Abstract Meteorological droughts due to the concurrent occurrence of low-precipitation and high-temperature events can lead to severe negative impacts on agriculture, economy, ecosystem, and society. This study proposes a novel framework to characterize such drought conditions based on the joint variability of precipitation–temperature, particularly under climate change. Generalized hierarchical linear model is used to downscale precipitation and temperature at multiple stations from the outputs of nine General Circulation Models (GCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. A bivariate drought index called Precipitation–Temperature Deciles Index (PTDI) is developed using copulas to assess changes in future dry/hot conditions. The methodology is applied to the Lake Urmia basin located in a semi-arid region in the northwest of Iran. Lake Urmia, the sixth largest salt lake in the world at the original size, has shrunk dramatically causing environmental and socioeconomic disruptions. Results suggest that the climate of the region is projected to shift toward drier/hotter conditions in the future. The multi-model ensemble means of all GCMs shows an increase of ~4 °C in the regional temperature and ~25 mm (8%) decrease in precipitation in 2060–2080 based on RCP8.5. The magnitude of climate-induced water deficit is projected to increase under all future scenarios. According to the PTDI, projected changes in the number of “extremely dry/hot” months in 2060–2080 under RCP4.5 and RCP8.5 relative to the historical period vary between 2.4 and 7.3% and 4.5–13.2%, respectively. This condition is unfavorable for the revival of the endangered lake while maintaining the agricultural activities in the region.

中文翻译：

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气候变化下乌尔米亚湖流域气象干旱风险增加：引入降水-温度十分位数指数

摘要 低降水和高温事件同时发生造成的气象干旱会对农业、经济、生态系统和社会造成严重的负面影响。这项研究提出了一个新的框架，根据降水-温度的联合变异性来表征这种干旱条件，特别是在气候变化下。广义分层线性模型用于根据代表性浓度路径 (RCP) 4.5 和 8.5 下的九个一般环流模型 (GCM) 的输出对多个站点的降水和温度进行降尺度。一种称为降水-温度十分位指数 (PTDI) 的双变量干旱指数是使用 copula 开发的，以评估未来干燥/炎热条件的变化。该方法应用于位于伊朗西北部半干旱地区的乌尔米亚湖盆地。乌尔米亚湖是世界上第六大盐湖，以原始大小计算，已经急剧缩小，造成环境和社会经济破坏。结果表明，该地区的气候预计未来将转向更干燥/更热的条件。所有 GCM 的多模式集合均值显示，基于 RCP8.5，2060-2080 年区域温度升高约 4 °C，降水减少约 25 毫米（8%）。在所有未来情景下，气候引起的缺水量预计都会增加。根据 PTDI，RCP4.5 和 RCP8.5 下 2060-2080 年“极端干燥/炎热”月份的数量相对于历史时期的预测变化分别在 2.4-7.3% 和 4.5-13.2% 之间变化。