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Climate impacts have been causing changes in weather patterns, increasing extreme weather events, and changing the frequency and timing of rain events, causing them to happen earlier in the season leading to rain-on-snow events. These events generate more runoff compared to rainfall or snowfall alone, making them a critical concern for stormwater management. While rain-on-snow events have been studied in mountainous regions, research on their impacts in urban areas with high imperviousness in the United States remains limited and stormwater systems are designed without considering ROS impacts. Previous literature revealed that Low Impact Development designs and detention ponds worked best in cold climates to mitigate excess runoff.Ìý

In this study, historical climate data from the National Weather Service was used to analyze the frequency and extremity of rain-on-snow events in Cleveland Ohio, with their hydrologic impacts simulated through the Storm Water Management Model (SWMM). The study aims to improve the identification of rain-on-snow events and assess key characteristics and drivers. We found that varying definitions of rain-on-snow events can influence the number and type of events identified. Of particular interest were those events that have a significant hydrologic impact in urban areas, causing more runoff. Those events are better identified with a combined criterion and are found to generate substantially greater hydrologic response.Ìý

Results indicate that the precipitation component of rain-on-snow events plays a crucial role in driving snowpack melting and increased runoff generation. Compared to elevated temperatures alone, rainfall was the dominant factor in accelerating snowmelt and producing higher peak flows. Notably ROS events resulted in 18% higher peak flows compared to an all rainfall condition. These findings highlight the significance of precipitation as a primary driver in rain-on-snow events and the need to adapt stormwater infrastructure to account for such events in urban environments. Future studies should further investigate mitigation strategies that reduce runoff impacts in urban settings.