelt-runoff model to generate inflow ensembles for a wide range of potential temperature and precipitation scenarios as a means of testing which types of climate changes could adversely affect hydropower production. The method is applied to a case study of the Dworshak Reservoir on the North Fork of the Clearwater River in central Idaho. Reservoir operations in response to the climate-change ensemble scenarios were simulated using a decision support system operations model according to current operating criteria and guidelines. The magnitude and timing of hydropower generation resulting from each temperature- and precipitation-change scenario were examined, assuming no change from historical reservoir operations. Results showed that lower precipitation and higher temperature created less runoff and therefore less hydropower generation. However, increased precipitation and decreased temperature scenarios showed limited increases in hydropower production due to turbine capacity and other operational constraints. Firm hydropower production from Dworshak steadily decreased with increasing mean annual temperature and steadily increased with increasing mean annual precipitation. Timing of spring hydropower production shifted to earlier spring and winter with increasing temperature. Because these simulations did not adapt reservoir operations from historical procedures, they are not intended to be realistic predictions of changes in hydropower generation in the future. Rather, the results demonstrate how the approach can provide guidance about which types of hydrograph changes, such as shifts in inflow timing, might warrant changes in reservoir operations. (C) 2014 American Society of Civil Engineers.