Examining Shifts in Timing of Peak Flows in Northeast US Rivers and Implications for Changes in Future Flood Risk (Invited Presentation)

While multiple studies have found the center of volume of cumulative discharge has begun to occur earlier in the year on rivers in the Northeastern U.S., there does not appear to be much analysis of the change in timing of annual peak flows. While the timing of the center of volume and the peak would be presumed to be related, the peak flow would be most directly related to the timing and magnitude of flood events. Thus, understanding changes in the timing of peak flows may be useful to predict changes in future flood risk.

In this analysis, we examine changes in the timing of annual maximum and peak-over-threshold time series of flows for 20 rivers in New York, Massachusetts, and Pennsylvania (watersheds which have snow, but which are not snow-dominated). Only timing of winter and spring flows are included; we do not include peaks that occur in summer and fall in the analysis. Changes in magnitude for these winter and spring peaks are assessed in addition to changes in timing. Initial analyses suggests that peak flows have been occurring earlier in recent decades (not unexpected given the known shift in the center-of-volume of flow) but that the magnitude of flow of these winter and spring peaks has not changed significantly. Each peak flow is also characterized by precipitation, snow pack, and estimated soil wetness at the time of the event to provide insight into how root, causative factors of floods may be changing in time and how these relate to the lack of observed change in magnitude of the peaks.