Transforming Global Climate Model Precipitation Output for Use in Urban Stormwater Applications

Abstract

Statistically downscaled global climate model (GCM) precipitation output is available for Philadelphia, but the temporal resolution is too low for direct use in model-based urban stormwater applications. Additionally, GCM output for Philadelphia does not accurately represent local storm intensities and durations. To address these limitations, this study presents an innovative approach employed by the Philadelphia Water Department (PWD) to transform GCM output into actionable science that can directly inform planning, design, and engineering applications, including hydrologic and hydraulic (H&H) modeling and intensity-duration-frequency curve development. This approach uses GCM output for current (1995–2015) and future (2080–2100) conditions under a certain greenhouse gas emission trajectory to develop delta change factors based on season and storm size. These factors are then used to create a plausible future hourly time series. A stochastic generator was also developed that utilizes the adjusted future time series to explore potential variability in projected precipitation patterns. The approach presented in this study is practical and transferable, addressing the need for actionable climate change information in the field of water resource management.