Tarmo Kall

Geodetic and Geophysical Repeated Measurements in Geodynamic Monitoring Networks of Estonia

Repeated measurements were started in the first Estonian geodynamic network — the Poltsamaa-Lelle geodynamic line in 1961. Three more geodynamic networks were established in the 1970s: in Navesti (Central Estonia), in Viru-Nigula (North—East Estonia) and in Palukula (West Estonia). The aim of these networks was a detailed study of local crustal movements in the regions where tectonic faults are located. Repeated levellings as well as gravimetric, electrometric and magnetometric observations were made on those networks. On Viru-Nigula network the measurements of baseline lengths for the determination of horizontal movements were performed. Measurements on the networks were stopped at the end of 1980s due to the lack of financial resources. Repeated high precision gravity measurements on Poltsamaa-Lelle geodynamic line are still carried out nowadays.

Sea-Level Change and Flood Risks at Estonian Coastal Zone

This paper reviews Estonian relative sea level, land uplift and coastal floods data and provides sea-level scenarios and risk assessment of coastal flooding in urban areas for the twenty-first century. Considering the present post-glacial land uplift rates of Estonian coastal areas and the global ocean level rise projections, the long-existing trend of relative sea-level lowering may very probably be replaced by a relative sea-level rising trend during the twenty-first century. By the end of the twenty-first century we project the relative sea level to be c. 20 to 40 cm or c. 40 to 60 cm higher in the case of the International Panel for Climate Change Representative Concentration Pathways (RCP) 4.5 or RCP 8.5 scenario, respectively. The sea-level rise together with the increased storm frequency and decreased winter ice cover period will very probably increase the extent of floods during the twenty-first century. A significant coastal flooding risk affects four cities, Parnu, Kuressaare, Haapsalu and Tallinn and eight smaller towns. The largest coastal flooding in Estonia is recorded in Parnu, with the highest sea level 275 cm in 2005. Calculations show that due to the impact of predicted climate change and in the case of certain weather conditions, coastal floods in Parnu may affect areas up to 400 cm above the present sea level by the end of the twenty-first century. The scenarious of future flood limits are needed for sustainable planning of the coastal zone and for development of rescue strategies.There are already several land use and urban planning instruments and laws for climate adaptation, such as environmental impact assessment, risk assessment and restriction zones for construction in certain buffer and flood areas. Flooding risk measures consist of risk mapping and a national emergency plan. However, further integration of climate issues into existing laws, strategies and land use plans is essential to have a targeted approach in reducing the vulnerability of populated areas and strengthening the adaptive capacity of the urban system against climate change.

Correcting tide gauge series due to land uplift and differences between national height systems of the baltic sea countries

Different types of tide gauges (TG) are used to monitor sea level dynamics around the Baltic Sea. They are usually connected to national levelling network and several of them are linked into regional networks (e.g. Baltic Operational Oceanographic System). The sea level readings are used for nautical navigation, modelling and forecasting of sea level changes. Long-term and historical sea level series are also useful in studying regional land uplift/subsidence or calibrating satellite altimetry data. Both tasks require precise knowledge of interconnections between height systems of countries surrounding the same sea. Presently, however, six different height reference systems are in official use in the Baltic Sea countries. Even though all these systems are based on mean sea level (MSL) observations averaged over different time-periods, but different reference TG and tidal systems have been adopted for national height systems. The differences of national height systems between the countries around the Baltic Sea can reach up to 20 cm. Overlooking this yields undesirable systematic biases between regional TG data. Additionally, the entire Fennoscandia is affected by apparent land uplift at the velocity rate up to +9 mm/year, primarily due to the viscoelastic response of the solid Earth resulting from the de-glaciation of the Pleistocene ice-sheets. Over a time span this causes notable distortions of height system realisations even within a country. Therefore, the land uplift corrections should be also taken into account in sea level series, which are used for modelling and forecasting of sea level changes. A case study in West-Estonian Archipelago involves a recently developed land uplift model EST2013LU, which is based on four repeated high-precision levelling data from 1933 to 2010. Also connections between levelling network and TG series are analysed. The results reveal that discrepancies due to obsoleteness of the heights in the national height system may cause discrepancies in series of nearby located tide gauges up to 7 cm.