Towards an Integrated Assessment of Sea-Level Observations Along the U.S. Atlantic Coast

Sea levels are rising globally due to anthropogenic climate change. However, local sea levels that impact coastal ecosystems often differ from the global trend, sometimes by a factor of two or more. Improved understanding of this regional variability provides insights into geophysical processes and has implications for coastal communities developing resilience to ongoing sea-level rise. This dissertation conducts an investigation of sea level and its contributing processes at multiple spatial scales. Focusing on primarily interannual time-scales and data-driven approaches, new data sources and technologies are utilized to reduce current uncertainties. First, sea-level trends are assessed over the global ocean and at coastlines using data from the recently launched ICESat-2 satellite. These trends agree well with independent measurements, while also filling observational gaps along undersampled coastlines and at high-latitudes. Next, the spatial focus is narrowed to the U.S. East Coast, which is experiencing exceptionally high rates of relative sea-level rise, largely due to land subsidence. By incorporating new state-of-the-art estimates of land-ice melt, an existing Bayesian hierarchical space-time model is expanded to assess the relative contributions of sea surface height and vertical land motion to 20th century relative-sea level change. Model results confirm previous findings that identified regional-scale geological processes as the primary driver of spatial variability in East Coast relative sea level. By rigorously quantifying uncertainties, constraints are placed on the current state of knowledge with clear directions for future research. Finally, small-scale vertical land motion in Hampton Roads, VA is investigated using the remote-sensing technology of Interferometric Synthetic Aperture Radar (InSAR). Two different data sources and processing strategies are implemented which independently reveal substantial rates of vertical land motion that vary over short spatial scales. The results highlight the importance of vertical land motion in exacerbating negative impacts of relative sea-level rise such as flooding and inundation. Overall, this study leverages new spaceborne sensors, an innovative statistical model, and state-of-the-art processing strategies to enhance our understanding of ongoing sea-level change

Precipitation and Sea Level Rise Impacts on Groundwater Levels in Virginia Beach, Virginia

Global sea level rise (SLR) is one of the most immediate impacts of climate change, and poses a significant threat to low-lying coastal communities worldwide. The metropolitan region of Hampton Roads in Southeastern Virginia is one such community, and one where knowledge surrounding SLR is rapidly accumulating. However, most of the research is focused exclusively on surface water processes despite the presence of a shallow groundwater table closely connected to them. SLR will continue to cause the groundwater table to increase in tidally influenced areas of Hampton Roads, and thereby decrease storage capacity of the unsaturated zone. This study investigates the spatial and temporal response of the groundwater table to SLR and precipitation. We choose a tidal watershed, West Neck Creek, in Hampton Roads was chosen to conduct a conceptual yet realistic simulation of the hydrologic cycle using historical precipitation data with SLR scenarios from 0 m (current) to 2 m in 1 m intervals. Groundwater infiltration from the land surface, recharge, and evapotranspiration are modeled using the Unsaturated-Zone Flow package with MODFLOW-NWT. Groundwater rise is simulated by increasing the stage of the tidal stream that drains the watershed. Precipitation and overland runoff are simulated using the surface water model SWMM. The two models are coupled to permit the exchange of boundary condition values at each time step.An ensemble approach is taken to test model sensitivity to a variety of parameters. The findings of the study demonstrated the potential for the effects of SLR-induced groundwater rise to become a damaging hazard to Virginia Beach communities and ecosystems. Most of the potential damages arose from increased interactions of groundwater levels with subsurface infrastructure. Additional runoff was found to be of lesser concern, because the prevalent soils in West Neck Creek are characterized by slow infiltration rates. The results of the sensitivity analysis provided encouraging results, in that changes in parameters did not have excessively large effects on forcing variables. Overall, this study provides a foundation to guide future scientific and engineering efforts to mitigate and adapt to the increasing threat of SLR-induced groundwater rise

Towards Sustained Monitoring of Subsidence at the Coast Using InSAR and GPS: An Application in Hampton Roads, Virginia

Hampton Roads is among the regions along the U.S. Atlantic Coast experiencing high rates of relative sea level rise. Partly to mitigate subsidence from aquifer compaction, Hampton Roads is injecting treated wastewater into the underlying aquifer. However, the GPS (Global Positioning System) station spacing (∼30 km) is too coarse to capture the spatial variability of subsidence and potential uplift from the injection. We present a cost‐effective workflow for generating an InSAR (interferometric synthetic aperture radar) and GPS combined displacement product. We leverage a live, open‐access archive of InSAR products generated from Sentinel‐1 data. We find an overall subsidence rate of −3.6 ± 2.3 mm/year with considerable spatial variability. The effects of groundwater injection are currently below detection. The workflow presented here is an asset for sustained monitoring of the injection effort and regional subsidence that is applicable along the U.S. coasts for assisting in mitigation and adaptation of relative sea level rise

