An Open-Access, Multi-Decadal, Three-Dimensional, Hydrodynamic Hindcast Dataset for the Long Island Sound and New York/New Jersey Harbor Estuaries
Journal of Marine Science and Engineering
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
... e 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. 2 of 22 2 • C above pre-industrial levels, and aims to limit the increase to 1.5 • C, as doing so is expected to significantly reduce risks and the impacts of climate change. Yet, the Northeast US shelf waters have experienced higher warming rates than the global ocean, deduced by the Sea Surface Temperature (SST) satellite record. Pershing et al.  reported that SST rose by 0.30 • C per decade between 1982 and 2013 in the Gulf of Maine. 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  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; ). Over these last few decades, the LIS ecosystem has undergone profound changes. Ocean warming is suggested to be the most important factor associated with the observed shifts in the mean center of biomass in Northeast U.S. fisheries [3,    . However, understanding what controls the observed trends in the Northeast U.S., and how such processes affect the LIS ecosystem, has been limited due to the paucity of available three-dimensional, physical data. In 2013, the New York and Connecticut Sea Grants and the US EPA Long Island Sound Study joined forces to fund a multi-disciplinary project to address this deficiency, spearheading collaborative research involving numerical modelers, climate scientists, and fishery biologists. The work evaluated conditions and identified warming, freshening, and estuarine circulation trends in Long Island Sound over the past three decades. This research also explored how global climate contributes to long-term and inter-annual variability in the LIS physical environment and its Living Marine Resources . This research article, presented at the 14th Estuarine and Coastal Modeling Conference (ECM14, http://ecm.github.io/ECM14/), focuses on the validation and results of a comprehensive, multi-decadal, hindcast simulation performed using the New York Harbor Observing and Prediction System (NYHOPS) hydrodynamic model that generated a continuous, three-dimensional dataset for a coastal aquatic region that includes Long Island Sound and the New York/New Jersey Harbor (NYNJH) Estuaries, between 1981 and 2013. Section 2 describes the data and methods used to set up the multi-decadal hindcast and the data and methods used to validate it for LIS and NYNJH and to have it serve as an open access dataset. Section 3 presents validation results. Section 4 puts the importance of the validation in perspective and discusses identified or verified trends and climatologies based on the validated model. Conclusions are outlined in the last section. Supplementary material in the form of a comprehensive PowerPoint presentation configured in two parts is also provided. An online THREDDS Data Server (http://colossus.dl.stevens-tech.edu/thredds/catalog.html) was set up to serve the NYHOPS model's results in oceanographic NetCDF format over the web using the OPENDAP protocol, enabling open access to daily averaged or monthly averaged time series for all the gridded hindcast physical variables in or over the NYHOPS region (including LIS and NYNJH). Simulated climatologies (mean simulated climate conditions averaged over the three decades of the NYHOPS hindcast period) for two-and three-dimensional fields such as water temperatures and salinities, were also generated, and included in THREDDS. The use of the validated results of the model to research global climate teleconnections to the LIS ecosystem and its living marine resources will be presented in subsequent papers that are presently under preparation. Materials and Methods The completed multi-decadal high-resolution three-dimensional hindcast simulation for LIS and NYNJH was based on a nested modeling concept utilizing two hydrodynamic domains (Figure 1) : The Stevens North Atlantic Predictions model (SNAP) [9-11] and the New York Harbor Observing and Prediction System model (NYHOPS, www.stevens.edu/NYHOPS) [9,11-18]. Both domains were simulated in 3D with the Stevens Estuarine and Coastal Ocean Model code (sECOM) [11,14,19], a derivative of the Princeton Ocean Model . The SNAP model was run first, in a diagnostic mode J. Mar. Sci. Eng. 2016, 4, 48 3 of 22 (clamping temperature and salinity at the initial condition), at its regular 5 km resolution grid for the complete 1979-2013 simulation. SNAP wave and water level results, along with observation-based temperature and salinity fields, were then used to derive NYHOPS offshore boundary conditions and force the NYHOPS prognostic hindcast simulation on its variable-resolution grid (4 km to 25 m horizontal resolution, 10 vertical sigma layers). This is the same nesting concept used operationally for the ensemble-based Stevens Flood Advisory System (www.stevens.edu/SFAS  ).