Rakshit et al. (2025) Unprecedented winter precipitation over Delhi NCR, India (December 2024): a multi-Sensor perspective

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2025
• Date: 2025-11-24
• Authors: Gargi Rakshit, Kaustav Chakravarty, Ashis Mitra, Ram Kumar Giri
• DOI: 10.1007/s00704-025-05898-x

Research Groups

• India Meteorological Department, Ministry of Earth Sciences, Government of India, New Delhi, India
• Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune, India

Short Summary

This study comprehensively analyzes an unprecedented intense winter precipitation event over Delhi NCR on 27 December 2024 using multi-sensor observations and reanalysis, revealing it was driven by a synergy of synoptic forcing, mesoscale convergence, and dual-source moisture advection.

Objective

• Quantify the microphysical characteristics of rainfall using ground-based disdrometer data, focusing on raindrop size distribution parameters and rainfall intensity.
• Analyze key atmospheric parameters associated with the event using INSAT-3DR and ERA5 reanalysis data, with a focus on Cloud Top Brightness Temperatures (CTBT), Outgoing Longwave Radiation (OLR), divergence and convergence fields, water vapor winds, and the driving forces behind vertically integrated moisture transport.
• Characterize lightning activity associated with the convective outbreak using data from the IITM Lightning Location Network.
• Elucidate the origin and transport pathways of atmospheric moisture, with particular emphasis on the role of sustained moisture advection from the Arabian Sea and Bay of Bengal, as inferred from ERA5-based Vertically Integrated Moisture Transport (VIMT) diagnostics and HYSPLIT back trajectory model analysis.

Study Configuration

• Spatial Scale: Delhi National Capital Region (NCR), Northwest India, Central Asia, Pakistan, Afghanistan, Arabian Sea, Bay of Bengal, northern Chhattisgarh.
• Temporal Scale: Event: 27 December 2024. Contextual data: December 2022, 2023, 2024 (disdrometer); 1991–2020 (climatological mean for rainfall); 1981–2023 (climatological mean for VIMT); 5-day backward trajectories.

Methodology and Data

• Models used: HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model, ERA5 reanalysis (European Centre for Medium-Range Weather Forecasts - ECMWF).
• Data sources: Ground-based Joss–Waldvogel Disdrometer (JWD, Distromet RD-80), S-band Doppler Weather Radar (DWR) at Palam, New Delhi, INSAT-3DR satellite products (Thermal Infrared (TIR1) channel for Cloud Top Brightness Temperatures (CTBT), Outgoing Longwave Radiation (OLR), upper-level divergence, lower-tropospheric convergence, water vapor wind), IITM (Indian Institute of Tropical Meteorology) Lightning Location Network (LLN) by Earth Networks.

Main Results

• Delhi NCR experienced an unprecedented winter precipitation event on 27 December 2024, recording the highest single-day December rainfall in recent decades (e.g., North East Delhi: 60.1 mm).
• Disdrometer data showed nearly 15 hours of intermittent rainfall with peaks exceeding 40 mm/h, characterized by a prevalence of larger raindrops (> 3 mm diameter) during intense periods, indicative of strong convective updrafts and efficient coalescence.
• Doppler Weather Radar captured deep convective towers exceeding 10 km in height, transitioning to stratiform rain with a bright band near 4–5 km altitude.
• Satellite observations (INSAT-3DR) confirmed deep convection with CTBT below 225 K and OLR values under 180 W m⁻², associated with widespread and intense lightning activity (anomaly of 0.10 to 0.28 flash km⁻² day⁻¹).
• ERA5 reanalysis and HYSPLIT model revealed robust vertically integrated moisture transport (VIMT) from both the Arabian Sea and the Bay of Bengal, showing a pronounced positive anomaly on 27 December 2024.
• The event was driven by a dynamic interaction between an eastward-propagating upper-level trough (Western Disturbance) and persistent low-level easterlies from an anticyclonic circulation over central India, creating a convergence corridor over northwest India.
• This interaction resulted in strong low-level convergence (+10 × 10⁻⁵ s⁻¹) and upper-level divergence (≥ 10–20 × 10⁻⁵ s⁻¹), sustaining deep convective updrafts.

Contributions

• Provides the first integrated analysis combining microphysical and dynamical diagnostics to elucidate the multiscale drivers of a rare winter convective event over Delhi NCR.
• Advances understanding of Indian winter precipitation and its urban convective manifestations through synergistic use of ground-based sensors, satellite remote sensing, model outputs, and reanalysis products.
• Offers critical insights for urban meteorology, flood-risk modeling, lightning hazard assessment, and impact-based early warning systems in the context of changing climate.

Funding

• The authors acknowledge the India Meteorological Department (IMD) and the Director General of Meteorology (DGM) for providing facilities.
• The Director, IITM, Pune, is acknowledged for encouragement.

Citation

@article{Rakshit2025Unprecedented,
  author = {Rakshit, Gargi and Chakravarty, Kaustav and Mitra, Ashis and Giri, Ram Kumar},
  title = {Unprecedented winter precipitation over Delhi NCR, India (December 2024): a multi-Sensor perspective},
  journal = {Theoretical and Applied Climatology},
  year = {2025},
  doi = {10.1007/s00704-025-05898-x},
  url = {https://doi.org/10.1007/s00704-025-05898-x}
}