Abstract
This article presents the results and validation of a comprehensive, multi-decadal, hindcast simulation performed using the New York Harbor Observing and Prediction System´s (NYHOPS) three-dimensional hydrodynamic model. Meteorological forcing was based on three-hourly gridded data from the North American Regional Reanalysis of the US National Centers for Environmental Prediction. Distributed hydrologic forcing was based on daily United States Geologic Survey records. Offshore boundary conditions for NYHOPS at the Mid-Atlantic Bight shelf break included hourly subtidal water levels from a larger-scale model ran for the same period, tides, and temperature and salinity profiles based on the Simple Ocean Data Assimilation datasets. The NYHOPS model’s application to hindcast total water level and 3D water temperature and salinity conditions in its region over three decades was validated against observations from multiple agencies. Average indices of agreement were: 0.93 for storm surge (9 cm RMSE, 90% of errors less than 15 cm), 0.99 for water temperature (1.1 °C RMSE, 99% of errors less than 3 °C), and 0.86 for salinity (1.8 psu RMSE, 96% of errors less than 3.5 psu). The model’s skill in simulating bottom water temperature, validated against historic data from the Long Island Sound bottom trawl survey, did not drift over the years, a significant and encouraging finding for multi-decadal model applications used to identify climatic trends, such as the warming presented here. However, the validation reveals residual biases in some areas such as small tributaries that receive urban discharges from the NYC drainage network. With regard to the validation of storm surge at coastal stations, both the considerable strengths and remaining limitations of the use of North American Regional Reanalysis (NARR) to force such a model application are discussed.
Highlights
Every year since 1976 has had an average global temperature warmer than the long-term average
The completed multi-decadal high-resolution three-dimensional hindcast simulation for Long Island Sound (LIS) and New York/New Jersey Harbor (NYNJH) was based on a nested modeling concept utilizing two hydrodynamic domains (Figure 1): The Stevens North Atlantic Predictions model (SNAP) [9,10,11] and the New York Harbor Observing and Prediction System model (NYHOPS, www.stevens.edu/New York Harbor Observing and Prediction Systems (NYHOPS)) [9,11,12,13,14,15,16,17,18]
The model’s grand-mean temperature and salinity bias against all Long Island Sound Study observations in the Sound was found to be 0.18 ◦C warmer for water temperature, and 1.31 psu saltier for salinity; these biases were assumed constant in time and space and were removed from all raw NYHOPS model gridded time series results
Summary
Every year since 1976 has had an average global temperature warmer than the long-term average. Over the 1979–2013 period, global temperature warmed at an average of 0.26 ◦C per decade over land and 0.10 ◦C per decade over the global ocean [1]. The Northeast US shelf waters have experienced higher warming rates than the global ocean, deduced by the Sea Surface Temperature (SST) satellite record. The sole long-term observation record for water temperatures within the Long Island Sound (LIS) estuary, a US Estuary of National Significance, at a location near Millstone CT [4] has measured a much more rapid increase in LIS water temperatures than the global average: an alarming 0.44 ◦C per decade between 1979 and 2013, over four times higher than the global average rate. Over coastal Connecticut counties, on LIS’s northern coast, surface air temperatures for the same time period increased by 0.33 ◦C per decade; that rate was double if only the 1992–2012 period was considered, but has decreased somewhat since, to 0.28 ◦C per decade (1979–2015; [1])
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