Drought is recognized as a natural hazard and environmental disaster, and has caused extensive impact worldwide. The increasing frequency and severity of droughts associated with global climate change is an important issue in agriculture and water resources. Given the critical situation of water resources in the Lake Urmia Basin, predicting drought characteristics in future periods is very important in this basin. In this study, to evaluate the future drought and wet spells in Lake Urmia Basin, the daily outputs of the second-generation Canadian Earth System Model (CanESM2) model under RCP2.6, RCP4.5 and RCP8.5 emission scenarios were projected and downscaled using the Statistical Downscaling Model (SDSM) model for two periods, 2031–2050 and 2051–2070. Subsequently, the drought status and its trends in the baseline period (1986–2005) and future periods were investigated using precipitation data and the Standardized Precipitation Index (SPI). Then, the drought and wet spell characteristics including occurrence, persistence and the stationary probability of each class were calculated using the Markov chain model. The results showed that the probability of droughts in the stations of Lake Urmia Basin increased in the future. Also, by increasing SPI timescales, drought persistence increased under all three scenarios. On the other hand, by increasing the SPI timescales, the intensity of droughts and wet spells decreased, while their persistence increased.

中文翻译：

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评估气候变化对乌尔米亚湖流域干旱和潮湿的影响

干旱被认为是一种自然灾害和环境灾难，并在世界范围内造成了广泛的影响。与全球气候变化相关的干旱频率和严重程度的增加是农业和水资源领域的一个重要问题。鉴于乌尔米亚湖流域水资源的严峻形势，预测该流域未来时期的干旱特征非常重要。在这项研究中，为了评估乌尔米亚湖盆地未来的干旱和湿润期，在 RCP2.6、RCP4.5 和 RCP8.5 排放情景下，第二代加拿大地球系统模型 (CanESM2) 模型的日产量被预测和使用统计缩减模型 (SDSM) 模型缩减了两个时期，2031-2050 和 2051-2070。随后，使用降水数据和标准化降水指数 (SPI) 研究了基线期（1986-2005 年）和未来时期的干旱状况及其趋势。然后，利用马尔可夫链模型计算各类干旱和湿润期的发生、持续时间和平稳概率等特征。结果表明，未来乌尔米亚湖流域站台发生干旱的概率增加。此外，通过增加 SPI 时间尺度，所有三种情景下的干旱持续性都增加了。另一方面，通过增加 SPI 时间尺度，干旱和湿润期的强度降低，而其持续性增加。使用马尔可夫链模型计算各类干旱和湿润期特征，包括发生、持续和平稳概率。结果表明，未来乌尔米亚湖流域站台发生干旱的概率增加。此外，通过增加 SPI 时间尺度，所有三种情景下的干旱持续性都增加了。另一方面，通过增加 SPI 时间尺度，干旱和湿润期的强度降低，而其持续性增加。使用马尔可夫链模型计算各类干旱和湿润期特征，包括发生、持续和平稳概率。结果表明，未来乌尔米亚湖流域站台发生干旱的概率增加。此外，通过增加 SPI 时间尺度，所有三种情景下的干旱持续性都增加了。另一方面，通过增加 SPI 时间尺度，干旱和湿润期的强度降低，而其持续性增加。