RAIN ON SNOW FLOODING EVENTS AND CLIMATE CHANGE IN THE UPPER SUSQUEHANNA RIVER BASIN AT OWEGO, NY

A rain on snow (ROS) precipitation event in 1996 was followed by widespread flooding throughout New York State, with the town of Owego, NY recording a peak flow of 81,400 cfs at USGS stream gage 01513831 located along the Susquehanna River in the Upper Susquehanna Basin resulting in an observed crest of 32.97 ft on January 20. An estimated 7.8 million dollars in county wide damages to both private property and public infrastructure occurred. Therefore, it is important not only to understand the spatial and temporal relationships of ROS events, but also what effect climate trends may have on their frequency and severity.

The 1996 event was modeled for the town of Owego, NY using precipitation data obtained from NOAA and stream flow records archived by the USGS, then compared to other gage sites along the Susquehanna River as well as peak flows occurring in other years during the month of January. The storm was also modeled using a DEM processed in QGIS from 1mm LiDAR in HEC-RAS to provide a base for constructing a storm specific flood hazard map. Regional RCP-8.5/4.5 precipitation and temperature trajectories for the month of January were used to assess future risk.

Preliminary results yield a relationship between annual peak flows occurring during the month of January and unseasonable air temperatures, however, they do not assume an increased level of ROS flood hazard. While average maximum temperature and total precipitation are predicted to increase by as much as 1.6 degrees Fahrenheit and 0.3 inches respectively by the years 2035-2039 for the month of January in Tioga County, subsequent peak flows at Owego, NY in January of 1999, 2010, and 2012, were caused by precipitation accumulations of at least 2 inches during periods of high air temperatures near or above 50 degrees Fahrenheit, yet snow depths were not adequate to increase run-off to a hazardous level.

Current climate predictions indicate ROS derived flood events may continue to be anomalies or decrease in frequency in the Upper Susquehanna Basin. Further data analysis should be performed for sites within other New York State drainage basins as well as sites with flood events comparable to Owego, NY that have more complete stream gage and precipitation records. It may also be pertinent to address the potential for any increased flood hazard purely due to storm runoff in the winter months.