Background
With respect to possible recent changes in flood risk throughout the United States, the author notes "there is broad evidence ... for increased magnitudes of low and moderate flows both regionally and nationally," but that "trends in high flows have been much less evident [our italics]," as he reports that "at a national scale, only a small proportion of the gages measuring dominantly natural streamflow (i.e., minimal regulation, diversion, or land use impacts) show upward trends in the annual maximum average daily discharge."

What was done
Working with data obtained from 28 streamflow gages of the Hydro-Climate Data Network scattered throughout New England that were not influenced by regulation and had continuous data that spanned at least the last half of the 20th century and continued through 2006, Collins looked for evidence of any trends or step changes that might have occurred over this period.

What was learned
Averaging 75 years in length, 25 of the 28 streamflow records showed "upward trends via the nonparametric Mann-Kendall test, 40% of which are statistically significant (p < 0.1)," while "an average standardized departure series for 23 of the study gages indicates that increasing flood magnitudes in New England occurred as a step change [our italics] around 1970."

What it means
Interestingly, this somewhat rare case of flood risk increase in the United States arrived in the form of a step increase near the end of a 30-year cooling of the globe, about five years prior to the start of the late 20th-century warming that climate alarmists blame for almost everything imaginable that has a negative connotation attached to it. It would be very difficult, however, for them to blame it for Collins' findings.