Raghuvanshi et al. (2025) Complex network reveals propagation and moisture dynamics of Indian monsoon precipitation extremes

Identification

• Journal: Climate Dynamics
• Year: 2025
• Date: 2025-11-01
• Authors: Akash Singh Raghuvanshi, Ankit Agarwal
• DOI: 10.1007/s00382-025-07924-0

Research Groups

• Department of Hydrology, Indian Institute of Technology, Roorkee, India

Short Summary

This study applies a complex network framework with nonlinear synchronization metrics to analyze the spatiotemporal organization, propagation, and drivers of extreme precipitation events (EPEs) during the Indian Summer Monsoon. It reveals distinct spatial communities influenced by synoptic systems and orography, identifying vertically integrated moisture convergence as the dominant driver of widespread EPEs, with the east coast and Bay of Bengal as major moisture sources and central and western India as primary sink zones.

Objective

• To investigate the spatial and temporal synchronization patterns of EPEs across India by analyzing their propagation dynamics and organizational structure.
• To identify regions acting as moisture sources (EPE propagators) and sinks (EPE receivers), and quantify inter-community interactions through synchronized EPE propagation.
• To characterize the synoptic and monsoon systems responsible for widespread EPEs in different communities across India.
• To examine the role of moisture budget components and moisture transport associated with widespread EPEs across identified communities.

Study Configuration

• Spatial Scale: Indian mainland, gridded at 0.25° × 0.25° resolution.
• Temporal Scale: Indian Summer Monsoon (June–September) for the period 1951–2024. ERA5 data at hourly resolution, aggregated to daily means.

Methodology and Data

• Models used: Complex network framework, Event Synchronization (ES) method with a maximum permissible time delay of 3 days, Random WalkTrap algorithm for hierarchical clustering to delineate communities.
• Data sources:
  • Daily gridded rainfall data from the India Meteorological Department (IMD) at 0.25° × 0.25° resolution.
  • Daily rainfall data from the APHRODITE dataset at 0.25° × 0.25° resolution.
  • ERA5 reanalysis data (hourly, 0.25° × 0.25° resolution) for atmospheric and moisture budget variables: geopotential height at 500 hPa (Z500), specific humidity at 700 hPa (q700), wind fields at 850 hPa and 700 hPa, vertically integrated moisture divergence (VIMD), integrated water vapor (IWV), and surface evaporation (E).

Main Results

• High spatial connectivity and long-range synchronization (Mean Synchronized Distance > 200 km) were observed in the core monsoon region (CMR), west coast (WC), and western Himalayas (WH), linked to monsoonal low-pressure systems (LPSs), low-level jets (LLJs), mid-tropospheric cyclones (MTCs), and orographic features.
• Directed network analysis identified the east coast and Bay of Bengal as major moisture source regions (high negative Network Divergence), while central and western India served as primary moisture sink zones (high positive Network Divergence) for widespread EPEs.
• High betweenness centrality values highlighted important moisture pathways, particularly across the eastern parts of the CMR, the WC adjacent to the Western Ghats, and parts of northeast India.
• Eleven distinct communities of synchronized EPEs were identified, with lead–lag correlation analysis revealing both simultaneous occurrences (e.g., Community 1 and 10) and delayed propagation patterns (e.g., Community 5 leading Community 1 by 4-6 days).
• Composite synoptic diagnostics showed region-specific circulation regimes:
  • Communities 1 and 10 (WH, North India): Rossby wave train patterns, interaction of monsoonal LPS with mid-latitude troughs.
  • Communities 2, 4, 9 (Northeast India, Himalayan foothills): Anomalous anticyclonic circulation over central India/northern Bay of Bengal, northward shift of monsoon trough (break phase).
  • Communities 3, 11 (Southeast India): Westward-propagating anticyclonic circulation over central India/northern Bay of Bengal, double-cell structure (break phase).
  • Communities 5, 8 (Central/Western India): Twin cyclonic circulations (LPS from Bay of Bengal, MTC over Arabian Sea).
  • Community 7 (Western India): Intensifying Arabian Sea MTC with anticyclonic anomalies over northern Bay of Bengal.
  • Community 6 (Western Ghats): Westward-moving LPS from Bay of Bengal, enhanced LLJs.
• Moisture budget analysis confirmed that vertically integrated moisture convergence (VIMC) is the primary driver of widespread EPEs, closely following precipitation anomalies in timing and magnitude, while surface evaporation contributes minimally. Integrated vapor transport (IVT) anomalies generally evolve in phase with precipitation, supporting EPEs.

Contributions

• Provides a comprehensive framework using complex network analysis to understand the spatial and temporal dynamics of EPEs during the Indian Summer Monsoon.
• Identifies specific moisture source and sink regions and their propagation pathways across India, addressing a significant gap in understanding.
• Characterizes the influence of large-scale synoptic systems, intraseasonal variability, and tropical-extratropical interactions on EPE synchronization and clustering at community scales.
• Quantifies the contributions of individual moisture budget components, highlighting the dominant role of vertically integrated moisture convergence.
• Offers valuable insights for improved forecasting, risk assessment, and climate adaptation strategies in the context of changing monsoon dynamics.

Funding

• Prime Minister Research Fellowship (ID- 2803578) from the Ministry of Human Resource Development (MHRD), Government of India.
• Anusandhan National Research Foundation (CRG/2023/ 003449).

Citation

@article{Raghuvanshi2025Complex,
  author = {Raghuvanshi, Akash Singh and Agarwal, Ankit},
  title = {Complex network reveals propagation and moisture dynamics of Indian monsoon precipitation extremes},
  journal = {Climate Dynamics},
  year = {2025},
  doi = {10.1007/s00382-025-07924-0},
  url = {https://doi.org/10.1007/s00382-025-07924-0}
}