Increasingly, engineers must make estimates of discharge associated with a particular risk (or set of risks) to design a hydraulic structure or stormwater management facility considering potential climate change. As part of a national cooperative highway research program (NCHRP) study “Applying Climate Change Information to Hydrologic and Hydraulic Design of Transportation Infrastructure,” the authors examined issues and proposed strategies for adapting downscaled global climate model (GCM) precipitation outputs as inputs to rainfall/runoff models used in hydrologic design. This paper describes the recommendations for estimating projected precipitation based on the downscaled outputs of GCMs. It provides actionable guidance for estimating projected daily precipitation data for use in rainfall/runoff modeling for many applications. It describes a 10-step procedure that includes selection of a portfolio of downscaled GCM outputs using alternative greenhouse gas scenarios. The procedure describes a method for using GCM-based information in conjunction with historical precipitation for estimating projected precipitation. The procedure generates estimates of mean values and confidence limits for each scenario. Finally, the paper illustrates derivation of sub-daily precipitation estimates and discusses the limitations of—and alternatives to—these methodologies.