A Seasonal Shift in the Frequency of Extreme Hydrological Events in Southern New York State

Abstract

The recent sequence of extreme hydrological events across the eastern United States (e.g.

Tree-Ring Investigation of Holocene Flood-Deposited Wood From the Oneida Lake Watershed, New York State

“…Modern Fish Creek runoff is strongly influenced by the seasonal distribution of precipitation, with maximum river discharge in spring from melted snow and prominent rainstorms (Matonse and Frei 2013). The increase in the number of extreme floods across the U.S. Northeast in the last decade is attributed to the highest frequency of extreme warm-season precipitation events in the last 100 years (Collins 2009;Matonse and Frei 2013), particularly associated with high-precipitation events promoted by tropical cyclones and organized extratropical systems (Smith et al 2011;Dai 2013). The dated episodes of wood deposition may result from a similar increase in frequency of such extreme summer precipitation events in the area .…”

Hydrological and temperature variations between 1900 and 2016 in the Catskill Mountains, New York, USA

“…Annual precipitation patterns follow a unimodal seasonal distribution, with the highest levels of precipitation occurring in the months of August–October, associated with both mid‐latitude storms as well as the influence of tropical moisture (Towey et al ., ). Streamflow, on the other hand, follows a bimodal seasonal distribution, with the largest annual values usually occurring in March–April, but sometimes during August–October (Matonse and Frei, ). Large streamflow events are caused by a combination of antecedent conditions and precipitation (Lumia et al ., ; Ivancic and Shaw, ; Fang and Pomeroy, ).…”

“…Large streamflow events are caused by a combination of antecedent conditions and precipitation (Lumia et al ., ; Ivancic and Shaw, ; Fang and Pomeroy, ). Antecedent conditions are associated with snowmelt and other cold season processes during spring, whereas in the fall they are associated primarily with soil saturation (Matonse and Frei, ; Frei and Kelly‐Voicu, ).…”

“…In the Catskills Mountains of south‐central New York State, mean air temperature increased between 1952 and 2005 by 0.6°C, accompanied by a 136 mm increase in mean precipitation and a 16 mm increase in potential evapotranspiration (Burns et al ., ). Changes in Catskill streamflow have also been observed, including an earlier spring timing of peak flow and an increase in the frequency and magnitude of extreme streamflow mainly during the warm season (Matonse and Frei, ). These changes, which are more apparent in the higher elevation regions including the Rondout and Neversink watersheds located on the southeastern side of the region, are likely related to the earlier melting of the snowpack, decrease in the amount of precipitation falling as snow, and larger increases in magnitude and frequency of extreme precipitation events during the warm season (Zion et al ., ; Matonse et al ., ; Frei et al ., ).…”

“…In the Catskills, the wet period that followed the drought of the 1960s and continues into the 21st century appears to be unprecedented over the past 500 years (Pederson et al ., ). The station record indicates that the years 2003–2012 experienced the greatest frequency of warm season extreme hydrological events on record, and extreme 4‐day precipitation events during the warm season have increased in frequency by about 150% during the 2000s (Matonse and Frei, ; Frei and Kelly‐Voicu, ). The flooding events of August and September, 2011, which included Tropical Storms Irene and Lee, were the largest events on record (Frei and Kelly‐Voicu, ).…”