Abstract
Snowfall in the six basins of the Catskill/Delaware Watershed in south‐central New York State historically contributes roughly 20–30% of the water resources derived from the watershed for use in the New York City water supply. The watershed regularly experiences snowfall from three distinctive weather patterns: coastal mid‐latitude cyclones, overrunning systems, and lake‐effect or Great Lakes enhanced storms. Using synoptic weather classification techniques, these distinct regional atmospheric patterns impacting the watershed are isolated and analysed in conjunction with daily snowfall observations from 1960 to 2009 to allow the influence of each synoptic weather pattern on snowfall to be evaluated independently.Results indicate that snowfall‐producing events occur on average approximately 63 days/year, or once every 4 days during the October–May season, leading to an average of 213 cm/year of snowfall within the watershed. Snowfall from Great Lakes enhanced storms and overrunning systems contribute nearly equally to seasonal totals, representing 38 and 39%, respectively. Coastal mid‐latitude cyclones, while producing the highest amount of snowfall per event on average, contribute only 16% to the watershed average total snowfall. Predicted climate change is expected to impact snowfall differently depending on the specific atmospheric pattern producing the snow. As such, quantifying the contribution of snowfall to the watershed by synoptic pattern can inform future water management and reservoir operation practices for the New York City Water Supply Management System.
Highlights
Snowfall is an important component of the New York City Water Supply System (NYCWSS) that supplies water for the consumption and sanitation needs of roughly 9 million second largest reservoir used for NYC water needs
NYCWSS derives approximately 90% of its water from the eral, the watershed is subject to three general categories of six basins of the Catskill/Delaware Watershed (CDW), atmospheric conditions leading to snowfall: coastal midlocated in the Catskill Mountains of south-central New York latitude cyclones, overrunning systems, and lake-effect or
The region most closely corresponding to the CDW in the 1 data set includes observation stations that are outside the boundaries of the watershed; comparisons can still be drawn to this study
Summary
Snowfall is an important component of the New York City Water Supply System (NYCWSS) that supplies water for the consumption and sanitation needs of roughly 9 million second largest reservoir used for NYC water needs. The synoptic weather types created by a temporal synoptic index (TSI; Kalkstein and Corrigan, 1986) are qualitatively grouped into one of three general categories of coastal mid-latitude cyclones, overrunning systems, and Great Lakes enhanced pattern; the resulting snowfall associated with each is examined This approach allows for the influence of each synoptic category on snowfall to be determined independently, and to quantify their respective relative contribution of total snowfall. Percent of total snowfall, frequency of snowfall events, and the average magnitude of snowfall per event are examined for each of the three synoptic categories across the watershed to understand the relative contribution to snowfall from each category These variables are investigated as a 1960–2009 average, inter-annually, and FIGURE 2 Composite sea level pressure fields (hPa) for representative examples of the three snowfall-inducing synoptic categories (a) type OR-1 (overrunning), (b) type CO-3 (coastal), and (c) type LE-4 (Great Lakes enhanced). To determine if changes to the snowfall associated with these synoptic categories occurred, long-term trends are examined using ordinary least-squares linear regression
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