Herman, J., Zeff, H., Lamontagne, J., Reed, P.M., and Characklis, G., “Synthetic Drought Scenario Generation to Support Bottom-Up Water Supply Vulnerability Assessments.”, Journal of Water Resources Planning and Management, v142, no. 11, 2016.
http://ascelibrary.org/doi/10.1061/%28ASCE%29WR.1943-5452.0000701
Robustness analyses of water supply systems have moved toward exploratory simulation to discover scenarios in which existing or planned policies may fail to meet stakeholder objectives. Such assessments depend on the development of plausible future scenarios, which, in the case of drought management, requires sampling or generating a broad ensemble of reservoir inflows which extends beyond the historical record. This work adapts synthetic streamflow generation to allow adjustable frequency of low-flow periods. The approach facilitates robustness assessments of urban water supply systems for scenarios in which impactful historical droughts become more frequent. Specifically, the contributed streamflow generation procedure allows the user to specify parameters n, p such that events with observed weekly non-exceedance frequency p appear in the synthetic scenario with approximate frequency np (i.e., the pth percentile flow occurs n times more frequently). Additionally, the generator preserves the historical autocorrelation of streamflow and its seasonality, as well as approximate multi-site correlation. Using model simulations from recent work in multi-objective urban drought portfolio planning in North Carolina, a region whose water supply faces both climate and population pressures, we illustrate the decision-relevant consequences caused by raising the frequency of low flows associated with the 2007-2008 drought. This method explores system performance under increased drought frequency based on stakeholder experience prior to reconciling these findings with climate model projections, and thus can be used to support bottom-up robustness methods in water systems planning.