WP2 – High-end Scenarios

Objectives

nicedayforit copiaThe primary goal of WP2 is to provide a representative range of scenarios to be considered within the project with focus on high-end projections for socio-economic (e.g. population, urbanization, development patterns) and physical (global/regional sea level rise, extreme sea levels, storminess and waves) variables. We shall explore new Representative Concentration Pathways (RCP) scenarios, associated with temperature changes up to 6º C, which imply the largest intensification of coastal hazards due to the global and regional sea level rise, changes in extreme sea levels and waves. For socio-economic coastal scenarios we will make use of the new emerging shared socio-economic pathways (SSP). We shall specifically explore those climate change scenarios that imply the largest intensification of coastal hazards and how to identify precursors in climate evolution, looking for consistency in projections, horizons and reliability; we shall identify the timing when climate change will be detectable from regional observations, anticipating when the climate change signal will be sufficiently large to overcome the “noise” of interannual variability. The timing would depend on the pace and size of climate change and it will be different for different evolution scenarios (and for different variables). Therefore this exercise (done previously for temperature and precipitation but not for marine storminess) would provide new tools for detecting which path climate change is following. We shall add, when necessary, semi-empirical models or the more extreme results from some SRES scenarios since the outputs from WP2 will be used in WP1, WP3, WP4, WP5 and WP6.

Following this, the specific objectives of WP 2 are:

• To assemble a representative range of RCP and SSP scenarios to be considered within the project with a particular focus on high-end conditions.

• To develop and implement statistical tools to analyse past scenarios and to allow the generation of future high-end scenarios, including the likelihood of this scenario to manifest

• To downscale physical variables to be used as physical drivers in the rest of WPs for cross-scale assessments

• To downscale socio-economic variables reflecting coastal urbanisation and development patterns to be used in the rest of WPs.

• To develop socio-economic growth projections, specifically for coastal regions, for the range of the above mentioned scenarios.

• To integrate these projections into impact assessment models (for long term and extreme event scales).

Description of work and role of partners

In WP2 we shall prepare a selected set of high end scenarios for physical and socio-economic variables. The downscaling will be physical (using the nested sequence of models described for event scale impact assessment) and statistical (using multiple linear regression for predictors encompassing temperature or pressure gradients-linear and squared- anomalies) and will include a reanalysis of existing simulations to provide a wider range of variables (e.g. higher frequency meteorological fields to properly simulate storm surges and waves under future projections). We shall also carry out a number of dedicated high resolution simulations for the regional cases with a larger information support to look for coastal scale inconsistencies and to provide feedback to the general climate modelling community. We shall focus on scenarios leading to intensification of coastal hazards, including precipitation events that occur during storms and often exacerbate the impact in coastal areas.

We shall also obtain socio economic realisations on a country-scale based on SSPs (considering also the higher rates of growth for population and economy in the coastal zone) and physical projections based on a range of  RCPs such as e.g. those used for AR5. The emphasis will be on the discrepancies apparent when downscaling different variables and how to provide “boundary” feedback from the local/regional to the global scales. We shall

address long-term scale regional sea level changes together with new Representative Concentration Pathways (RCP), associated with temperature changes up to 6º C (e.g. regionalised projections for 4 CMIP5 GCMs and 3 RCPs just submitted for publication by one of the partners). To this we shall add wave and surge effects at an extreme event scale. In both cases we shall discuss with the other 2 climate projects in this call (HELIX and IMPRESSIONS) the possibility of sharing scenarios and the feasibility of using a common core set.

Task 2.1. Scenario selection: set of RCPs, SSPs and other projections (NOC, HZG, CAU, CMCC)

Start: Month 1, End: Month 10 The objective of this task is to select RCP high-end scenarios (highest emission, with likely temperature rise of 6ºC) with concomitant socio-economic scenarios and demonstrate that extensive changes in coastal areas are driven not only by climate change, but they are also highly determined by socio-economic development. This requires the selection of appropriate SSPs and combinations of RCPs with SSPs (Milestone 4). A preliminary list of 5 SSPs have been proposed, but work is on-going to refine these scenarios with the first quantitative projections of key variables becoming available (ISI-MIP database, available at: https://secure.iiasa.ac.at/web-apps/ene/SspDb). SSPs do not include assumptions about mitigation policy and are, thus, independent from RCPs in the sense that the same SSP may lead to different levels of radiative forcing and hence sea-level rise or other physical variables depending on the level of mitigation reached. Use of high-end RCP scenarios will introduce large uncertainties in global sea level projections, given the huge uncertainties involved in the ice-sheet contribution to sea level rise. To address this issue we will assemble alternative high estimates of possible global sea level rise from published studies to define an upper limit, considering also available palaeo-information. This upper limit (scenario independent) will be employed to assess the impact of the highest possible sea level rise by the end of 21st century. Regarding storminess we shall investigate regional variations considering that depleted Arctic summer sea ice alters atmospheric circulation patterns (and thus storm tracks) outside the Arctic, throughout the following months and into the winter in mid-latitudes. In particular areas (e.g. Mediterranean basin) we shall look at the possible shift of mid-latitude storm tracks, which would change the storm features. From here we shall produce a structured set of projections (Deliverable 2.1) by 2100 using initially the RCP4.5, RCP6 and RCP8.5 scenarios. For all variables we shall derive a first set of projections by month 12 to allow starting the impact assessment work and tool generalisation. This will be followed by a refined set of projections by month 24, as indicated in the Tasks description below.

