Citation: Walanus, A.; Twardosz, R.; Cebulska, M.; Plachta, A. In Search of Periodicity in the Annual Precipitation in Europe (1881–2020). Water 2022, 14, 2026. https://doi.org/10.3390/ w14132026 Academic Editor: Scott Curtis Received: 23 May 2022 Accepted: 22 June 2022 Published: 24 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article In Search of Periodicity in the Annual Precipitation in Europe (1881–2020) Adam Walanus 1 , Robert Twardosz 2, * , Marta Cebulska 3 and Arkadiusz Plachta 2 1 Geophysics and Environmental Protection, Faculty of Geology, AGHUniversity of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland; walanus@agh.edu.pl 2 Faculty of Geography and Geology, Jagiellonian University, ul. Gronostajowa 7, 30-387 Kraków, Poland; arekplachta6@gmail.com 3 Faculty of Environmental and Power Engineering, Cracow University of Technology, ul. Warszawska 24, 31-155 Kraków, Poland; marta.cebulska@pk.edu.pl * Correspondence: r.twardosz@uj.edu.pl Abstract: A new method of searching for periodicity has been developed on the basis of extensive spatio-temporal data. The result, however, produces little more than doubts. The standard Fourier analysis indicates some periods, namely 3.7-, 7.0-, 8.8-, and 17.5-year periods, and these periodic signals are distributed relatively consistently over some regions of Europe. However, the expectations that the exact harmonic 8.8 years of 17.5 years, and not so exact 3.7 years of 7.0 years will be present at the same or close stations are not fulfilled. Keywords: annual precipitation totals; periodic variability; Fourier transform; Europe 1. Introduction As the climate grows warmer [1,2], huge numbers of publications on air temperature changes are being released. The greatest warming of the climate has been observed in Europe [3], and the scenarios of change imply that the warming is bound to intensify [4]. Recent research has shown that average temperatures have been rising to varying degrees from one part of Europe to another [5]. Overall, the warming intensifies towards the northeast of the continent [6]. An increase in the variability of precipitation has been observed in recent decades, which have been exceptionally warm. For example, 2010 was a year of heavy precipitation and disastrous floods in central Europe [7], and 2018 saw a long period of hot and dry weather in many areas of the continent [8–10]. Obviously, there are a number of determinants behind precipitation. In addition to temperature and content of water vapour in the atmosphere, geographical factors also play a role. This multitude of factors of precipitation complicates attempts to establish a link between changes in precipitation and warming [11–13]. This is also mirrored by projections of precipitation amounts modelled on the basis of various scenarios [4]. Long-term precipitation trends are characterised by fluctuations, that is, alternating periods with excess and shortfall of precipitation [14,15]. Naturally, this raises the question whether these fluctuations can have the nature of cyclical changes. In other words, can they be described by statistical methods (by a statistical model)? The search for an answer to such a question is an important issue from the point of view of the forward-looking management of water resources in a given area. Recent decades have seen a noticeable acceleration of the hydrological processes involved in the water cycle in nature as a result of a growing frequency of extreme weather phenomena. To solve water-related problems successfully, the cyclical behaviour of the components of the water cycle needs to be understood [16]. Of course, the issue of cyclicity addressed in this paper is not new, as it dates back to the 19th century [17]. The present research into the cyclicity of precipitation across Europe was inspired by a statistically significant 35-year Brückner cycle of annual precipitation, Water 2022, 14, 2026. https://doi.org/10.3390/w14132026 https://www.mdpi.com/journal/water