Klaho et al. (2026) Spatiotemporal analysis of lower tail precipitation events over the Eastern Middle East using the complex network to capture drought patterns

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-01-09
• Authors: Mohamad Haytham Klaho, Mohammadali Alijanian, Hamed Yazdian, Somayeh Abedian
• DOI: 10.1016/j.ejrh.2026.103105

Research Groups

• Department of Civil Engineering, Faculty of Civil Engineering and Transportation, University of Isfahan, Isfahan, Iran
• Department of Water Engineering, Faculty of Civil Engineering, University of Aleppo, Aleppo, Syria

Short Summary

This study investigates the spatiotemporal dynamics of lower tail precipitation events (LTPEs) and drought patterns in the Eastern Middle East, focusing on Iran, using a complex network framework. It identifies specific regions like Saudi Arabia, southeastern Iran, Pakistan, and Turkmenistan as severe drought clusters, hubs for propagation, or critical pathways, revealing complex synchronization and directional spread of drought.

Objective

• To comprehend the synchronization structure of lower tail precipitation events (LTPEs) over the Eastern Middle East.
• To establish the direction of spread of LTPEs and drought.
• To determine areas primarily acting as LTPEs spreaders (drought sources) and LTPEs receivers (drought sinks) based on LTPEs analysis to reveal drought conditions.

Study Configuration

• Spatial Scale: Iran and surrounding countries (Eastern Middle East), covering a geographical longitude range of 43.75°E to 63.75°E and latitude range of 25.25°N to 40.75°N, with a spatial resolution of 0.5° × 0.5°.
• Temporal Scale: 30 years (1994–2023) of monthly precipitation data, derived from daily observations.

Methodology and Data

• Models used: Complex Network (CN) framework, Event Synchronization (ES) approach. Undirected and directed complex networks were established, and analyzed using network coefficients including Degree Centrality (DC), Betweenness Centrality (BC), Clustering Coefficient (CC), Mean Synchronized Distance (MSD), Network Divergence (ND), Inward Direction (IDj), and Outward Direction (ODj). The 10th percentile criterion was used to identify LTPEs.
• Data sources:
  • Monthly precipitation data from the Climate Prediction Center (CPC) Global Unified Gauge-Based Analysis (1994–2023).
  • Surface air temperature (2-meter height) from the ERA5 dataset (used for climatology).
  • Meteorological variables (850-hPa geopotential height, zonal and meridional wind components) from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) dataset (used for climatology).
  • All data were regridded to a uniform spatial resolution of 0.5° × 0.5°.

Main Results

• Undirected network analysis (DC, BC, CC) revealed that Saudi Arabia, southeastern Iran, and Pakistan suffer from severe drought, forming localized drought clusters and acting as primary drought hubs.
• The Mean Synchronized Distance (MSD) indicated that eastern, central, and western Iran are significantly impacted by localized droughts, while Saudi Arabia, southeastern Iran, and Pakistan show increased MSD values, implying a heightened risk of extensive drought propagation.
• Directed network analysis (ND, ID, OD) identified Saudi Arabia and Turkmenistan as critical pathways and sources for drought propagation.
• Western and far northwestern Iran, along with parts of eastern Iraq, exhibited positive network divergence, indicating they act as drought sinks.
• Northern, central (Dusht-e Kavir), southeastern regions of Iran, southwestern Turkmenistan, and Pakistan showed negative divergence, signaling them as drought sources.
• Directional orientation evaluations revealed predominant northeast-to-central, southwestern-to-central, and southwestern-to-northwestern trajectories of drought distribution, consistent with regional circulation patterns like mid-latitude westerlies and southeastern monsoons.

Contributions

• Provides a novel approach to drought monitoring by directly analyzing Lower Tail Precipitation Events (LTPEs) using a complex network framework, rather than relying solely on standard drought indices or trend tests.
• Offers new hydrological insights into the synchronization, distribution, and directional spread of drought in the Eastern Middle East, a particularly vulnerable region.
• Introduces the concept of Mean Synchronized Distance (MSD) as an innovative metric for geophysical applications, integrating geographic length and synchronization magnitude.
• Delivers actionable insights for regional drought monitoring and management, enabling identification of vulnerable basins and prioritization of mitigation strategies.

Funding

• Iran Water Resources Management Company

Citation

@article{Klaho2026Spatiotemporal,
  author = {Klaho, Mohamad Haytham and Alijanian, Mohammadali and Yazdian, Hamed and Abedian, Somayeh},
  title = {Spatiotemporal analysis of lower tail precipitation events over the Eastern Middle East using the complex network to capture drought patterns},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103105},
  url = {https://doi.org/10.1016/j.ejrh.2026.103105}
}