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Storminess and environmentally sensitive atlantic coastal areas of the European Union

Risultati finali

Given that coastal settings vary greatly, and that as demonstrated, the response of individual areas to storms varies according to a range of factors, the most relevant aspect of the results obtained in this contract is the development of a database of storms from which information can be gained for coastal zone management, associated with information on the vulnerability of coastal areas to storminess effects. The CODACS database as presently developed contains a considerable amount of information on storms from as early as 1500 across the entire Atlantic coastline of the European Union. Plainly, the database does not contain all available information for all areas, but has capacity and flexibility to accept information as obtained. Studies of individual environmentally sensitive coastal areas outlined in the report provide a context for assessment of the vulnerability of coastal areas, but it is emphasised here that a major finding of this contract is the considerable variability of the susceptibility of a given coastal area to storminess impact. The resilience of a coastal area to the effects of storms is very much site-specific and this is emphasised in the findings outlined here, especially by contractors 01, 02, 04 and 05. Indeed, with the observation that susceptibility is so variable, the local variability of resilience is emphasised. Contractor 03 made linkages between CODACS and former EU coastal databases, such as CORINE-Coastal Erosion.
Geological work for this objective was undertaken by all Contractors. Along the Atlantic coastline of Scotland, two localised episodes of sand blow early in the period involved were succeeded by a major and apparently continuous episode from circa 900cal. AD that had ended by circa 1800 cal. AD (although radiocarbon dating control is debatable for the last 200 years). This episode involved predominantly W-NW winds and could have ended later in N areas than in areas to the S, indicating a possibly progressive decline in storminess in southerly areas throughout the period, with a reduction in storminess across the whole area after circa 1800. Along the coastline of NW France, finding that although evidence of late Holocene storms exists, no chronological framework could be produced. Episodes of storm-induced wash-over events along barriers in the Algarve region of southern Portugal between 1270 and 410 BC were identified which appear to become younger along the coast towards the west. In very general terms, it seems that stratigraphical evidence of storminess along the Atlantic coast is probably better preserved in northern locations where the accumulation of peats and gyttjas in coastal locations provides a stratigraphical and dating framework for the study of sediments deposited during storm activity. These areas show evidence that episodes of relative sea level rise may be associated with storminess. From historical and instrumental records, there appears to have been an exceptional period of storminess in Scotland centred upon 1810-1820 AD at Edinburgh, although Atlantic coast records do not extend as early as that. Subsequent periods of exceptional storminess on the Atlantic coast of Scotland occurred during the last three decades of the nineteenth century, as well as in the late 1920s and 1940s, and from the 1970s to the present. Relating these episodes to the North Atlantic Oscillation (NAO) index it appears that whilst the present increase in storminess is associated with a strongly positive NAO index, other storminess episodes are not so strongly correlated. Broadly, storminess episodes can be related to very different synoptic climatologies, and it is suggested that this may reflect varying amounts of sea ice cover in the N Atlantic. In England and France study of surge values for the Brest and Newlyn tide gauges discloses episodes for 1883-5, 1905-8, 1921-2/5, 1930-2, 1952-5, 1961-7, 1974-80 and 1985-6. A strong 12-14 year periodicity. Broadly, surge trends fell in 1880-1940, then rose after 1940, although present levels have not yet exceeded those recorded in the early 1880s and mid 1900s. Documentary records of 577 storms for Ireland over the period 1500-1995 indicates peaks of storm activity from 1730-1749, 1810-1849, 1930s, 1960s and since 1990. Although this refers to Ireland as a whole, Atlantic coast storms are similar in trends, and those storms recorded before 1700 are largely from the Atlantic coast. Historical records for the Portuguese NW coast for 1865-1992 and for the Azores for 1840-1998, show increasing storm intensity but similar storm duration in the former and overall increasing storm intensity in the latter except for the periods 1840-1880 and 1925-1980 respectively. Comparing this data with variations in the NAO indicates that for Portugal, NAO variations can be a proxy for storminess. Historical and instrumental records of storminess were collected from all contractors in the project's Comprehensive Database on Coastal Storms (CODACS) developed by Unive4rsity College Cork working with the other contractors on the project. The structure of CODACS is outlined in Part 2 of this plan.
The geological work undertaken produced only a partial picture of storminess change over the last 2,000 years, indicating a possible movement of storminess impact westwards along the southern coast of Portugal and northwards along the Atlantic coast of Northern Ireland and the western islands of Scotland during the period involved, together, with a possible increasing dominance of northerly gales towards the present. It has been observed that the changing impact of storminess is probably related to relative sea level change and that sea level movements need to be taken into account in these assessments. In addition however, the availability of sediment is an important factor modulating the impact of storminess in different areas. From documentary records, it appears that episodes of enhanced storminess along the Atlantic coastline vary greatly according to past records. Storminess appears to have increased both in the Azores and on the mainland of Portugal to the present day, whilst to the north in France, storminess is increasing in the present century, whilst in Ireland there have been a number of peaks of storminess since circa 1700 with an increase in the last decade to the present and in Scotland a number of peaks have occurred since circa 1750 with again an increase in the last decade. The relationship between storminess and the NAO is a complex one and whilst present storminess is associated with the strongly positive NAO storminess episodes in the Nineteenth century were not. These observations should be set against a further factor in the impact of storminess, namely the movement of the land surface, which is however decreasingly effective in isostaticly effected areas in the north of the Atlantic coastal zone.
In Scotland during the last 2,000 years at least, dune systems have moved inland, notably in areas with a NW-N exposure. The seaward margin of these dune areas has however responded in a more complex way, with sediment supply and near-shore bathymetry interacting with exposure to determine coastal response to storminess. Documentary and instrumental studies have emphasised the highly localised effects of storms whilst stressing the ability of extreme events to achieve considerable feats of sediment transport and erosion. To the south of Ireland, work disclosed storminess impact on dune-fringed coasts was also examined. This wave processes using a 2D numerical model generating wave propagation simulations for eleven sites. The vulnerability of each site to storm winds from different quadrants was assessed. It is observed that major erosional events require the centre of an extra-tropical cyclone (often a former tropical hurricane) to be close to the coastline to lift the focus of wave attack to a supra-tidal level as well as generate steep local waves. This process is less effective where the storm is migrating rapidly, and is out of phase with semi-diurnal tidal elevation relative to storm impacting at a specific site. Analysis of high quality wind data from a series of coastal observations along the Atlantic fringe of Europe was undertaken enabling the identification of extra-tropical cyclones and the detection of storms. The GTECCA database was used as a primary data source. Detailed numerical analyses of this and other data sources were undertaken. In particular new records analysis of three European margin meteorological stations in Ireland was established. Over the period 1965-1994, a cyclical behaviour in storminess was observed for the area as a whole in phase with the NAO cyclicity during the same period. This was established at a quasi-decadal time scale. The Principal Cyclone Track in the North Atlantic seem to have shifted northward during the instrumental period in parallel to a change in the seasonality of storms. In Ireland storms in the winter months appear to have become more intense and less frequent with calmer summers. Determination of extra-tropical cyclone tracks was undertaken, in addition to determination of the mean duration and central pressure changes for these systems, showed that the deepest pressures are recorded in the most northerly zone. Studies of Portugal and France show that storms play a major role in barrier development and coastal change, although the response of the barriers is complex.