Recent and future changes in extreme rainfall in the Catskills region of New York

Abstract

Recent flooding events in the Catskills such as Tropical Storm Irene have raised concerns regarding changes in the frequency of heavy rainfall. The extreme precipitation records of four long-term observing sites are analyzed based on two measures of heavy rainfall. The number of events that produce ≥50.8 mm of precipitation per year show little evidence of an increasing trend. Rather, the climatology of Catskills stations is marked by considerable year-to-year and decade-to-decade variability. Because of this variability, a different measure of extreme precipitation, the 100-year storm, attained its highest value in the early 1960s. This was an artifact of the reliance of the analysis procedure on a relatively short record that coincided with high precipitation. Current engineering design for infrastructure affected by extreme rainfall is based on this metric. After 1960, the 100-year storm declined, until rising again after 1990. This rise is consistent with a regional trend toward higher precipitation extremes. Climate-model projections show this trend continuing at a rate of 2-3% per decade through 2069. The serendipitously high 100-year-storm value computed in 1960 may provide some buffer to the expected effects of this change in extreme rainfall in the Catskills.