Abstract. Tools for estimating probabilities of flooding hazards caused by the
simultaneous effect of sea level and waves are needed for the secure planning
of densely populated coastal areas that are strongly vulnerable to climate
change. In this paper we present a method for combining location-specific
probability distributions of three different components: (1) long-term mean
sea level change, (2) short-term sea level variations and (3) wind-generated
waves. We apply the method at two locations in the Helsinki archipelago to
obtain total water level estimates representing the joint effect of the still
water level and the wave run-up for the present, 2050 and 2100. The
variability of the wave conditions between the study sites leads to a
difference in the safe building levels of up to 1 m. The rising mean
sea level in the Gulf of Finland and the uncertainty related to the
associated scenarios contribute notably to the total water levels for the
year 2100. A test with theoretical wave run-up distributions illustrates the
effect of the relative magnitude of the sea level variations and wave
conditions on the total water level. We also discuss our method's
applicability to other coastal regions.
Abstract. We analyse changes in meteotsunami occurrence over the past century (1922–2014) in the Gulf of Finland, Baltic Sea. A major challenge for studying these short-lived and local events is the limited temporal and spatial resolution of digital sea level and meteorological data. To overcome this challenge, we examine archived paper recordings from two tide gauges, Hanko for 1922–1989 and Hamina for 1928–1989, from the summer months of May–October. We visually inspect the recordings to detect rapid sea level variations, which are then digitized and compared to air pressure observations from nearby stations. The data set is complemented with events detected from digital sea level data 1990–2014 by an automated algorithm. In total, we identify 121 potential meteotsunami events. Over 70 % of the events could be confirmed to have a small jump in air pressure occurring shortly before or simultaneously with the sea level oscillations. The occurrence of meteotsunamis is strongly connected with lightning over the region: the number of cloud-to-ground flashes over the Gulf of Finland were on average over ten times higher during the days when a meteotsunami was recorded compared to days with no meteotsunamis in May–October. On a monthly level, statistically significant differences between meteotsunami months and other months were found in the number of CG flashes, convective available potential energy (CAPE), and temperature. Meteotsunami occurrence over the past century shows a statistically significant increasing trend in Hamina, but not in Hanko.
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