Task 2.2. Regionalised socio-economic projections: collection of downscaled variables for high-end SSPs scenarios (CAU, GCF)

Start: Month 6, End: Month 24

The objective of this task is to provide a set of regionalized socio-economic projections that are consistent with global SSPs, RCPs and regional patterns of development and urbanization (Milestone 5). For many locations it is observed that coastal population and assets are growing faster than the national average trends due to coast-ward migration, coastal industrialization and urbanization. Combinations of specific economic, geographic and historical conditions attract people and drive such migration, particularly in coastal urban areas, where expansion rates are statistically higher than in non-coastal ones. This process is expected to continue in the coming decades, but is difficult to capture in global scenarios, as the drivers of migration and urbanization are complex and variable and their intensity depends on the characteristics of socio-economic development pathways. Using the latest available data on the distribution of current and future global population and assets we will produce (linked to Task 2.1) the first global projections (Deliverable 2.2) for coastal population and assets for different SSPs, specifically accounting for the differential growth rates that many of the world’s coastal regions experience. Based on this we shall develop a set of regionalized socio-economic projections (Deliverable 2.3) for selected (according to our coastal typologies and vulnerability hotspots from WP 1) regions and for a range of SSPs.

Task 2.3. Regionalized physical projections: collection of downscaled variables for high-end RCPs scenarios

Start: Month 6, End: Month 24

In this task we shall address regional sea level rise and extreme events (storms) by 2100. The task will also consider the comparison with other (less unfavourable) scenarios and semi-empirical models. These physical “drivers” are essential for impact evaluation on natural (e.g. the evolution of sensitive coastal ecosystems) and socio-economic (e.g. harbour operability) systems.

Task 2.3.1. Regional sea level projections by 2100 (NOC, HZG, GeoEcoMar, CMCC)

The objective of this task is to provide regional sea level projections that will differ substantially from a global average, with complex spatial patterns resulting from steric variations, ocean dynamical processes, water mass redistribution (contribution from melting of ice sheet and glaciers) and local vertical land movements (glacial isostatic adjustment and deltaic subsidence). Steric/dynamic sea level projections will be based on the latest climate model simulations assembled in the WRCP’s Fifth Coupled Model Intercomparison Project (CMIP5), plus the recent advances in methodology and relative contributions from recent EU projects such  as ICE2SEA. The land ice (glaciers and ice sheets) contribution patterns show a clear gravitational signature, characterised by a sea-level drop near main ice loss regions and above-average sea-level rise at low latitudes. This pattern will begin to dominate the regional sea level change toward the end of the 21st century, especially under the high emission RCP8.5 scenario. We will utilize individual regional projections (Milestone 6) with contributions from Antarctica (which would increase the regional sea level rise in Europe), Greenland (which would decrease sea level rise along the coastal area of Europe) and the special contribution from glaciers. Sea level projections for the Mediterranean and Black Seas are challenging tasks that we shall specifically address in our project, considering regional effects such as the exchanges of Mediterranean and Atlantic waters via the Gibraltar Strait and the extreme scenario results recently obtained in the CIRCE EU research project. Sea level projections for the Black Sea will be calculated as a combination of projected changes in fresh water budget using regional model simulations and water mass exchanges with the Mediterranean Sea via the Bosphorus and the Dardanelles Straits; local sea level projections in the Danube delta area will be corrected for the vertical land movement due to subsidence.

This sub-task will, thus, produce a global map of sea level patterns (Deliverable 2.4) and projections of sea level rise for each RCP scenario and complementary upper limit estimates. This will serve to determine regional patterns under high-end scenarios by 2100 with realistic uncertainties and, for the first time, the corresponding sea level projections for the Mediterranean and Black Seas (Deliverable 2.5).

Task 2.3.2. Regional projections of extreme events by 2100 (CMCC, NOC, HZG, UPC, GeoEcoMar, Deltares)

The objective of this task is to derive global projections of extreme storm surge levels and sea wave heights (eventually period and direction, a novelty for assessing coastal impacts) for selected areas such as the North West European continental shelf, the Mediterranean and the western Black Sea(Milestone 6). Surge and wave projections for each scenario will be provided for the NW European continental shelf (same approach for other European seas) by means of running a full Atlantic wave model and a nested wave plus surge code. We shall also examine extreme events i.e. mid-latitude storms with their change in frequency, intensity and track for the climate model projections using each of the selected high-end scenarios. It will result in an assessment of past events using tracks and meteorological parameters such as wind speed that allow generating robust high-end scenarios (Deliverable 2.4 – Month 12).

We will consider the changing probability of wave events by looking at changes in storminess from the GCM runs under CMIP5 (Task 2.1) and using a combination of dynamic and/or statistical downscaling to make projections of surges and waves on a regional scale. We shall improve our statistical tools to determine probability levels by employing recent results (e.g. MedCORDEX RCM simulations) and extensive databases containing parameterised cyclone systems (at NOOA for Hurricanes from 1851 onward, at JTWC for typhoons/cyclones from 1945 onwards and at GLOSS for high water levels and waves). This will allow a new level of analysis of past extreme events and therefore to generate more robust regional high end scenarios (Deliverable 2.5 – Month 24). For the Black Sea the impact of climate change has been modelled so far by the time horizon 2040, in the Masterplan for the Protection against Erosion of the Romanian Black Sea littoral. Our approach will, thus, provide the first characterization of regional high-end scenarios for that area.