Abstract Drought is controlled and enhanced by changes in the local and global climate factors. The changes in the global factors mainly occur on the vast oceanic surfaces, while the changes in the local factors occur in the area of drought influence. In order to skilfully forecast and monitor drought occurrences, it is crucial that the specific causal factors be identified and their links studied. Based on this concept, this study tried to establish a relationship between the drought occurrences in Tigray region and the climate factors at the local and global scale. Monthly gridded Climatic Research Unit (CRU) Time-series (TS) data version 4.01 was used to calculate the Standardized Precipitation and Evapotranspiration Index (SPEI). As potential global causal factors, SOI (Southern Oscillation Index), Sea Surface Temperature Anomalies (SSTAs) of the tropical oceanic surfaces, the Red Sea and Nino 3.4 regions were obtained from various sources. Vegetation cover and albedo data were also considered as local drought causal factors. The analyses results show that the zero-time-lag SSTA in the tropical Indian Ocean was identified as statistically significant (p < 0.01) drought influencing factor accounting for 5.8% and 8% of the variations in SPEI, at 1-month and 6-month time scales respectively. At 12-month time scale, however, the SSTAs in the tropical Indian Ocean, tropical Atlantic Ocean, tropical Pacific Ocean, the Red Sea and Nino 3.4 regions were designated as drought influencing factors. Differently, at 24-month time scale, SOI was also identified as drought influencing factor in addition to the SSTAs in the tropical Indian Ocean, tropical Pacific Ocean and the Red Sea region. In general, the findings revealed the variability in the number and type of causal factors based on time scale and time-lag. Nevertheless, the ability of the identified factors to explain the variation in SPEI remained small at all timescales investigated. This, therefore, indicates the need for further investigation on other drought causal factors in the study area.

中文翻译：

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埃塞俄比亚北部提格雷地区干旱发生及其成因关系分析

摘要 干旱受局地和全球气候因素变化的控制和加剧。全球因素的变化主要发生在广阔的海洋表面，而局地因素的变化发生在干旱影响区。为了巧妙地预测和监测干旱的发生，确定具体的因果因素并研究它们之间的联系是至关重要的。基于这一概念，本研究试图建立提格雷地区干旱发生与局部和全球尺度气候因素之间的关系。每月网格气候研究单位 (CRU) 时间序列 (TS) 数据版本 4.01 用于计算标准化降水和蒸散指数 (SPEI)。作为潜在的全球因果因素，SOI（南方涛动指数），热带海洋表面、红海和 Nino 3.4 区域的海面温度异常 (SSTA) 是从各种来源获得的。植被覆盖和反照率数据也被认为是当地干旱的原因。分析结果表明，热带印度洋零时滞 SSTA 被确定为具有统计学意义（p < 0.01）的干旱影响因素，分别占 SPEI 变化的 5.8% 和 8%，在 1-个月和 6-分别为月时间尺度。然而，在 12 个月的时间尺度上，热带印度洋、热带大西洋、热带太平洋、红海和 Nino 3.4 地区的 SSTA 被指定为干旱影响因素。不同的是，在 24 个月的时间尺度上，除热带印度洋的 SSTA 外，SOI 也被确定为干旱影响因素，热带太平洋和红海地区。总的来说，研究结果揭示了基于时间尺度和时滞的因果因素的数量和类型的可变性。然而，在所有调查的时间尺度上，所确定的因素解释 SPEI 变化的能力仍然很小。因此，这表明需要进一步调查研究区的其他干旱成因。