Bridging the 100 km gap: connecting open-ocean to coastal sea-level change to improve local sea-level projections.

Overview

The most recent IPCC report (AR6, 2021) states that the rate of global mean sea-level rise has increased from 1.3 mm yr-1 between 1901 and 1971 to 3.7 mm yr-1 between 2006 and 2018 and that the main driver is very likely to be human influence. Rates are predicted to increase to 15 mm yr-1 by the end of the century (Oppenheimer et al., 2019) with serious implications for the severity and frequency of coastal flooding. However, there are significant uncertainties in these predictions partly due to the inability of climate models to resolve sea-level change at the coast. This coastal gap (of up to 100 km in some climate models) needs to be addressed in order to provide decision-makers with the best possible projections of local sea-level change.
Although most of the big stories around future sea-level change centre on the future contributions from Antarctic and Greenland ice sheets, short-term (multiple years to decades) influences from atmosphere-ocean interactions will cause local, rapid sea-level rise affecting flood frequency and severity leading to significant coastal impacts (Dangendorf et al. 2021). In addition, 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 factors unique to particular coasts such as shoreline composition, river outflow position and sediment movement (e.g. Woodworth et al. 2019).
Since none of these factors are accounted for in coupled atmosphere-ocean models it is important to understand what sea-level projections could be missing at the coastal level (e.g. Zanna et al. 2018). However, this relies on developing a clear method to evaluate the relationship between open-ocean to coastal-ocean signal in the observational records through underlying climate factors (e.g., atmospheric forcing), and evaluating the ability of climate models to simulate larger scale atmosphere-ocean behaviour (Ponte et al. 2019).
Considering these points, the aim of this project is twofold. 1. To develop a 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 in order to improve coastal sea-level projections.
The project will utilise the latest generation of climate models as used in the latest IPCC report (CMIP6 – Eyring et al. 2016) and a mixture of observations including coastal- and open-ocean satellite altimetry, in-situ tide gauges, and atmosphere (weather and climate) re-analysis products. It is expected that the study will have an initial UK emphasis partly due to the variety of open-ocean to coastal settings it offers and high quality observations. 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 Matt Palmer (Sea-level and Ocean Heat content lead at UK Met Office).

Methodology

Use statistical and data-handling methods to post-process climate model output over historical period (post-1850?) to account for drift, internal variability, and model suitability.
Use numerical methods to compare historical dynamic sea-level change (models) with satellite altimetry (observations), and climatology (models) with climate re-analyses (observations).
Develop a physically-based, 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 thereby obtaining coastal dynamic sea-level projections. [Test against dynamically downscaled ocean-dynamic simulations]

Project Timeline

Year 1

Statistical 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 UK context.
Initial evaluation of climate model output – post-processing and analysis.

Year 2

Intercomparison of climate model output with observations
Statistical model development of observational sea-level and climate factors to connect open-ocean to coastal locations for UK.
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 for European Shelf Seas (e.g. Hermans et al. 2021).
Further investigation along lines of particular interest to student as outlined in Overview.
Draft thesis chapters.
Attend international conference and present research.

Year 3.5

Finalise thesis chapters.
Thesis submission.

Training
& Skills

The student will receive bespoke training on science, model creation, processing, analysis and evaluation of sea level, 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 online 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. https://doi.org/10.1038/s41558-021-01046-1
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
Oppenheimer, M., et al. , 2019: Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, et al. (eds.)], Section 4.2.1.5. In press.
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. https://doi.org/10.1007/s10712-019-09531-1
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. https://doi.org/10.1002/qj.3397

Further Information

Please get in touch to discuss the project further and your potential application:
Luke Jackson
luke.p.jackson@durham.ac.uk

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