Abrupt change in runoff on the north slope of the Catskill Mountains, NY, USA: Above average discharge in the last two decades

• Increased seasonal flow variability in this watershed will impact downstream basins.
• Above average flow during the winter but shorter peak flow periods.
• Average or below average flow during the summer low-flow periods.
• Shorter comparison periods enable identification of possible analog regimes.
• Increased variability limits predictability and increases exposure to risk.

Study regionSchoharie Creek, Catskills Mountains, New York, USA.Study focusTotal annual flow in Schoharie Creek, Catskills Mountains, was above the long-term average for most of the last two decades. We hypothesize that the end of the 20th century and early 21st century mark a change in the streamflow in the Schoharie watershed. To test this, we evaluated annual flow, center-volume (CV) and winter–spring center-volume (WSCV) dates, and average daily flow within four comparison periods purposefully selected to represent: average conditions, below average, above average and recent conditions Recurrence intervals of the 2-yr, 5-yr, and 10-yr daily maximum flow calculated for the comparison periods suggested that these event magnitudes were larger during the last decade.New hydrological insights for the regionThe increase in high-frequency event magnitude was most pronounced at the 5-yr daily maximum flow in the lower Schoharie. During the last decade the 5-yr event magnitude exceeded the record-long 10-yr daily maximum flow magnitude. Changes to peak daily flow implies more flow in the lower Schoharie more frequently. Seasonal differences drive above average winter runoff, shortened peak runoff in spring and in several cases below average summer and late summer flow. This flow pattern is not just a matter of more water all the time, but more water during the high-flow period and less water during the low-flow period, intensifying annual extremes.