Identifying the Dynamics of the Sea-Level Fluctuations in Croatia Using the RAPS Method
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S S symmetry Article Identifying the Dynamics of the Sea-Level Fluctuations in Croatia Using the RAPS Method Danko Markovinovi´c 1, Nikola Kranjˇci´c 2,* , Bojan Ðurin 1 and Olga Bjelotomi´cOršuli´c 3 1 Department of Civil Engineering, University North, Jurja Križani´ca31b, 42000 Varaždin, Croatia; [email protected] (D.M.); [email protected] (B.Ð.) 2 Faculty of Geotechnical Engineering, University of Zagreb, Hallerova aleja 7, 42000 Varaždin, Croatia 3 IGEA Ltd., Frana Supila 7/b, 42000 Varaždin, Croatia; [email protected] * Correspondence: [email protected] Abstract: Seawater level changes are affected by natural and anthropogenic impacts. While climate changes are considered to be a cause for all significant recent variations in meteorological and hydrological parameters, there is still a need for the analysis at the smaller regional scale, especially of the seawater level changes. A regional analysis is essential for early warning of upcoming changes that could, firstly, affect islands and coastal areas and, subsequently, expand on larger areas. The determined regional changes could affect the salinity of drinking water sources, increase the presence of natural flooding, and impact land degradation. In this paper, an analysis of local seawater level fluctuations is provided for three available locations in Croatia distributed along the Adriatic Sea’s coast. The rescaled adjusted partial sums (RAPS) method was used and applied on time series of the average daily seawater levels for each location. Visual interpretation of the RAPS method indicated the appearance of common regularities of the observed quantities, in this case, averaged daily seawater level changes. Also, it was shown that the regional shape and indentation of the coast Citation: Markovinovi´c,D.; Kranjˇci´c, did not have a strong effect on the seawater level’s rise. Seasonal changes in the sea level are mostly N.; Ðurin, B.; Bjelotomi´cOršuli´c,O. periodic and, therefore, have symmetry visible in its behavior. Fluctuations in the dynamics of sea Identifying the Dynamics of the level studied in this paper were not regular and predictable with simple linear equations, but the Sea-Level Fluctuations in Croatia symmetry was also found to be present in the irregularities identified with the RAPS method. Using the RAPS Method. Symmetry 2021, 13, 289. https://doi.org/ Keywords: sea level; climate impact; regularities; climate changes; RAPS; Adriatic Sea 10.3390/sym13020289 Academic Editor: Francisco G. Montoya 1. Introduction Received: 3 January 2021 Generally, relative sea-level changes are caused by transfers of water mass between oceans Accepted: 4 February 2021 Published: 8 February 2021 and continents due to the enlargement and deflation of immense ice layers. These changes are mainly caused by global climate changes. However, significant vertical movements in Publisher’s Note: MDPI stays neutral the Earth’s crust appear over long periods of time that should also be taken into the account. with regard to jurisdictional claims in These movements cannot be exactly determined and their value stated, but they can be published maps and institutional affil- identified and eliminated to some extent from Earth observations. This includes co-seismic iations. uplift and subsidence during hazardous earthquakes (Mw > 8), Earth’s surface displacements caused by a long-term process of glacial isostatic adjustment, and global ocean volume changes as a result of plate–tectonic movements [1]. Not only are vertical changes affected by the mentioned Earth processes, but sea-level changes also reshape coastal surroundings by their horizontal shift. The main impacts of sea-level rise are increased coastal erosion and loss of the Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. land, increased risk of flooding, and saltwater intrusion into freshwater resources [2]. This article is an open access article The abovementioned processes occur at different locations on Earth. There is no single distributed under the terms and location at which all of these processes are happening at the same time. Therefore, it is conditions of the Creative Commons impossible to record them collectively at once. However, we can record and monitor the Attribution (CC BY) license (https:// behavior of one of the processes, observing its behavior, and analyze any possible regular creativecommons.org/licenses/by/ trends that can be identified as a systematic and periodic Earth behavior resulting in a 4.0/). clearer set of original measurements. Symmetry 2021, 13, 289. https://doi.org/10.3390/sym13020289 https://www.mdpi.com/journal/symmetry Symmetry 2021, 13, x FOR PEER REVIEW 2 of 14 Symmetry 2021, 13, 289 2 of 14 regular trends that can be identified as a systematic and periodic Earth behavior resulting in a clearer set of original measurements. The rate of sea-levelsea-level rise has increased. Between the years 1900 and 1990,1990, studies showshow that that the the s seaea level rose between 1.2 mm and 1.7 mm per year on average