WP B: Regionalization of Decadal Sea Level projections

WP B aims to establish a scientific basis for obtaining reliable local projections of sea level trends, thus improving quantitative and detailed (high-resolution and high-end) estimates of future coastal sea level changes in the two study regions.

WP B investigates geophysical processes related to coastal sea level changes, such as the relationship and interaction of large-scale ocean circulation with shelf seas and ice sheets on regional and local scale, such as processes due to land movement (subsidence) and lateral inundation (morphodynamics), and downscaling of climate-related sea level information to coastal locations. The information will be merged with local geophysical processes controlling vertical motion of the solid earth and changes in coastline morphology.

New insights from WP B will feed into WP C to improve coastal sea level change scenarios for the selected pilot regions. Massive adaption measures (such as massive embankments) might contribute to changes in extreme sea levels. This, in turn, requires intensive work on explaining past changes in local sea level, including those driven by human interventions.

Challenges that need to be addressed:

To connect regional sea level variability studied in WP A, with coastal impact assessment considered in WP C, major advancements are required in downscaling sea level projections from the basin scale to any coastal location and downscaling uncertainty information due to various remote processes, e.g. ice sheet probability density information.

It further requires progress in understanding the interplay of local sea level changes with extreme sea level events and coastal morphodynamics. To this end, advancements in modelling on regional to coastal scale are prerequisite to dynamical linkages between the open ocean and coastal regions, while considering locally heterogeneous dynamics and non-steric effects of changing sea level over shelf areas (Landerer et al., 2007). We expect that in shelf seas, local circulation dynamics should strongly influence sea level, while extreme events, such as storm surges, can further exacerbate the effect of coastal sea level rise. However, both processes are not quantified, hindering to date connection of basin-scale and regional sea level projections to coastlines.

Downscaling approaches can also involve statistical methods, which might be easier to implement in our study regions, but which, however, typically require an extended database. Similar to the open ocean, improved observational coastal records are needed to better assess shelf sea dynamics and coastal sea level changes, involving tide gauge and altimetric records by (1) extending the altimetric database (e.g., Fenoglio-Marc et al., 2012) to the coast and (2) improving the understanding of natural- and anthropogenic-induced land motion in tide gauge stations (Trisirisatayawong et al., 2011; Wahl et al., 2013).

Of fundamental interest for a reduced uncertainty of sea level changes in our coastal study regions is the local interaction of ocean currents and sea level with ice sheets, which strongly affects sea level projections of remote coastal regions. For this purpose, we need to substantially advance our understanding and modelling of the physical mechanisms of ice sheet changes driven by ice-ocean interactions (Straneo et al., 2013), and adequately represent ice sheet dynamics and changing grounding lines in models (Pattyn et al., 2013), among others.

All coastal sedimentary systems are strongly controlled by and respond to feedbacks between water circulation and sediment transport through various morphological features (Amos et al., 2010). Sea level change and extreme events often induce morphodynamic changes, particularly in deltaic regions (e.g. Unverricht et al., 2013). However, on decadal and longer timescales, morphodynamic models are often limited in reproducing complex morphological evolution (e.g. Chu et al., 2013 and refs. therein). To improve our knowledge on the coastal evolution of our study regions, sediment transport, erosion, deposition and preservation processes as a function of changing sea level need to be quantified and quantitative predictions from morphodynamic models to be improved.

Finally, to advance coastal management in our study regions, it is necessary to improve projections of future sea level extremes, affected by extra-tropical storms (Woodworth et al., 2007) and local mean sea level rise (Dangendorf et al., 2014), which can cause large economic and ecological damage to insufficiently protected coasts (Hallegatte et al., 2011a, b). Estimation of changes in frequency and intensity of storm surges is not straightforward, since they depend on many local parameters. Secular sea level trends will most directly affect peaks in storm surges, however, to what extent they can be added linearly to surge changes (Woodworth et al., 2007) in the study regions needs to be investigated. Previous model results point to a significant increase of storm surge elevations for the continental North Sea coast of 15 to almost 25 cm (Woth, 2005) but whether this also holds for the North and Baltic Seas and for the Indonesian Archipelago is unknown.

Approach:

WP B combines observations and modelling to downscale regional sea level changes to shelf-sea and coastal regions, both dynamically and statistically. It aims to improve our understanding of sea level dynamics and ability to predict or project coastal sea level changes in the two study regions. Work involves regional simulations with model systems incorporating high-resolution coupled atmosphere-ocean-wave models, including tide.

Altimetry databases will be extended to the coast to consistently connect with tide gauge/GNSS observations and solid Earth response models, thus bridging the spatial scales from regional to local, and merging historical long-term records with current sea level monitoring and future predictions. This task will be facilitated by new observation technologies of modern satellite altimetry sensors.

Concurrently, research will target detailed ocean-ice sheet interaction studies to improved understanding of ice sheet mass loss processes, which is demanded by WP A. Concerning observations of ice sheet changes, three fundamentally complementary approaches exist:

  • the geometric approach, primarily based on satellite altimetry
  • the input-output approach, i.e. estimation of of surface mass balance and ice discharge budget using InSAR space techniques
  • the gravimetric approach, using the GRACE and the upcoming GRACE follow-on missions.

Research projects within the SPP Research Area B (WP B):

Research projects that fall within both the Research Areas A and B (WP A/B) are:

In addition, research projects that fall within both the Research Areas B and C (WP B/C) are:

Approach

The work program is structured in four basic topics; work within each topic is expected to be addressed by several working groups as part of the SPP.

Topic I

Coastal sea level projections

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Topic II

Feedback with extreme events and morphodynamics

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Topic III

Sea level - ice sheet interaction

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Topic IV

Coastal sea level information

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