Work Package 4: Future Scenarios

Work package number: 4
Work package coordination: 2, 5
Work package title: Future Scenarios
Participant id: 1, 2, 3, 5, 6

Objectives

The objectives of workpackage 4 are to:

• Utilize hydrodynamic and NPZD models to forecast changes in the physical and lower-trophic level structure of the North Sea between 2010 and 2100 under different IPCC and eutrophication scenarios.
• Employ multispecies models within future scenarios to estimate the strength and impact of interactions among upper trophic levels and top-down forcing based upon a variety of exploitation strategies.
• Explore the response envelopes depicting the likely outcome of various scenarios of climate- (IPCC) and anthropogenic- (eutrophication and exploitation patterns) drivers on key components and the structure of the future North Sea ecosystem.
• Provide indication of the level of process uncertainty in these approaches and recommend future research actions required to advance forecasts of marine ecosystem change. 

Background

Furthering the understanding of the magnitude and direction of future changes in the ecosystem structure and function of the North Sea ecosystem requires as a first step the regional down-scaling of IPCC scenarios to allow the simulation of future ocean physics and lower level ecosystem processes (NPZD). To expand the biological predictions beyond the bulk variables from these ecosystem models correlation equations as estimated in WP3 come into play. From the future physical data, informed proxies derived in WP3 will be used to assess potential future population levels of a number of key players. This will also include predictions of distribution ranges based on eco-physiological rates and limits and the distributions of preferred and realized habits as observed in the past. For the prediction of the higher trophic levels, correlations between simple and informed proxies and hydrography will be used to generate future envelops of recruitment levels. These serve as input to an SMS scenario run, which starts with the last year of observed population sizes and involves the investigation of alternative exploitation scenarios. The mortality levels from food web interactions and fishing scenarios will translate the recruitment envelops into likely population level envelops.

Description of work

Task 4.1 Regional Hydrodynamic Forecasts

Utilize hydrodynamic models driven by IPCC scenarios to forecast future hydrodynamic features within the North Sea and adjacent areas. For this task the results of EU-project ENSEMBLES will be employed in order to provide the meteorological forcing fields. These data are available for the period 1950 to 2100 having a spatial resolution of 0.22° (ca. 50 km) and covering the entire Northwest-European Shelf to 73°N. The reference period from 1970 to 2000 will be used for validation and calibration whereas for the latter period different IPCC scenarios are available from The Max-Planck-Institute for Meteorology.

For this project we will use two of the IPCC scenarios, i.e., A2 (most pessimistic) and B1 (most optimistic). For both scenarios it is intended to run time-slice experiments with available hydrodynamical models each of a length of 10 years for the periods 2040 to 2050 and 2090 to 2100 generating physically based proxies. These hydrodynamical models will have a resolution of less than 10 km and will run in a fully prognostic mode also for temperature and salinity. The parameters which will be provided to the other sub-projects are all hydrographic and hydrodynamic quantities as well as deduced parameters like thermocline depth or flushing times, with a focus on which of these are of major relevance for the ecosystem dynamics.

Task 4.2 Eutrophication

Using the hydrodynamic forcing estimates produced in Task 4.1 (3D velocity, temperature and salinity fields) several future eutrophication scenarios will be calculated using the ecosystem models (e.g. ECOHAM4) with the main focus on external nutrient inputs and their impacts on the lower trophic levels of the North Sea, especially on phytoplankton concentration, primary production, amounts of sinking detritus and oxygen deficiency events. The future scenarios will mainly focus on the reduction of riverine nitrogen and phosphorus loads and the linkage to precipitation levels but also projections of atmospheric nitrogen deposition will be included. Taking into account that the EU commission and OSPAR have developed guidelines for nutrient load reduction, reduction scenarios should build onto the results of recent OSPAR workshops on eutrophication and modelling of nutrient input reduction scenarios. These scenarios are based on differentiated reduction aims for

1. the different nutrients nitrogen and phosphorus, and
2. for the different North Sea countries.

Applying different ecosystem models for the North Sea the range (and uncertainty) of possible future ecosystem changes can be assessed.

Task 4.3 Higher trophic levels and exploitation patterns

In combination with information on the range of future recruitment levels available for a number of key species from IPCC-based correlations with hydrography, multi-species models (SMS) will be used to translate these into a corresponding range of likely stock sizes. The main advancement will be to utilize climate-driven recruitment levels of different species that reflect the expected atmospheric forcing conditions. Since the outcome will also strongly depend on assumptions about future fishing practice, single and multi-species models will test a number of currently discussed management strategies (e.g., harvest control rules) for a number of key species.

The recovery of the North Sea cod stock is currently a main goal in the application of such strategies and the likely success of HCR approaches will be investigated given IPCC-based recruitment predictions. The predicted composition of the fish assemblage will also yield some general indications about the structure of the plankton, which will be exposed to different predation pressures and scenarios depending on the dominance of specific components of the fish assemblage.

Task 4.4 Scenario forecasts of North Sea ecosystem structure

From the predicted hydrographic data fields species and group specific proxies will be extracted and applied to predict the population levels of the respective species and groups. Through the application of different climate, eutrophication and upper trophic level scenarios indication will be available about the range of response. The rapidity of change in the North Sea system via re-colonization (advection and range shifts / expansion) and changes in internal dynamics will be assessed.

Task 4.5 Synthesis

The different pieces of evidence from the various approaches to response prediction will be integrated into a more holistic picture of the likely future state of the North Sea ecosystem. Emphasis will be placed on the consideration of the process uncertainties (mainly model parameterisations, food web structures, uncertainties in correlations between biological and physical variables etc ) associated with these predictions.