Pre-print of Hydrogeology Journal, http://dx.doi.org/10.1007/s10040-017-1665-2 Investigation of the climate-driven periodicity of shallow groundwater level fluctuations in 1 a Central-Eastern European agricultural region 2 3 Tamás Garamhegyi 1 , József Kovács 1 , Rita Pongrácz 2 , Péter Tanos 3 , István Gábor Hatvani 4* 4 5 1. Eötvös Loránd University, Department of Physical and Applied Geology, H-1117 Budapest, 6 Hungary; 7 email: garamhegyit@gmail.com, kevesolt@gmail.com 8 2. Eötvös Loránd University, Department of Meteorology, H-1117 Budapest, Hungary; 9 email: pongracz.rita@gmail.com 10 3. Szent István University, Department of Mathematics and Informatics, H-2100, Gödöllő, 11 Hungary 12 email: tanospeter@gmail.com 13 4. Institute for Geological and Geochemical Research, Research Center for Astronomy and 14 Earth Sciences, MTA, Budaörsi út 45., Budapest, H-1112, Hungary 15 email: hatvaniig@gmail.com 16 *Corresponding author 17 18 Abstract 19 The distribution and amount of groundwater, a crucial source of Earth’s drinking and irrigation 20 water, is changing due to climate-change effects. Therefore, it is important to understand 21 groundwater behavior in extreme scenarios, e.g. drought. Shallow groundwater (SGW) level 22 fluctuation under natural conditions displays periodic behavior, i.e. seasonal variation. Thus, the 23 study aims to investigate (i) the periodic behavior of the SGW level time series of an agriculturally 24 important and drought-sensitive region in Central-Eastern Europe – the Carpathian Basin, in the 25 north-eastern part of the Great Hungarian Plain, and (ii) its relationship to the European 26 atmospheric pressure action centers. Data from 216 SGW wells were studied using wavelet 27 spectrum analysis and wavelet coherence analyses for 1961-2010. Locally, a clear relationship 28 exists between the absence of annual periodic behavior in the SGW level and the periodicity of 29 droughts, as indicated by the self-calibrating Palmer Drought Severity Index and the Aridity Index. 30