Decadal changes in wave climate and sea level regime: the main causes of the recent intensification of coastal geomorphic processes along the coasts of Western Estonia?

Abstract

Strong erosion of accumulative shores and redistribution of matter has been observed along the practically tideless west coast of Estonia during the last half century. This indicates manifestations of climate change, such as increased storminess and high sea level. The objective of the paper is to presents an analysis of sea level data obtained from the Estonian tide gauges over the period 1842-2008 and to discuss the results of a hindcast simulation of wave conditions in the fetch-limited nearshore location of West Estonia for the period 1966-2006. After adjusting the historical sea level time series to take into account land uplift, the series of mean sea level display an upward trend of between 1.5 and 2.7 mm/yr, and 4-11 mm/yr for annual maximum sea levels. The results for wave climate show some quasi-periodic cycles, including a rise in mean wave height in the 1970s and 1980s, and decrease since 1990. Although both the average wind speed and the wave height show a decrease since 1990s, the annual sea level maxima, as well as the wave maxima continue to increase. Major coastal geomorphic changes seem to occur precisely as a combined result of such relatively infrequent but extreme wintertime wavestorms and storm surges.

Recent Change—Sea Level and Wind Waves

“…Quite large variations in the average wave periods (from about 2.3 s in the mid-1970s to 2.65 s around 1990) were found for selected sites (Suursaar and Kullas 2009b). This is apparently a local effect, because in most of the Baltic Sea the most frequent wave periods and the distribution of the different wave periods are effectively unchanged .…”

“…The local maximum in the Arkona Basin and a rapid increase in simulated wave height in this region may stem from the overestimation of geostrophic wind speed in this part of the basin (see Pryor and Barthelmie 2003). There is a very slow decrease (about 0.01 m s −1 year −1 ) in the annual mean wind speed at Kalbådagrund, Gulf of Finland where numerical simulations indicate very minor change in wave intensity (Suursaar and Kullas 2009b;Suursaar 2010;Soomere et al 2010).…”

“…Hindcast simulations suggest a sawtooth-like behaviour for the 99th percentile, with a gradual increase for 1958-1990 from about 4 to about 5 m, a sudden decrease in 1991-1992 and a subsequent increase (Soomere and Kurkina 2011). Suursaar and Kullas (2009b) noted a negative trend in the 99th percentile near the north Estonian coast and a weak, opposite, gradually positive trend in average wave height. Simulations using the WAM wave model (Komen et al 1994) showed that, unlike for average wave height, there has been a substantial decrease (of about 10 %) in maximum wave height Fig.…”

Influence of seasonal sea ice conditions on hydrodynamic processes and oil spill drift

“…While near Vilsandi (Fig. 1) both high sea level and high wave events are increasing [16], the wave heights are probably decreasing along the northerly exposed North Estonian coast as a result of northward shift of atmospheric pressure systems [7]. Decadal variations in average (a) and maximum (b) values of annual significant wave height data as a comparison between meteorologically forced hindcast and the hindcast with ice mask applied in the periods with real ice cover in the Letipea-Kunda region of the Gulf of Finland.…”

“…Recent vitalization of coastal processes in the West Estonian Archipelago is supposed to occur as a result of increased storm surge and wave heights in one hand [16,17], and more frequent absence of protective ice cover in the last decades in other hand [3]. While near Vilsandi (Fig.…”