The purpose of this study is to analyze the spatiotemporal variations in drought in Serbia over recent decades using the standardized precipitation evapotranspiration index (SPEI). The analysis is performed for time series of 1-, 3-, 6-, and 12-month SPEI indices (SPEI-01, SPEI-03, SPEI-06 and SPEI-12, respectively) calculated using the -OBS gridded dataset with a horizontal resolution of 0.1° for the period of 1950–2022. In general, it was found that negative SPEI trends prevailed in Serbia for all months and all analyzed SPEI timescales, indicating a more frequent appearance of droughts in recent decades. Moreover, for a large majority of month-timescale combinations, the area with a negative trend was larger than the area with a positive trend. For several reasons, we focused on the SPEI for August. First, the SPEI for this month shows one of the most pronounced negative trends, which is rather consistent over different timescales and consistent in terms of the area over which the trend was found to be significant. Statistically significant negative trends of SPEI-03, −06 and − 12 for August were found over 11, 17 and 38% of the country area, respectively. To better understand the trends and changes in the SPEI for August, focusing on extreme and severe drought events, an innovative trend analysis (ITA) was applied. It was found that the occurrence of both extreme and severe SPEI drought categories has doubled over the last thirty years in comparison with the previous thirty-year period. Additionally, more frequent transitions from neutral and wet categories to dry categories were observed through an application of the Markov chain. Second, the special focus on SPEI-03, −06 and − 12 for August was motivated by the fact that we found a significant correlation between these index values and the annual maize production in Serbia, indicating that the SPEI for August can be useful for the assessment of drought impact on agriculture. To better understand interannual variability and long-term trends, this paper also explores the relations between the SPEI over Serbia and large-scale circulation patterns, together with general global and continental warming trends. Our findings indicate that drought changes over recent decades may be driven by the interplay of long-term warming and large-scale circulation patterns. In the context of climate change, especially climate projections, Serbia is situated in a region for which climate projections of mean precipitation change demonstrate weak signals and often with conflicting signs of change within multimodel ensembles. From this point of view, our results can be seen as a contribution to a better understanding of changes in extremes, in our case droughts, that can be hidden by inconclusive changes in the mean values. Finally, due to the similar situation in terms of precipitation and drought trends and changes, our results may be relevant for a wider region, and not only for Serbia.

中文翻译：

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利用高分辨率网格数据分析塞尔维亚干旱近期趋势和时空变化

本研究的目的是利用标准化降水蒸散指数（SPEI）分析塞尔维亚近几十年来干旱的时空变化。对使用 -OBS 网格数据集计算的 1、3、6 和 12 个月 SPEI 指数（分别为 SPEI-01、SPEI-03、SPEI-06 和 SPEI-12）的时间序列进行分析1950年至2022年期间的水平分辨率为0.1°。总体而言，发现塞尔维亚所有月份和所有分析的 SPEI 时间尺度都普遍存在 SPEI 负趋势，这表明近几十年来干旱出现得更加频繁。此外，对于绝大多数月时间尺度组合，负趋势区域大于正趋势区域。出于多种原因，我们重点关注 8 月份的 SPEI。首先，本月的 SPEI 显示出最明显的负面趋势之一，该趋势在不同时间尺度上相当一致，并且在发现趋势显着的区域方面也一致。 8 月份 SPEI-03、-06 和 -12 的统计显着负趋势分别在超过 11%、17% 和 38% 的国家地区出现。为了更好地了解8月份SPEI的趋势和变化，重点关注极端和严重干旱事件，应用了创新趋势分析（ITA）。研究发现，与前三十年相比，过去三十年极端和严重 SPEI 干旱类别的发生次数增加了一倍。此外，通过马尔可夫链的应用，观察到从中性和潮湿类别到干燥类别的更频繁的转变。其次，特别关注 8 月的 SPEI-03、-06 和 -12 是因为我们发现这些指数值与塞尔维亚玉米年产量之间存在显着相关性，这表明 8 月的 SPEI 可用于评估干旱对农业的影响。为了更好地了解年际变化和长期趋势，本文还探讨了塞尔维亚上空的 SPEI 与大尺度环流模式之间的关系，以及全球和大陆变暖的总体趋势。我们的研究结果表明，近几十年来的干旱变化可能是由长期变暖和大规模环流模式的相互作用驱动的。在气候变化，特别是气候预测的背景下，塞尔维亚所处的地区平均降水量变化的气候预测显示出微弱的信号，并且多模式集合中的变化迹象往往相互矛盾。从这个角度来看，我们的结果可以被视为对更好地理解极端变化的贡献，在我们的例子中是干旱，这种变化可能被平均值的不确定变化所隐藏。最后，由于降水和干旱趋势和变化方面的情况相似，我们的结果可能适用于更广泛的地区，而不仅仅是塞尔维亚。