An Assessment of Regional ICESat-2 Sea-Level Trends

Sea-level rise is an important indicator of ongoing climate change and well observed by satellite altimetry. However, observations from conventional altimetry degrade at the coast where regional sea-level changes can deviate from the open-ocean and impact local communities. With the 2018 launch of the laser altimeter onboard ICESat-2, new high-resolution observations of ice, land, and ocean elevations are available. Here we assess the potential benefits of sea level measured by ICESat-2 by comparing to data from Jason-3 and tide gauges. We find good agreement in the linear rates computed from the independent observations, with an absolute average residual of 3.60 ± 0.03 cm yr−1 between global ICESat-2 and Jason-3 observations at a 1° posting. The recent La Niña is clearly evident in ICESat-2 observations, as well as small-scale features. By demonstrating the quality of the ICESat-2-measured sea level, we provide support for integrating it into the existing suite of sea-level observations

Observation-based trajectory of future sea level for the coastal United States tracks near high-end model projections

With its increasing record length and subsequent reduction in influence of shorter-term variability on measured trends, satellite altimeter measurements of sea level provide an opportunity to assess near-term sea level rise. Here, we use gridded measurements of sea level created from the network of satellite altimeters in tandem with tide gauge observations to produce observation-based trajectories of sea level rise along the coastlines of the United States from now until 2050. These trajectories are produced by extrapolating the altimeter-measured rate and acceleration from 1993 to 2020, with two separate approaches used to account for the potential impact of internal variability on the future estimates and associated ranges. The trajectories are used to generate estimates of sea level rise in 2050 and subsequent comparisons are made to model-based projections. It is found that observation-based trajectories of sea level from satellite altimetry are near or above the higher-end model projections contained in recent assessment reports, although ranges are still wide. &nbsp;</p

Localized uplift, widespread subsidence and implications for sea level rise in the NYC Metropolitan Area

&lt;p&gt;Regional relative sea level rise is exacerbating flooding hazards in the coastal zone. In addition to changes in the ocean, vertical land motion (VLM) is a driver of spatial variation in sea-level change that can either diminish or enhance flood risk. Here we apply state-of-the-art Interferometric Synthetic Aperture Radar (InSAR) and global navigation satellite system (GNSS) time-series analysis to estimate velocities and corresponding uncertainties at 30 m resolution in the New York City Metropolitan Area, revealing VLM with unprecedented detail. We find broad subsidence of 1.6 mm/yr consistent with glacial isostatic adjustment to the melting of the former ice sheets, and previously undocumented hotspots of both subsidence and uplift that can be physically explained in some locations. Our results inform ongoing efforts to adapt to sea-level rise and reveal points of VLM that motivate both future scientific investigations into surface geology and assessments of engineering projects.&lt;/p&gt;&lt;p&gt;Funding provided by: NASA Headquarters&lt;br&gt;Crossref Funder Registry ID: http://dx.doi.org/10.13039/100017437&lt;br&gt;Award Number: &lt;/p&gt

Vertical Land Displacement Rates and Uncertainty in Hampton Roads, VA [Dataset]

These data contain vertical rates (mm/yr) of surface land displacements and their associated uncertainties from 2015-03-15 to 2019-06-01. They are associated with Buzzanga, B. A., Bekaert, D. P. S., Hamlington, B. D., and Sanga, S. (2020), Towards Sustained Monitoring of Subsidence at the Coast Using InSAR and GNSS: An Application in Hampton Roads, Virginia submitted to Geophysical Research Letters

Toward Sustained Monitoring of Subsidence at the Coast Using InSAR and GPS: An Application in Hampton Roads, Virginia

Hampton Roads is among the regions along the U.S. Atlantic Coast experiencing high rates of relative sea level rise. Partly to mitigate subsidence from aquifer compaction, Hampton Roads is injecting treated wastewater into the underlying aquifer. However, the GPS (Global Positioning System) station spacing (∼30 km) is too coarse to capture the spatial variability of subsidence and potential uplift from the injection. We present a cost‐effective workflow for generating an InSAR (interferometric synthetic aperture radar) and GPS combined displacement product. We leverage a live, open‐access archive of InSAR products generated from Sentinel‐1 data. We find an overall subsidence rate of −3.6 ± 2.3 mm/year with considerable spatial variability. The effects of groundwater injection are currently below detection. The workflow presented here is an asset for sustained monitoring of the injection effort and regional subsidence that is applicable along the U.S. coasts for assisting in mitigation and adaptation of relative sea level rise