Nivar

Nivar

Application of Spectral Analysis for Determination of Daily Rainfall Frequency in the Urmia Lake Basin

Articles in Press

Document Type : Original Article

Authors
Shima Kabiri 1
Mohammadali Nasresfahani 2
Ahmadreza Ghasemi Dastgerdi 3
1 PhD student, Department of Water Engineering, Faculty of Agriculture, Shahrekord University
2 Assistant Professor, Department of Water Engineering, Faculty of Agriculture, Shahrekord University
3 Associate Professor, Department of Water Engineering, Faculty of Agriculture, Shahrekord University
10.30467/nivar.2026.530926.1341
Abstract
Understanding long-term precipitation behavior, as one of the most variable climatic elements, plays a crucial role in water resource management and in reducing the vulnerability of agricultural and natural resource sectors. Since temporal and spatial variations in precipitation can lead to wide-ranging economic, social, and environmental consequences, the application of modern approaches such as spectral analysis to identify rainfall patterns and cycles is essential. In this study, spectral analysis was employed to investigate the dominant frequencies of daily precipitation within the Lake Urmia basin. Daily data from 11 selected meteorological stations across the basin, covering a minimum 20-year statistical period (1970–2022), were analyzed. Furthermore, three representative stations—Tabriz, Kahriz, and Mahabad—located at different positions around Lake Urmia, were examined in greater detail to assess precipitation behavior under normal, drought, and wet conditions. The research methodology was based on spectral analysis using the Fourier series, applied to daily precipitation data from the 11 stations with at least 20 years of records. After data collection from the Meteorological Organization, quality control procedures were carried out, and wet and dry years were identified using the Standardized Precipitation Index (SPI). The results revealed that annual and semi-annual cycles play a primary role in the temporal distribution of rainfall across most stations; however, their intensity and persistence vary depending on geographical location. Under normal conditions, stations exhibit relatively regular and concentrated precipitation patterns. During drought periods, cycles become weakened and more scattered, whereas in wet years, stronger long-term cycles emerge, leading to more coherent precipitation behavior. Return period analysis indicated that drought tends to recur annually in most of the 11 stations, while wet conditions display more diverse temporal patterns, sometimes appearing over short multi-day intervals. This variability in temporal distribution, particularly in stations with shorter cycles, reflects a more unstable climate and greater sensitivity to climatic fluctuations. The findings highlight the importance of tailoring water resource management strategies to the specific frequency characteristics of each region and demonstrate that spectral analysis can serve as a valuable decision-support tool for drought mitigation and optimizing water storage planning.
Keywords
Spectral Analysis
Urmia Lake
Draught
Wet Spell
Rainfall
Subjects
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Nivar

Articles in Press, Accepted Manuscript
Available Online from 09 February 2026

  • Receive Date 22 June 2025
  • Revise Date 05 January 2026
  • Accept Date 09 February 2026
  • Publish Date 09 February 2026