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Potential changes in climate are expected to lead to future changes in the characteristics of precipitation events, including extreme rainfall intensity in most regions. In order for government agencies and design engineers to incorporate these trends and future changes into assessment and design processes, tools for planning and design should be capable of considering nonstationary climate conditions. In this work, potential changes are investigated in intensity-duration-frequency (IDF) curves, which are often used for assessment of extreme rainfall events, using historic data and future climate projections. An approach is proposed for calculating IDF curves that incorporates projected changes in rainfall intensity at a range of locations in the United States. The results elucidate strong regional patterns in projected changes in rainfall intensity, which are influenced by the rainfall characteristics of the region. Therefore, impacts of climate change on extreme hydrologic events will be highly regional and thus such assessments should be performed for specific project locations.

Estimates of a channel's annual sediment transport capacity typically incorporate annualized flowduration curves. Average daily flow data, commonly used to develop flow-duration curves, may not adequately describe sediment-transporting flows in arid and semiarid ephemeral streams. In this study, we examined impacts of varied temporal resolution flow data on annual sediment load estimation. We derived flow-duration curves for eight sites in the Southwestern United States based on both 15-min and daily-averaged flow data. We then estimated sediment loads for both flow-duration curves using the Sediment Impact Analysis Method, implemented in HEC-RAS. When average daily flow is used to generate flow-duration curves, sediment load estimation is lower by up to an order of magnitude. This trend is generally unaffected by uncertainty associated with sediment particle size or hydraulic roughness. The ratio of sediment loads estimated by 15-min versus dailyaveraged flow-duration curves is strongly correlated with channel slope, being greater on steep-slope channels. Sediment loads estimated by the two types of flow-duration curves are closely correlated, suggesting possible relationships for improving predictions when high-temporal resolution data are unavailable. Results also suggest that the largest flow contributes significantly to total sediment load, and thus will greatly impact ephemeral stream geomorphology in arid and semiarid regions.