Yannis N. Krestenitis

Climate change effects on the marine characteristics of the Aegean and Ionian Seas

This paper addresses the effects of estimated climate change on the sea-surface dynamics of the Aegean and Ionian Seas (AIS). The main aim is the identification of climate change impacts on the severity and frequency of extreme storm surges and waves in areas of the AIS prone to flooding. An attempt is made to define design levels for future research on coastal protection in Greece. Extreme value analysis is implemented through a nonstationary generalized extreme value distribution function, incorporating time harmonics in its parameters, by means of statistically defined criteria. A 50-year time span analysis is adopted and changes of means and extremes are determined. A Regional Climate Model (RegCM3) is implemented with dynamical downscaling, forced by ECHAM5 fields under 20C3M historical data for the twentieth century and the SRES-A1B scenario for the twenty-first century. Storm surge and wave models (GreCSSM and SWAN, respectively) are used for marine climate simulations. Comparisons of model results with reanalysis and field data of atmospheric and hydrodynamic characteristics, respectively, are in good agreement. Our findings indicate that the dynamically downscaled RegCM3 simulation adequately reproduces the present general circulation patterns over the Mediterranean and Greece. Future changes in sea level pressure and mean wind fields are estimated to be small, yet significant for marine extremes. In general, we estimate a projected intensification of severe wave and storm surge events during the first half of the twenty-first century and a subsequent storminess attenuation leading to the resettlement of milder extreme marine events with increased prediction uncertainty in the second half of the twenty-first century.

Simulation and multicriteria analysis in sustainable coastal planning: the case of aquaculture in Thermaikos Gulf, Greece

Mussel aquaculture in Thermaikos Gulf is facing a great challenge to tackle both institutional and production planning aspects. Local stakeholders are concerned about the future design of an efficient and equitable legal planning framework for the aquaculture, as well as about the improvement of production planning in order to optimize the total economic outcome of mussel activity in the area. The present paper focuses on the assessment of alternative production planning decisions, under the assumption that an efficient and socially acceptable institutional framework is already established. To this end, a case-specific decision-making tool is designed aiming to combine simulation modelling and multicriteria analysis. The main interactions between the environmental and cultivation conditions and the socio-economic parameters of the local aquaculture are specified according to a previous modelling effort concerning the long-line mussel farms of the study area. These interactions are then incorporated into a multicriteria model, which is formulated to handle the decision-making problem of selecting the best alternative planning decisions. This is actually a problem of evaluating and choosing the most promising policy options in terms of local society preferences. An integrated approach is followed, by means of an analytic hierarchy process, aiming at analysing the preferences of local community by determining the weights for a specific set of (sustainability) criteria. The relative importance of these criteria is determined through a questionnaire survey among the local stakeholders. The results from this application show that future planning policies should focus on production techniques, which are likely to enhance the quality of mussel production and, at the same time, to minimize the economic risk associated with the local occurrence of Harmful Algal Bloom events.

Modelling Cohesive Sediment Dynamics in the Marine Environment

The inflow of fine sediments in the marine environment affects various processes and has significant socioeconomic and environmental impacts, the most straight-forward of which is related to sedimentation in deltaic and coastal areas. However, fine sediments have the ability to affect solar radiation in the water column and to absorb contaminants on their surface [1,2]. Therefore, fine sedimentary plumes also affect primary productivity and the distribution of pollutants in the column and the seabed. The distinction between fine ( 63μm) sediments is rather general and varies with the type of the sedi‐ mentary matter, but it is a fact that the dominance of inter-particle cohesion forces over grav‐ itational forces varies inversely with the floc diameter. Thus, the effect of cohesion is much more pronounced on the behaviour of clays (diameter <2μm) than of silts (2-63μm); in fact, the development of cohesion in silty clays is mainly due to the clay fraction in the sedi‐ ment [1]. Adhesion diversifies the behaviour of cohesive and sandy sediments in the aquat‐ ic domain, adding further complexities to modelling efforts for fine sedimentary plumes. Their movement is the result of the combined action of various physical processes and forces (Figure 1).