at a global levellevel as as measured by satellite altimetry [3]. [3]. By By the the year year 2000, 2000, that that rate had increased to approximately 3.2 mm per year, and the rate in 2016 was estimated to be 3.4 mm per year. approximately 3.2 mm per year, and the rate in 2016 was estimated to be 3.4 mm per year. In 2019, the sea level rose 3.3 mm. Figure1 shows the rise in sea level over the last three In 2019, the sea level rose 3.3 mm. Figure 1 shows the rise in sea level over the last three decades at a global level. As mentioned in Reference [4], during the period 1993–2018, decades at a global level. As mentioned in Reference [4], during the period 1993–2018, the the sea level varied from −1.41 + −0.47 mm per year for six locations in the Adriatic Sea sea level varied from −1.41 + −0.47 mm per year for six locations in the Adriatic Sea FigureFigure 1. 1. RiseRise in in the the sea sea level level at at a a global global level from from 1993 1993 to to 2019 2019 [ 3[3]]. Numerous studiesstudies havehave dealt dealt with with the the estimation estimation of how of how much much and howand fasthow the fast global the globalaverage average sea level sea is level rising. is Therising. main The difference main difference among the among studies the is studies the analytical is the analytical approach. approach.The first approach The first quantitatively approach quantitatively describes the describes physical the processes physical contributing processes contributing to the global tosea the rise global [2], such sea rise as thermal [2], such change as thermal influence change on influence ocean water on ocean volume, water land volume, ice melting, land iceand melting, changing and the changing depth of globalthe depth ocean of basinsglobal [ocean5], while basins the second[5], while approach the sec triesond approach to predict trtheies future to predict rise inthe sea future levels rise based in sea on level observeds based temperature on observed changes. temperature The first changes. approach The firstwas approach used in Intergovernmental was used in Intergovernmental Panel on Climate Panel Change on Climate (IPCC) Change climate (IPCC) assessments. climate assessments.Within this approach, Within this physical approach, models physical are used models to estimate are used contributions to estima fromte contributions the sea level fromcomponents, the sea level such components as thermal expansion, such as thermal and melting expansion from glaciers and melting and the from dynamics glaciers of and ice thesheets, dynamics with their of ice summation sheets, with in their the last summation stage of estimation in the last [stage6–8]. of The estimation second approach [6–8]. The is secondbased on approach a hypothesis is based that on the a sea hypothesis level rises that faster the as sea it gets level warmer rises faster [2]. This as it approach gets warmer uses [2].semiempirical This approach models uses insemiempirical order to form models statistical in order relationships to form statistical between relationships sea-level change be- tweenand global sea-level temperature change and [9–11 global] or radiative temperature forcing [9– [11]12, 13or], radiative respectively. forcing [12,13], respec- tively.Sea-level fluctuations, which occur over wide ranging timescales, may have periodic or aperiodicSea-level characteristics fluctuations, which visible. occur Symmetry over wide can beranging detected timescale in irregularitiess, may have in periodic rescaled oradjusted aperiodic partial character sumsistics (RAPS) visible. graphs, Symmetry since the can dynamics be detected of sea in level irregularities studied in in this rescaled paper adjustedare not predictable partial sums with (RAPS linear) graphs, trendlines. since The the mostdynamics recognizable of sea level periodic studied oscillations in this paper are the ones that occur due to the fact of seasonal changes in density or meteorological param- are not predictable with linear trendlines. The most recognizable periodic oscillations are eters [14]. Aperiodic sea-level changes cannot be assigned to an exact cause, since their the ones that occur due to the fact of seasonal changes in density or meteorological pa- behavior does not reoccur in the same shape at the same time intervals. They are the rameters [14]. Aperiodic sea-level changes cannot be assigned to an exact cause, since their result of several meteorological dynamic processes that cannot be determined separately behavior does not reoccur in the same shape at the same time intervals. They are the result and eliminated from observations. In addition, anthropogenic influences [14] were re- of several meteorological dynamic processes that cannot be determined separately and cently acknowledged and recognized as significant factors regarding sea-level changes, eliminated from observations. In addition, anthropogenic influences [14] were recently comprising greenhouse gases and increases in the temperature of Earth’s atmosphere, acknowledged and recognized as significant factors regarding sea-level changes, compris- which consequently also induce a rise in sea levels.