Summary:
The increasing demands for palatable drinking water as a result of increasing utilization has
made an exact assessment of availability from the major watersheds that supply the New York
City metropolitan area necessary. The historic precipitation regimes of three New York State
Hudson Valley watershed tributaries that provide the major portion of New York City 's water
supply were examined by mean of network of rain gages that monitor daily precipitation within
each of the Croton, Esopus, and Schoharie catchment basins. It was found that the wettest is
the Esopus with a mean annual total of 50.31 inches and a range of extremes from 31. 63 to
66.89 inches. The Croton watershed shows a mean annual total of 46. 05 inches with annual
extremes ranging from 33.10 to 63.76 inches. The driest is the Schoharie with a mean annual
total of 44.15 inches with annual extremes ranging from 30.19 to 58.40 inches. Annual and
monthly normals plus daily extremes were analyzed for three individual rain gages located
within each watershed. Standard deviations from the mean annual and monthly precipitation
totals reveal the great variability within each of the tributary basins. Such variability
poses long-term environmental risks in rapidly urbanizing townships. Digital Fourier Spectral
Analysis shows significant periodicity peaks for annual totals at 48.8, 25-26.4 , 17.1-18.4,
and 4.5 years. Filtered annual totals show that the drought of the 1960s was the major
hydrologic event in the 20th century.
