Linked Rainfall and Runoff Intensity-Duration-Frequency in the Face of Climate Change and Uncertainty
Dr. Yonas Demissie | Washington State University
Storm water and flood management infrastructures are commonly designed to handle specific design storms derived from at-site historical rainfall intensity-duration-frequency (IDF) curves based on the assumptions that rainfall patterns and distributions are (1) spatially similar within the drainage area and (2) will remain unchanged throughout the design lifetimes of the infrastructures. The presence, however, of significant spatial variability and potential future change in rainfall patterns due to climate change might violate these assumptions and lead to inaccurate IDF curves, which in turn can have serious impacts on the design, operation, and maintenance of existing and new military installation infrastructure. This project will address this need by providing the Department of Defense (DoD) with an innovative framework that integrates methodologies for regional, adaptive, and probabilistic estimation of rainfall and runoff IDF curves, taking into consideration the spatial variation of precipitation in drainage areas and impacts of future climate change and uncertainty. The framework will be applied for 13 DoD installations across different geographic and climate regions to assess the potential risk of severe storms and resulting floods to existing installations, with the overall goal of improving understanding of future risk and enhancing DoD’s effort toward cost-effective improvement of military installation readiness in the face of anticipated impacts of climate change and uncertainties.
Depending on topographic and climatic variations within a region, rainfall patterns and the atmospheric processes driving them can vary significantly, both spatially and temporally, making it essential to incorporate these variations fully when constructing IDF curves for the region. Mountains, for example, often have a strong influence on the flow of air and solar radiation, leading to considerable spatial variations in rainfall. Climate change, on the other hand, might introduce new trends, variations, and extremes that cannot be captured by historic data alone. In addition, historical/future climate variations can contain uncertainties, limiting the applicability of IDF curves.
To represent these natural processes and climate change effects properly in IDF curves, this project will integrate computational algorithms that have proven successful in various research projects and applications. An innovative framework will be developed to (1) use the modified L-moment algorithm to regionalize IDF curves and improve the representation of spatial variation and coverage of rainfall for various durations and climate scenarios; (2) use the Bayesian algorithm to incorporate into IDF curves the uncertainties related to the fitted probability distribution model, historical data, and climate projection; (3) use the recursive Bayesian algorithm to update IDF curves and incorporate recent observations and future projections of extreme rainfall events from state-of-the-art, high-resolution dynamic downscaling; (4) use the Rational and Technical Release 55 (TR-55) runoff estimation methods and hydrologic model as well as snowmelt estimation to link rainfall and runoff IDF curves and directly assess flood risk and incorporate human effects on the rainfall-runoff relationship; (5) use open-source software to develop an interactive web-based Geographic Information System (GIS) tool and a geo-database and facilitate construction and updating of the rainfall and runoff IDF curves for any military installation and region of interest to DoD.
This research will result in novel approaches for developing next-generation IDF curves that are expected to improve understanding and benefit DoD’s effort to assess the risks posed by climate change and uncertainty to military installations and to develop effective adaptation strategies. Applications for 13 installations and a sample facility illustration will be demonstrated to the facility stakeholders via an interactive web-based GIS tool, web-based seminars, and a user guide. All methodologies, data sets, and analysis tools developed will be provided to DoD for use in decision-making and planning exercises. (Anticipated Project Completion - 2019)