Irrigation Sciences and Engineering

Irrigation Sciences and Engineering

Joint Frequency Analysis of Meteorological Drought Duration and Severity Based on ERA5-Land Reanalysis Database

Document Type : Research Paper

Authors
Ameneh Mianabadi 1
Mohammad Nazeri Tahroudi 2
Mohsen Pourreza-Bilondi 3
1 Department of Ecology, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.
2 Department of Water Engineering, Faculty of Agriculture, Lorestan University, Khorramabad. Iran.
3 Department of Water Engineering, Faculty of Agriculture, University of Birjand, Birjand. Iran.
10.22055/jise.2025.48618.2150
Abstract
Drought is a natural phenomenon that occurs when precipitation is below normal levels over period of time and is characterized by duration, severity, intensity, and frequency. Due to climate change, these characteristics have changed, necessitating updated monitoring methods. Drought characteristics were often examined separately through univariate - analyses; however, drought is an interrelated, multivariate phenomenon whose attributes are dependent on one another. Therefore, recent studies have recommended joint analysis of drought characteristics using multivariate probability functions. This study used copula functions to analyze drought duration and severity jointly. Daily precipitation data from Bandar Anzali (wet, 1755 mm average annual rainfall) and Kerman (dry, 131 mm average annual rainfall) were analyzed from 1959 to 2020 using ERA5-Land reanalysis. The Standardized Precipitation Index (SPI) was calculated for six time scales (1, 3, 6, 9, 12, and 24 months). After fitting marginal distribution functions to the variables and confirming the correlation between drought duration and severity, the best copula functions were selected for each timescale. The results showed that in the "AND" condition (D≥d AND S≥s), the probability of similar droughts was higher in Kerman than in Bandar Anzali, while in the "OR" condition (D≥d OR S≥s), the probability of droughts with either high duration or severity was greater in Bandar Anzali. Furthermore, estimating return periods by considering both duration and severity jointly provided a more accurate assessment of drought events. The resulting curves, which demonstrate the relationship between drought duration, severity, and return period, can serve as standard references for the Bandar Anzali and Kerman stations across various time scales. These curves remain applicable as long as the statistical distribution of drought duration and severity does not change. They provide a practical tool for monitoring drought across different time windows and devising more effective strategies for water resource management and mitigating drought impacts.
Keywords
Copula Function
Drought Duration
Drought Severity
Marginal Distribution
Reanalysis
SPI
Subjects
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Irrigation Sciences and Engineering
Volume 49, Issue 1
Spring 2026
Pages 59-84

  • Receive Date 26 December 2024
  • Revise Date 21 April 2025
  • Accept Date 12 May 2025
  • Publish Date 05 May 2026