Assessment of groundwater determinative recharge seasons and their spatial distribution in the Baltic States based on response to historical drought 1989–2018

<p>To assess groundwater response to climate change scenarios in the context of groundwater drought it is fundamental to understand controlling periods of groundwater recharge as well response time to meteorological forcing (Hughes et al 2021, Jasechko et al 2014).&#160;</p><p>The study aims at assessing the spatial and temporal distribution of groundwater drought events in the Baltic States over the period 1989 &#8211; 2018 as well as the meteorological and hydrological indicators associated with periods of below-normal groundwater level. A set of meteorological, hydrological and groundwater drought indices were used for the identification of significant drought events in the region. Used groundwater level time series were treated and checked for errors according to the Retike et al. (2021).</p><p>Four major drought events affecting all monitoring sites under study are identified (1992&#8211;1994, 1996&#8211;1997, 2002&#8211;2004 and 2005&#8211;2007), although, the fluctuations in groundwater level display distinct patterns which might be associated with the impact of local meteorological conditions and geological setting of particular monitoring sites such as seasonally derived recharge. It was found that meteorological drought indices (SPI, SPEI, DRI) showed the highest correlation with groundwater drought conditions rather than hydrological indices (SRI and SSRI) calculated from ERA-5 reanalysis data. FHowever, for most indices and most monitoring sites there is a one month time lag between the signal of the hydrometeorological index and the response of groundwater drought. Time series analysis of drought indices at groundwater monitoring sites demonstrated varying characteristics of the onset, duration, and propagation of drought events through different scales thus highlighting the complex nature of groundwater drought events in the Baltic State area.</p><p>This research is funded by the Latvian Council of Science, project &#8220;Spatial and temporal prediction of groundwater drought with mixed models for multilayer sedimentary basin under climate change&#8221;, project No. lzp-2019/1-0165.</p><p>&#160;</p><p><br><br></p><p>References</p><p>Jasechko, Scott & Birks, Sandra & Gleeson, Tom & Wada, Yoshihide & Fawcett, Peter & Sharp, Zachary & McDonnell, Jeffrey & Welker, Jeff. (2014). The pronounced seasonality of global groundwater recharge. Water Resources Research. 50. 10.1002/2014WR015809.</p><p>Hughes, A. & Mansour, Majdi & Ward, Rob & Kieboom, Natalie & Allen, S. & Seccombe, David & Charlton, Matthew & Prudhomme, C. (2021). The impact of climate change on groundwater recharge: National-scale assessment for the British mainland. Journal of Hydrology. 598. 126336. 10.1016/j.jhydrol.2021.126336.</p><p>Retike, I., Bik&#353;e, J., Kalv&#257;ns, A., D&#275;li&#326;a, A, Avotniece, Z., Zaadnoordijk, W.J., Jemeljanova, M., Popovs,K., Babre, A., Zelenkevi&#269;s, A., Baikovs, A. (2022) Rescue of groundwater level time series: How tovisually &#160; identify &#160; and &#160; treat &#160; errors. &#160; Journal &#160; of &#160; Hydrology, &#160; 605, &#160; 127294.https://doi.org/10.1016/j.jhydrol.2021.127294</p>