The authors explore the uncertainty implied in the estimation of changes in flood frequency\ndue to climate change at the basins of the Cedar River and Skunk River in Iowa, United States.\nThe study focuses on the influence of climate change on the 100-year flood, used broadly as a\nreference flow for civil engineering design. Downscaled rainfall projections between 1960ââ?¬â??2099 were\nused as forcing into a hydrological model for producing discharge projections at locations intersecting\nvulnerable transportation infrastructure. The annual maxima of the discharge projections were used\nto conduct flood frequency analyses over the periods 1960ââ?¬â??2009 and 1960ââ?¬â??2099. The analysis of\nthe period 1960ââ?¬â??2009 is a good predictor of the observed flood values for return periods between 2\nand 200 years in the studied basins. The findings show that projected flood values could increase\nsignificantly in both basins. Between 2009 and 2099, 100-year flood could increase between 47%\nand 52% in Cedar River, and between 25% and 34% in South Skunk River. The study supports a\nrecommendation for assessing vulnerability of infrastructure to climate change, and implementation\nof better resiliency and hydraulic design practices. It is recommended that engineers update existing\ndesign standards to account for climate change by using the upper-limit confidence interval of the\nflood frequency analyses that are currently in place.
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