Abstract Identification of subregions that share similar historical drought variability provides useful information for drought monitoring, mitigation planning, and resource allocation. This study examined space-time historical drought variability for the Great Plains spanning from 1901 to 2015 by using rotated Empirical Orthogonal Functions (rEOFs). The Standardized Precipitation-Evapotranspiration Index (SPEI) on a three-month timescale was utilized to examine spatial and temporal changes in agricultural drought. We propose a new procedure for identifying the number of rEOFs to be selected for reconstructing subregions. Drought event intensities of moderate, severe, and extreme categories increased in recent years although the number of drought events decreased. Seasonal rEOFs demonstrated that 9–12 subregions were adequate to explain a significant proportion of the original variability in the Great Plains. The time series for each subregion was highly correlated to the original SPEI data and reflected the seasonal meteorological processes that drive drought variability. Several significant wetting trends were found, and there was statistical evidence that drought and wetting event severities had increased for a few subregions. Summer drought has become more variable across space and time, indicating that a more diverse set of resources and strategies might be needed to mitigate impacts of spatially-variable drought and wetting events in coming decades. Winter season drought has become less variable, indicating that perhaps resources could be consolidated when dealing with impacts on a larger scale; however, less variability implies that drought and wetting events may occur across larger regions of the Great Plains during a given season.

中文翻译：

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确定美国大平原季节性干旱监测的水文气候子区域

摘要 识别具有相似历史干旱变异性的次区域可为干旱监测、减缓规划和资源分配提供有用的信息。本研究使用旋转经验正交函数 (rEOF) 研究了大平原从 1901 年到 2015 年的时空历史干旱变化。三个月时间尺度上的标准化降水-蒸发蒸腾指数 (SPEI) 用于检查农业干旱的时空变化。我们提出了一种新的程序来确定要选择用于重建子区域的 rEOF 的数量。尽管干旱事件数量有所减少，但近年来中度、重度和极端类别的干旱事件强度有所增加。季节性 rEOF 表明 9-12 个子区域足以解释大平原原始变异的很大一部分。每个子区域的时间序列与原始 SPEI 数据高度相关，反映了驱动干旱变异的季节性气象过程。发现了几个显着的润湿趋势，并且有统计证据表明一些次区域的干旱和润湿事件的严重程度有所增加。夏季干旱在空间和时间上的变化越来越大，这表明可能需要更多样化的资源和策略来减轻未来几十年空间变化的干旱和湿润事件的影响。冬季干旱的变数变小了，这表明在应对更大范围的影响时，或许可以整合资源；