The 1960s Drought and the Subsequent Shift to a Wetter Climate in the Catskill Mountains Region of the New York City Watershed*

Abstract

The precipitation history over the last century in the Catskill Mountains region that supplies water to New York City is studied. A severe drought occurred in the early to mid-1960s followed by a wet period that continues. Interannual variability of precipitation in the region is related to patterns of atmospheric circulation variability in the midlatitude east Pacific-North America-west Atlantic sector with no link to the tropics. Associated SST variations in the Atlantic are consistent with being forced by the anomalous atmospheric flow rather than being causal. In winter and spring the 1960s drought was associated with a low pressure anomaly over the midlatitude North Atlantic Ocean and northerly subsiding flow over the greater Catskills region that would likely suppress precipitation. The cold SSTs offshore during the drought are consistent with atmospheric forcing of the ocean. The subsequent wet period was associated with high pressure anomalies over the Atlantic Ocean and ascending southerly flow over eastern North America favoring increased precipitation and a strengthening of the Northern Hemisphere storm track. Neither the drought nor the subsequent pluvial are simulated in sea surface temperature-forced atmosphere GCMs. The long-term wetting is also not simulated as a response to changes in radiative forcing by coupled models. It is concluded that past precipitation variability in the region, including the drought and pluvial, were most likely caused by internal atmospheric variability. Such events are unpredictable and a drought like the 1960s one could return while the long-term wetting trend need not continue-conclusions that have implications for management of New York City's water resources.

Hydroclimatic flood trends in the northeastern United States and linkages with large-scale atmospheric circulation patterns

“…However, our results and the recent work of others (Kingston et al 2007, Seager et al 2012 suggest that observed changes in flooding are at most complexly, and not exclusively, related to the NAO via its potential influence on storm tracks and antecedent soil moisture conditions. Floods are episodic phenomena, so we should also consider other recently documented changes in North Atlantic basin atmospheric conditions that may also affect conditions at the event scale.…”

“…In agreement, Polsky et al (2000) found a 10% increase in MAR monthly mean precipitation over the 20th century. Increases have been especially pronounced in the northeastern US (Groisman et al 2004, Madsen and Figdor 2007, Douglas and Fairbank 2011, Nguyen and DeGaetano 2012, Seager et al 2012. Regional temperatures have also increased over the 20th century (Groisman et al 2004).…”

“…Floods are episodic phenomena, so we should also consider other recently documented changes in North Atlantic basin atmospheric conditions that may also affect conditions at the event scale. Seager et al (2012) were unable to clearly identify a single mechanism for increased precipitation in the MAR after 1970, but they ruled out SST anomalies and instead concluded that the recent wet period is primarily a function of internal atmospheric dynamics. They document that the post-1970 increase in MAR precipitation is strongest in the spring and fall (which we note are the seasons that correspond with the primary and secondary streamflow maxima in the region, respectively), apparently related to atmospheric pressure anomalies that promote southeasterly (spring) and southwesterly (fall) ascending atmospheric flow that promotes enhanced precipitation.…”

“…In this study, we investigate the Mid-Atlantic region (MAR) of the US, which, like New England, has been characterized by increases in total annualand heavy precipitation (Groisman et al 2001, 2004, Madsen and Figdor 2007, Seager et al 2012. This extension substantially increases the number of climate sensitive gauges with long records that we can analyse in the northeastern United States-a region where any observed hydroclimatic changes in flood magnitudes and frequencies will have important consequences for human communities-and enables new analyses, interpretations, and comparisons with other recent national and regional investigations looking at climate-flood relationships via different metrics and using different criteria to select stream gauges for analyses (e.g.…”

Meteorological Aspects of the Eastern North American Pattern with Impacts on Long Island Sound Salinity

“…The cause of the 1960s drought is a subject of debate [12,13,54] and future research is needed to better understand it so that future droughts can be better anticipated. …”