Shukla et al. (2026) Atmospheric drivers of the 26 May 2025 heavy rainfall event over mumbai: insights from observations and reanalysis

Identification

• Journal: Natural Hazards
• Year: 2026
• Date: 2026-04-13
• Authors: Krishna Kumar Shukla, Anoop Kumar Mishra, Gajendra Kumar, Dipak Kumar Sahu, Shubhangi Bhute, Sourav Adhikary
• DOI: 10.1007/s11069-026-08118-5

Research Groups

• Central Aviation Meteorological Division, India Meteorological Department, Ministry of Earth Sciences, New Delhi, India
• India Meteorological Department, Ministry of Earth Sciences, Mumbai, India

Short Summary

This study investigates the atmospheric drivers of a very heavy rainfall event (0.18 m in 24 hours) over Mumbai on 26 May 2025, combining observations and reanalysis data. It reveals that the event was caused by a synergistic interaction of early monsoon onset, abundant moisture influx from the Arabian Sea, strong coastal moisture convergence, high atmospheric instability, and the dominance of low-base deep convective clouds.

Objective

• To investigate the atmospheric and oceanic conditions that triggered a very heavy rainfall event over Mumbai, emphasizing moisture transport, convergence mechanisms, and convective cloud development, given the earliest monsoon onset in 75 years.
• To understand the dominance of cloud base height during this very heavy rainfall event.

Study Configuration

• Spatial Scale: Mumbai coast, Indian subcontinent. Data analyzed at 0.25° × 0.25° spatial resolution for gridded rainfall and reanalysis. Ceilometer and radiosonde data specific to Mumbai.
• Temporal Scale: 23–27 May 2025 for rainfall and ceilometer data; 23–26 May 2025 for gridded rainfall, reanalysis, and radiosonde data. Rainfall observations every 30 minutes; ERA5 data at 1-hour resolution; radiosonde data at 0000 and 1200 UTC.

Methodology and Data

• Models used: ERA5 reanalysis (ECMWF fifth-generation global reanalysis).
• Data sources:
  • In-situ rain gauge records from automated weather stations in Mumbai.
  • India Meteorological Department (IMD) regridded rainfall datasets (0.25° × 0.25°).
  • Automated Weather Observing Systems (AWOS) Ceilometer (Vaisala CL31) data from Mumbai airport for cloud base height (CBH).
  • Radiosonde data from the University of Wyoming (WMO station code: 43003, Mumbai) for atmospheric instability indices (Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), K index (KI), Totals Totals Index (TOTL), Lifted Index (LI), Severe Weather Evaluation And Threat (SWEAT) index).

Main Results

• Mumbai experienced a very heavy rainfall event on 26 May 2025, with a cumulative rainfall exceeding 0.18 m in 24 hours.
• Ceilometer observations showed that all three cloud base heights (CBH1, CBH2, CBH3) persisted below 1.8 km during the event, with the day mean CBH1 decreasing to 327 m on 26 May 2025, indicating the dominance of deep convective clouds.
• ERA5 reanalysis successfully captured the spatial distribution of heavy rainfall, consistent with IMD's gridded rainfall.
• ERA5 precipitable water vapour (PWV) showed a marked increase near Mumbai on 26 May 2025, approaching ~0.016 m, indicating enhanced atmospheric moisture availability.
• Radiosonde-derived CAPE showed a significant enhancement to 3045 J/kg at 12 UTC on 25 May 2025, indicating a highly unstable environment prior to the event. Other instability indices also showed corresponding increases, while CIN decreased.
• Vertically Integrated Moisture Divergence (VIMD) analysis revealed a pronounced moisture convergence cell near the Mumbai coast from 23 May 2025, which intensified subsequently.
• Vertically Integrated Moisture Transport (VIMT) analysis highlighted strong low-level southwesterly fluxes from the Arabian Sea, transporting moisture-laden air towards the west coast of India, peaking over the Arabian Sea basin during 23–25 May 2025 and extending zonally on 26 May 2025.
• The event was driven by the synergistic interaction of abundant low-level moisture supply from the Arabian Sea, strong coastal convergence, high atmospheric instability, and the presence of low-base deep convective clouds, coupled with an early monsoon onset.

Contributions

• Provides a comprehensive analysis of the atmospheric drivers of a specific very heavy rainfall event over Mumbai, linking early monsoon onset with local convective conditions.
• Demonstrates the first scientific application of Automated Weather Observing Systems (AWOS) Ceilometer (CL31) observations in India for hazard assessment, highlighting the value of the 'Mission Mausam' AWOS network for aviation meteorology and urban flood preparedness.
• Emphasizes the synergistic role of multiple atmospheric processes (moisture supply, convergence, instability, cloud structure) in extreme precipitation events.
• Underscores the importance of integrated multi-parameter monitoring for improving early warning systems for urban flood preparedness and aviation hazard management in coastal megacities.

Funding

None. The study acknowledges the Ministry of Earth Sciences, New Delhi, India, for providing the automated weather observing system (AWOS) at Mumbai under ‘Mission Mausam’.

Citation

@article{Shukla2026Atmospheric,
  author = {Shukla, Krishna Kumar and Mishra, Anoop Kumar and Kumar, Gajendra and Sahu, Dipak Kumar and Bhute, Shubhangi and Adhikary, Sourav},
  title = {Atmospheric drivers of the 26 May 2025 heavy rainfall event over mumbai: insights from observations and reanalysis},
  journal = {Natural Hazards},
  year = {2026},
  doi = {10.1007/s11069-026-08118-5},
  url = {https://doi.org/10.1007/s11069-026-08118-5}
}