Abstract：
Based on the physical and geographical conditions, the Baltic Region is categorised as a humid climate zone. This means that, there is usually more precipitation than evaporation throughout the year, suggesting that droughts should not occur frequently in this region. Despite the humid climate in the region, the study focused on assessing the spatio-temporal patterns of droughts. The drought events were analysed across the Baltic Region, including Sweden, Finland, Lithuania, Latvia, and Estonia. This analysis included two drought indices, the Standardized Precipitation Index (SPI) and the Streamflow Drought Index (SDI), for different accumulation periods. Daily data series of precipitation and river discharge were used. The spatial and temporal analyses of selected drought indices were carried out for the Baltic Region. In addition, the decadal distribution of drought classes was analysed to disclose the temporal changes and spatial extent of drought patterns. The Pearson correlation between SPI and SDI was applied to investigate the relationship between meteorological and hydrological droughts. The analysis showed that stations with more short-duration SPI or SDI cases had fewer long-duration cases and vice versa. The number of SDI cases (SDI ≤ -1) increased in the Western Baltic States and some WGSs in Sweden and Finland from 1991 to 2020 compared to 1961-1990. The SPI showed no such tendencies except in Central Estonia and Southern Finland. The 6-month accumulation period played a crucial role in both the meteorological and hydrological drought analyses, as it revealed prolonged and widespread drought events. Furthermore, the 9- and 12-month accumulation periods showed similar trends in terms of drought duration and spatial extent. The highest number of correlation links between different months was found between SPI12-SDI9 and SPI12-SDI12. The results obtained have deepened our understanding of drought patterns and their potential impacts in the Baltic Region.
摘要：
根据自然和地理条件，波罗的海区域被归类为湿润气候区。这意味着,全年的降水量通常多于蒸发量，这表明该地区不应该经常发生干旱。尽管该地区气候潮湿，这项研究的重点是评估干旱的时空模式。对整个波罗的海区域的干旱事件进行了分析，包括瑞典,芬兰,立陶宛,拉脱维亚,和爱沙尼亚。这项分析包括两个干旱指数，标准降水指数(SPI)和水流干旱指数(SDI)，对于不同的积累期。使用了降水和河流排放的每日数据系列。对波罗的海区域的干旱指数进行了时空分析。此外,分析了干旱类别的年代际分布，以揭示干旱模式的时间变化和空间范围。SPI和SDI之间的Pearson相关性用于研究气象和水文干旱之间的关系。分析表明，短期SPI或SDI病例较多的站的长期病例较少，反之亦然。与1961-1990年相比，1991年至2020年，西波罗的海国家的SDI病例数（SDI≤-1）以及瑞典和芬兰的一些WGS增加。除了在爱沙尼亚中部和芬兰南部，SPI没有显示出这种趋势。6个月的累积期在气象和水文干旱分析中起着至关重要的作用，因为它揭示了长期和广泛的干旱事件。此外，9个月和12个月的累积期在干旱持续时间和空间范围方面显示出相似的趋势。在SPI12-SDI9和SPI12-SDI12之间发现不同月份之间的相关联系数量最高。获得的结果加深了我们对波罗的海区域干旱模式及其潜在影响的理解。
