Assessment of Folsom lake response to historical and potential future climate scenarios: 1. Forecasting

In collaboration with operational forecast and management Agencies, an inte grated forecast-control system is designed and applied to a major reservoir in California to evaluate the potential benefits of climate information fo r flood control, hydroelectric energy production, and low flow augmentation . In addition to retrospective studies involving the historical period 1964 -1993, system simulations were performed for the future period 2001-2030, u nder a control and a 1% greenhouse-gas-increase scenario. This paper presen ts the forecast component formulation and validates ensemble 30-day reservo ir-inflow forecasts under a variety of situations. The control component fo rmulation and corresponding reservoir management results are presented in Y ao and Georgakakos, this issue. The forecast component is based on ensemble flow forecasting. Quantiles of the distribution of climate-model precipita tion simulations are used to select catchment-scale historical daily precip itation time series for the generation of an ensemble of daily reservoir-in flow by hydrologic models. Ensemble generation takes into consideration bot h atmospheric-forcing and hydrologic-model uncertainties. Principal conclus ions of this paper are that the integrated system provides reliable ensembl e inflow volume forecasts for the majority of the deciles of forecast frequ ency, and that the use of climate model simulations is beneficial mainly du ring high flow periods. It is also found that to maintain reliability for f uture climate periods, generation of ensemble inflow forecasts should use i nput time series that reflect potential sharp changes in precipitation amou nt. (C) 2001 Elsevier Science BN. All rights reserved.