The Effect Of Storm Direction On Flood Frequency Analysis

Storm direction modulates a hydrograph's magnitude and duration, thus having a potentially large effect on local flood risk. However, how changes in the preferential storm direction affect the probability distribution of peak flows remains unknown. We address this question with a novel Monte Carlo approach where stochastically transposed storms drive hydrologic simulations over medium and mesoscale watersheds in the Midwestern United States. Systematic rotations of these watersheds are used to emulate changes in the preferential storm direction. We found that the peak flow distribution impacts are scale-dependent, with larger changes observed in the mesoscale watershed than in the medium-scale watershed. We attribute this to the high diversity of storm patterns and the storms' scale relative to watershed size. This study highlights the potential of the proposed stochastic framework to address fundamental questions about hydrologic extremes when our ability to observe these events in nature is hindered by technical constraints and short time records.Plain Language Summary Estimating the likelihood of extreme events such as floods is becoming more challenging because climate change affects storm patterns worldwide. This study focuses on understanding how storm direction affects the probability distribution of peak flows, which is essential for floodplain mapping and engineering design of resilient infrastructure under future climate. Our results suggest that storm direction has minor implications for these probability distributions in medium-sized watersheds or smaller (order of 4,000 km(2)) but can significantly affect larger watersheds, particularly for the largest flood events. Our findings point to avenues for future interdisciplinary analyses of the complex, dynamic role of rainfall structure in flooding.Key PointsThe importance of storm direction in peak flow distribution is mainly driven by the relative difference of storm and watershed sizeExpected changes in predominant storm trajectories can significantly modify peak flow distributionsRegionalization of peak flow distributions should account for the effects of the relative orientation of storms and watersheds