April 2012 article (Early View): “Increased Frequency of Low-Magnitude Floods in New England,” by William H. Armstrong, Mathias J. Collins, and Noah P. Snyder.
Although catastrophic floods are usually responsible for channel avulsions, stream barrier breaches (e.g., dams), and transporting large bed-load particles, floods occurring every one or two years are more active agents in shaping the prevailing channel dimensions because of their frequency and ability to erode and transport bank and bed material. Frequent, low-magnitude floods are also important for riparian and aquatic habitat.
The authors selected gauges from the USGS Hydro-Climatic Data Network (HCDN), a compilation of river gauges that are minimally affected by human use and are the best available representation of natural streamflow throughout the U.S. They found widespread upward trends in peak over threshold per water year (POT/WY) – a direct measure of increasing flood frequency – on New England rivers. Twenty-two of 23 study gauges selected for climate sensitivity show increasing trends in POT/WY through the analysis of long-term records. They found evidence for a step increase in POT/WY around 1970 on more than half of the rivers, and seven rivers show evidence for a step increase in flood discharge, supporting recent studies noting change points in time series of various hydrologic variables around that time.
[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own.]
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