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<p>Precipitation is a highly variable climate element, characterized by both systematic and irregular fluctuations, as well as visible and hidden cycles. Due to its inherent and changeable nature, precipitation is influenced by various factors, including large-scale climatic drivers, which add to its complexity. Additionally, precipitation in northwestern Iran has shown significant variability, reflecting the unique characteristics and internal influencing factors of the region.</p><p>Therefore, this study identifies precipitation cycles in northwestern Iran (NWI) from 1970 to 2019 and examines their relationship with Mediterranean atmospheric systems using the Mediterranean Oscillation Index (MOIac), as Iran’s precipitation, particularly in the northwest, is largely influenced by this index, which serves as a key supplier of moisture. To this end, both linear (Pearson correlation) and nonlinear (cross-wavelet analysis) methods were employed. The results reveal dominant fluctuations of 9–15&#xa0;months during the neutral MOIac phase, 5–8&#xa0;months during the positive phase, and 5–9&#xa0;months during the negative phase of MOIac. This shows that both intra-annual and annual cycles are the main fluctuations in the northwest region. Such variations in precipitation are consistent with the seasonal patterns of rainfall in this area of the country. An inverse relationship was observed between precipitation and both the neutral and positive MOIac phases, while a direct relationship was found during the negative phase. Additionally, wavelet-based covariance analysis revealed that the southwestern region of NWI exhibited the highest covariance power, suggesting a strong influence from large-scale atmospheric systems, whereas the eastern half showed the lowest, indicating a greater role of local factors. This pattern is fully consistent with the precipitation conditions in Northwest Iran. Moreover, it indicates that large-scale climatic factors play a greater role in the southwestern part of the region, while their influence diminishes toward the east.</p>

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Identification of precipitation cycles in Northwest Iran (NWI) and their association with the Mediterranean Oscillation Index (MOIac)

  • 期刊论文

  • 发表日期：

    2025年11月9日

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  • Atoosa Khojasteh,
  • Hossein Asakereh,
  • Hassan Shadman

摘要

Precipitation is a highly variable climate element, characterized by both systematic and irregular fluctuations, as well as visible and hidden cycles. Due to its inherent and changeable nature, precipitation is influenced by various factors, including large-scale climatic drivers, which add to its complexity. Additionally, precipitation in northwestern Iran has shown significant variability, reflecting the unique characteristics and internal influencing factors of the region.

Therefore, this study identifies precipitation cycles in northwestern Iran (NWI) from 1970 to 2019 and examines their relationship with Mediterranean atmospheric systems using the Mediterranean Oscillation Index (MOIac), as Iran’s precipitation, particularly in the northwest, is largely influenced by this index, which serves as a key supplier of moisture. To this end, both linear (Pearson correlation) and nonlinear (cross-wavelet analysis) methods were employed. The results reveal dominant fluctuations of 9–15 months during the neutral MOIac phase, 5–8 months during the positive phase, and 5–9 months during the negative phase of MOIac. This shows that both intra-annual and annual cycles are the main fluctuations in the northwest region. Such variations in precipitation are consistent with the seasonal patterns of rainfall in this area of the country. An inverse relationship was observed between precipitation and both the neutral and positive MOIac phases, while a direct relationship was found during the negative phase. Additionally, wavelet-based covariance analysis revealed that the southwestern region of NWI exhibited the highest covariance power, suggesting a strong influence from large-scale atmospheric systems, whereas the eastern half showed the lowest, indicating a greater role of local factors. This pattern is fully consistent with the precipitation conditions in Northwest Iran. Moreover, it indicates that large-scale climatic factors play a greater role in the southwestern part of the region, while their influence diminishes toward the east.