In hydrology, precipitation is the most critical variable and plays the most significant role in the hydrological cycle (Yang et al. 2020b). Precipitation is a crucial variable for water resources management and weather-related research. However, due to the negative impacts of climate change on the atmosphere, more intense precipitation and severe droughts have occurred, resulting in changes to the spatial and temporal distribution of precipitation patterns (Kidd and Huffman 2011, Papalexiou and Montanari 2019, Cui et al. 2022). While in some regions, people and the environment experience more severe droughts and water shortages, in others, several floods and heavy precipitation events are occurring more than in the past (Donat et al. 2017, Guo et al. 2020). These abnormalities, including changes in the amount of precipitation, changes in frequency, time shifting, and concentration, have a considerable influence on social life and the ecosystem (Donat et al. 2017, Papalexiou and Montanari 2019). Over earth's land, precipitation has risen by nearly 2% due to global warming, which could raise the water-holding capability of the atmosphere by approximately 7% per one-degree increase in temperature, which could intensify anomalies in the distribution of precipitation (Cui et al. 2022, Darand and Pazhoh 2022). For example, due to mentioned changes, in Iran, semi-arid areas over 400 years have transformed into arid regions (Gholami et al. 2017).
Changes in precipitation patterns and regime could raise concerns about the management of water resources and the feasibility of sustainable development plans. For instance, temperature increases and changes in precipitation patterns can significantly affect evaporation rates and soil moisture conditions during the growing season, as well as water losses in large reservoirs or lakes (Pizarro et al. 2013, Cui et al. 2022, Eini et al. 2023b). In this regard, Guo et al. (2020) investigated how spatiotemporal changes in precipitation concentration affect drought events across China. Their results demonstrate that changes in precipitation patterns have varying effects on drought events in different regions of China. Alternatively, Yang et al. (2020a) have shown that precipitation regime changes are closely related to teleconnection indices over Central Asia. Yang et al. (2020b) have identified that shifts from light to heavy rainfall could cause the risk of heavy floods and soil erosion and lead to substantial water resource management issues. Therefore, studying spatiotemporal changes in precipitation could enhance our comprehension of various adverse effects of climate change on a region.
To detect changes in precipitation concentration patterns, various indices and statistical methods have been proposed and tested in different regions. These include the Precipitation Concentration Index (PCI), Long-cycle Drought-Flood Abrupt Alternation Index (LDFAI), Precipitation Concentration Period (PCP), Multi-time Scale Mutual Information Entropy (MTSMIE), and Precipitation Concentration Degree (PCD) (Martin-Vide 2004, Li et al. 2011, Cortesi et al. 2012, Cui et al. 2022, Darand and Pazhoh 2022). Using these indices over Bangladesh, an abnormal trend in precipitation concentration was detected (Mondol et al. 2018). Over Europe, by employing these indices, it is noted that ocean/sea have primary effects on the spatial distribution of the concentration indices (Cortesi et al. 2012). Darand and Pazhoh (2022) have identified that precipitation concentration is increased, and the frequency of the number of wet days is decreased in Iran. However, according to Cortesi et al. (2012), daily rainfall distribution has not substantially changed over Europe from 1971 to 2010. In addition, these indices help identify the effect of teleconnections indices on droughts and flood events (Yang et al. 2020a, Yin et al. 2021, Xie et al. 2022). However, in most of the studies, researchers have focused on the changes in the amount of precipitation and negative trends in precipitation over the regions, but spatiotemporal precipitation changes in many regions are still unknown (Wibig 2009, Hänsel et al. 2019, Szwed 2019, Blahušiaková et al. 2020, Yang et al. 2020a, Kalbarczyk and Kalbarczyk 2022, Łupikasza and MaŁarzewski 2022).
Based on the literature, Central Europe is one of the regions where several droughts and floods have happened during the past decades and caused several socio-economic issues (Hisdal et al. 2001, Mudelsee et al. 2003, Gvoždíková and Müller 2017, Ionita et al. 2021, Tomczyk et al. 2022). These hazards are mainly linked to changes in precipitation; however, anthropogenic changes could intensify these problems (Kundzewicz et al. 2005, Bryndal 2015, Boergens et al. 2020). In addition, in the north of this region the Baltic Sea is located, and according to its characteristics, the Baltic sea region is sensitive to meteorological droughts as low flows could affect the quality of the Baltic Sea and its ecosystem (Kundzewicz 2009, Meier et al. 2012, Babre et al. 2022, Piniewski et al. 2022, Rutgersson et al. 2022).
The motivation of this study is the lack of analyses on precipitation concentration indices in this region, while several studies have investigated the trends in the study area (Wibig 2009, Hänsel et al. 2019, Szwed 2019, Blahušiaková et al. 2020, Ziernicka-Wojtaszek and Kopcinska 2020, Kalbarczyk and Kalbarczyk 2022). This study is novel in that it represents the first comprehensive evaluation of precipitation concentration variability in a region of Central Europe using various indices, based on a gridded dataset. The study aims to assess precipitation concentration indices, periods of occurrence, and trends using a high-resolution, regional precipitation dataset. The findings of this study could enhance our understanding of the impact of precipitation concentration changes on regional drought monitoring, soil erosion, land conservation, and other related areas.