Bridging the 100 km gap: improving coastal sea-level change projections

Despite the serious impacts likely to occur to coastal communities from future mean sea-level rise (via enhanced storm-surges and tidal flooding), there remains significant uncertainty in projections. These are due to limitations in current coupled atmosphere-ocean climate models’ ability to replicate coastal sea level behaviour at spatial scales of less than 50km and time scales of less than a decade (Zanna et al. 2019).
Short-term (multiple years to decades) influences from atmosphere-ocean interactions can cause local, rapid sea-level change (Dangendorf et al. 2021). Additionally, the transition from the open-ocean to the coastal zone affects sea level through changes in sea-floor topography and coastline geometry, the conversion of ocean currents into near-shore currents as well as shoreline composition, river outflow position and sediment movement (Woodworth et al. 2019).

Few of these coastal factors are accounted for in coupled atmosphere-ocean models so it is important to address this gap (in resolution, processes, and timescale) to provide decision-makers with the best possible projections of local sea-level change (Ponte et al. 2019).

The aim of this project is twofold:
1. To develop an empirical model that relates open-ocean to coastal sea-level change via various climate factors using a mixture of observations and model output.
2. To apply the model to climate projections to create new coastal sea-level projections.

The project will develop a model through analysis of observations including coastal- and open-ocean satellite altimetry, in-situ tide gauges, atmosphere (weather and climate) re-analysis products, and coupled atmosphere-ocean models (CMIP6). Similar efforts to this have applied the principle of pattern scaling SSH to global ocean climate factors (e.g., Fernandez-Bilbao et al. 2015) though without any focus on the coastal zone or embedding atmospheric climate factors.

The study will initially focus on the Northwest European shelf due to the variety of open-ocean to coastal settings it offers, high quality observations (for model development) and high-resolution downscaled models (for comparison). There is also flexibility in the project for the student to explore a particular aspect in detail, such as advanced investigation of climate model fidelity, shoreline interactions, multi-scenario projections, or applications of such an approach in less data-rich areas such as along coastlines of developing countries.
Beyond the supervisory group, the student will benefit from advice and engagement with Dr Chris Piecuch (Wood Hole Oceanographic Institution, US).

Click on an image to expand

Image Captions

Schematic illustrating some of the problems faced modelling coastal sea-level change with existing coupled-climate models


Compare historical sea-surface height change (CMIP6 models) with satellite altimetry (observations), and climatology (CMIP6 models) with climate re-analyses (observations).
Develop a statistical model to evaluate the relationship between open-ocean and coastal sea-level observations that embeds common climatological factors.
Apply statistical model to climate model projections to enhance existing sea-surface height change projections. Test against dynamically downscaled ocean model simulations under the same projected climate forcing.

Project Timeline

Year 1

Modelling and data-handling training with supervisory team.
Literature review to evaluate current approaches to connect open-ocean to coastal sea-level, and establish underlying drivers of monthly to multi-annual sea-level change response in a NW European context.
Initial evaluation of climate model output – post-processing and analysis.

Year 2

Intercomparison of climate model output with observations
Model development of observational sea-level and climate factors to connect open-ocean to coastal locations.
Attend international conference and present research.
Write draft research paper for journal submission.

Year 3

Model testing and application to climate model output and comparison to physical downscaled datasets.
Further investigation along lines of particular interest to student as outlined in the Overview.
Draft thesis chapters.
Attend international conference and present research.

Year 3.5

Finalise thesis chapters
Thesis submission

& Skills

The student will receive bespoke training on model creation, processing, analysis and evaluation of sea level and atmospheric model and observational datasets, physical oceanography, and atmospheric climatology from the supervision team. This will include software training in Matlab, Python or R.
Additional numerical modelling and data-manipulation skills will be provided via training workshops (e.g., WRCP workshops, NCAS climate modelling summer school), and national/international workshops with this focus (e.g., CLIVAR, Delft Sea-Level Summer School).
The student will also develop a network of national and international collaborators in the general study area. The student will also attend and contribute to the programme of regular departmental seminars and discussion groups as well as National and International conferences to support their general development as a scientist. The student will be encouraged to write scientific papers for publication during their PhD. This will be a major benefit to their career, and they will be well supported through this process by the experienced supervisory team
The student will also have the opportunity provided by a broad range of skills training provided in-house at Durham through the award-winning Career and Research Development (CAROD) group (thesis writing, writing for publication, presentation skills, enterprise skills etc.) and from the range of environmental science training provided as part of the IAPETUS Doctoral Training Partnership framework.

References & further reading

Dangendorf, S., Frederikse, T., Chafik, L., Klinck, J.M., Ezer, T. and Hamlington, B.D., 2021. Data-driven reconstruction reveals large-scale ocean circulation control on coastal sea level. Nature Climate Change, 11(6), pp.514-520.
Bilbao, R.A., Gregory, J.M. and Bouttes, N., 2015. Analysis of the regional pattern of sea level change due to ocean dynamics and density change for 1993–2099 in observations and CMIP5 AOGCMs. Climate Dynamics, 45(9), pp.2647-2666.
Ponte, R.M., Carson, M., Cirano, M., Domingues, C.M., Jevrejeva, S., Marcos, M., Mitchum, G., Van De Wal, R.S.W., Woodworth, P.L., Ablain, M. and Ardhuin, F., 2019. Towards comprehensive observing and modeling systems for monitoring and predicting regional to coastal sea level. Frontiers in Marine Science, 6, p.437. https://doi.org/10.3389/fmars.2019.00437
Woodworth, P.L., Melet, A., Marcos, M., Ray, R.D., Wöppelmann, G., Sasaki, Y.N., Cirano, M., Hibbert, A., Huthnance, J.M., Monserrat, S. and Merrifield, M.A., 2019. Forcing factors affecting sea level changes at the coast. Surveys in Geophysics, 40(6), pp.1351-1397.
Zanna, L., Brankart, J.M., Huber, M., Leroux, S., Penduff, T. and Williams, P.D., 2019. Uncertainty and scale interactions in ocean ensembles: From seasonal forecasts to multidecadal climate predictions. Quarterly Journal of the Royal Meteorological Society, 145, pp.160-175.

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