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Climate Change Impacts on Cities in the Baltic Sea Region  

Sonja Deppisch

While not all projected climate change impacts are affecting especially and directly at all the cities of the Baltic Sea region (bsr), including its basin, those cities expect very different direct as well as indirect impacts of climate change. The impacts are also a matter of location, if the city with its built structures and concentration of population is located in the northern or southern part of this basin, or more inland or directly at the coast. As there are many different definitions in use trying to determine what a city is, also in the different national contexts of the bsr, here it is cities in the sense of being human-dominated densely populated areas, which are also characterized by higher concentrations of built-up areas, infrastructure, and soil-sealing as well as socioeconomic roles than rural settlements are. Those characteristics render cities also especially vulnerable to climate change impacts while there are some opportunities arising too. There are many studies on climate change impacts on the Baltic Sea itself as well as on the various ecosystems, but the studies on the observed as well as potential future impacts of climate change on cities are disperse, many are also of a national character or concentrating on a small number of cases, leaving some cities not well studied at all. This renders an all-encompassing picture on the cities within the bsr difficult and even more complicated as every city provides a mix of built-up and open structures, of socioeconomic structure and role in a region, nation-state, or even on an international level, and further characteristics. Their urban development is dependent on manifold various interdependencies as well as climatic and nonclimatic drivers, such as, to name just a few diverse examples, urban to international governance processes, or topography and location, or also different socioeconomic vulnerabilities within the Baltic Sea basin. Accordingly every urban society and structure provides specific exposure, vulnerabilities, and adaptive capacity. Generally, the cities of the bsr have to deal with the impacts of temperature rise, natural hazards, and extreme events, and, depending on location and topography, with sea-level rise. With reference to temperature rise and the increase of heat waves, it is important to consider that cities of a certain size within the Baltic Sea basin contribute to their own urban climatic conditions and provide already urban heat islands. Also, urban planning and building facilitated by local political decisions contribute to the extent of urban floods as well as their damage, as these are regulating, for example, the sealing of soils or new built-up areas in flood-prone zones.


Historical Documents as Proxy Data in Venice and Its Marine Environment  

Dario Camuffo

The environmental history of Venice over the last millennium has been reconstructed from written, pictorial, and architectural documentary sources, used in a synergistic way. The method of transforming a document into an index and then into calibrated numerical values according to an international system of units has been applied in the case of Venice and its geographical and climate peculiarities. Because frost constituted a dramatic challenge for the city, a series of severe winters is well documented: The city was sieged by ice, meaning Venetians had to cross the ice transporting food, beverages, and wood for burning in carts, as recorded in written reports and visual representations. The sea level in the 18th century has been reconstructed based on paintings by Canaletto and Bellotto, who took advantage of a camera obscura to precisely draw the views of the city and its canals.. These paintings accurately represent the green algae belt that corresponds to the level of soaking created by marine waters at high tide. This has made it possible to measure how much the green algae (and therefore the seawater) has risen since the 18th century. Similarly, a painting by Veronese has enabled the reconstruction of sea level rise (SLR) since 1571. Another useful proxy is the water stairs of the Venetian palaces. These were originally built to access boats and are now (almost) totally submerged and covered with algae. As the sea level rose, these steps became submerged underwater. The depth of the lowest step is therefore representative of how much the sea level rose after the stair was built. This proxy has allowed the relative sea level since 1350 to be reconstructed, and an exponential trend in the rising of the sea level has been identified. Venice has at times been flooded by seawater, including tsunamis at the beginning of the second millennium. A long series of sea floods due to storm surges triggered by particular meteorological situations shows that the flooding frequency is related to the exponential SLR. In the 1960s, there was a sharp increase in frequency of flooding, which coincided with the digging of deep and wide canals, excavated to allow the passage of tankers. This increased the exchange of water between the sea and the lagoon. Proxies based on archaeological remains, as well as geological-biological cores extracted from the coastal area and dated with isotopic methods, cover long time periods; the longest record reaching 13 ka BP. However, the time resolution is reduced, thus providing good data for physical geography purposes.


Regional Sea Level  

Thomas Wahl and Sönke Dangendorf

Sea level rise leads to an increase in coastal flooding risk for coastal communities throughout the world. Changes in mean sea level are caused by a combination of human-induced global warming and natural variability and are not uniform throughout the world. The key processes leading to mean sea level rise and its variability in space and time are the melting of land-based ice and changes in the hydrological cycle; thermal expansion due to warming oceans; changes in winds, ocean currents, and atmospheric pressure; and, when focusing on the relative changes between the land and the ocean, any vertical motion of the land itself (subsidence or uplift). In addition to the change in mean sea level, which is the main climatic driver for changes in coastal flooding risk in most regions, additional changes in tides, storm surges, or waves can further exacerbate, or offset, the negative effects of mean sea level rise. Hence, it is important to analyze, understand, and ultimately project the changes in all of these sea level components individually and combined, including the complex interactions between them. Advances in sea level science in the 21st century along with new and extended observational records including in situ and remote sensing measurements have paved the path to being able to provide better and more localized information to stakeholders, particularly in the context of making decisions about coastal adaptation to protect the prosperity of coastal communities and ecosystems.


Two Millennia of Natural and Anthropogenic Changes of the Polish Baltic Coast  

Andrzej Osadczuk, Ryszard Krzysztof Borówka, and Joanna Dudzińska-Nowak

Changes of the coast are a net result of morphodynamic processes driven by changes in external conditions. Morphodynamics can be understood as feedback between shore topography and hydrodynamics, the latter including bedload transport, which alters the morphology of the coast. The evolution of a marine coast can take various pathways depending on the time scale, shoreline length, geological setting, tectonic underpinnings, type and availability of sediments in the nearshore zone, sea level changes, intensity of waves and currents, and the influence of the adjacent land masses. A spatio-temporal approach (processes of millennial, decadal, annual, and seasonal change) is particularly important for coastal areas built of erosion-prone, poorly consolidated glacial and postglacial deposits. This is the case of the southern Baltic Sea coast where the shore has been and continues to be impacted by geological processes, climatic factors, and anthropogenic activities. The processes involved are shaped primarily by external factors such as wind–wave action, currents, storm surges, precipitation, winter ice cover, and gravitational mass movements. The shoreline response to climate change depends on both the nature of the change and the coastal zone characteristics. Long-term climate changes result in sea level changes. The sea level rise resulting from global warming enhances coastal erosion, particularly where the shore is built by poorly consolidated rocks and deposits. Coastal zones are usually very sensitive to all the external forces, therefore climate change will most likely be the strongest driver and will be the first to impinge on the coast, whereas the most distant changes in the oceans may produce effects delayed by decades or even centuries.