Hurricane Harvey was an unprecedented event that resulted in immense damage to life and property. As a result, it is important to determine how this event, as well as past and future events like it, will impact engineering design equations that are based upon historical data, such as flood frequency analysis equations. This study seeks to contribute to this discussion by evaluating the extent to which Harvey influenced estimations of instantaneous peak discharges in rural ungauged basins in southeast Texas. Results indicate that Harvey significantly increased the computations of design floods using Log-Pearson Type III analysis (e.g., 3-55% for 2-year flood and 3-80% for the 100-year flood). This subsequently impacted the estimation of instantaneous peak discharges through regional flood frequency analysis by up to 28%. These results highlight the influence that recent and future hurricanes can have on engineering design equations that are used for managing floodplains, assessing flood risk, and designing infrastructure such as levees, bridges, and culverts. K E Y W O R D Sflood frequency, floods, global warming, hurricane Harvey, peak discharge, regional flood frequency analysis, regional regression, streamflow

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Hurricane Harvey produced unprecedented flooding that altered flood frequency statistics near Houston, Texas. While Harvey could have made landfall elsewhere along the Gulf coast, traditional flood frequency methodologies only consider the risk of Harvey in the region that it hit. This may be a shortcoming of flood frequency methodologies as the intensity of Harvey was greater due to climate change; therefore, Harvey may be more indicative of future hurricanes than other historical observations. To that end, this study investigates what effect Harvey would have had on flood frequency statistics if it had made landfall elsewhere. To do so, a Monte Carlo simulation was used to shift Harvey's rainfall within alternative landfall locations. This rainfall was then applied to synthetic unit hydrographs to estimate peak flows that were applied in Log Pearson III and Regional Flood Frequency Analyses. Log Pearson III analyses with simulated Harvey streamflows produced median 100‐year peak flows that were 17%–66% higher than analyses that only used historical records. A regional flood frequency analysis in the central coastal geomorphologic region of Texas showed that predictive equations, based upon basin area and shape factor, had an average increase of 30.2% in the 100‐year peak discharge.

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