Dey et al. (2025) Assessment of extreme climate trends using temperature, rainfall, and cyclones in the West Bengal coastal region

Identification

• Journal: Scientific Reports
• Year: 2025
• Date: 2025-10-06
• Authors: Mousumi Dey, Vinod Kumar Bhardwaj
• DOI: 10.1038/s41598-025-99705-2

Research Groups

• Dr. Harisingh Gour Vishwavidyalaya, (A Central University), Sagar, M.P., India.
• DST-FIST-sponsored GIS Lab, Department of General and Applied Geography, Dr. Harisingh Gour Vishyavidyalaya.
• GSITI, Hyderabad.
• Department of Geography, Ramananda Centenary College, Purulia.

Short Summary

This study analyzed 42 years (1982–2023) of rainfall, temperature, and extreme climate events in the West Bengal coastal region, revealing statistically significant increasing trends in annual and post-monsoon rainfall (surpassing monsoon levels), rising minimum temperatures, and an increasing frequency of cyclonic events, which collectively heighten flood risk and impact agricultural planning.

Objective

• To conduct a combined analysis of the trend, frequency, and magnitude of seasonal and annual rainfall, temperature, and cyclones in the West Bengal coastal region.
• To identify change points within the rainfall and temperature time series data using the Sequential Mann–Kendall (SQMK) test.
• To calculate and analyze trends for 21 extreme climate indices to understand historical weather patterns and their implications for coastal climate change.

Study Configuration

• Spatial Scale: Four weather stations (Digha, Contai, Diamond Harbour, Sagar Island) in the West Bengal coastal region, covering East Mednipur and South 24 Parganas districts, with an approximate coast length of 210 km.
• Temporal Scale: Daily time series data for 42 years (1982–2023) for rainfall and temperature. Cyclonic activity data from 1982–2023 for the West Bengal coast and 1951–2023 for the Bay of Bengal.

Methodology and Data

• Models used:
  • Mann–Kendall test
  • Sen’s slope estimator method
  • Coefficient of variation
  • Sequential Mann–Kendall (SQMK) test
  • Innovative Trend Analysis (ITA)
  • RClimdex platform (for 21 ETCCDMI extreme climate indices)
• Data sources:
  • Gridded (0.25°×0.25°) daily rainfall, maximum and minimum temperature data (1982–2023) from the Centre for Hydrometeorology and Remote Sensing (CHRS) website.
  • Cyclonic activity data from the Indian Meteorological Department (IMD) Cyclone e-Atlas.
  • Population data from Census of India 2001 and 2011.

Main Results

• Temperature Trends:
  • Statistically significant decreasing trend in maximum temperature at Contai and Diamond Harbour.
  • Increasing trend in maximum temperature at Digha and Sagar Island.
  • Statistically significant rising trends in minimum temperatures across all stations.
  • A notable downward trend in TN10P (cool nights) across all stations, with magnitudes ranging from -0.17 °C/year to -0.31 °C/year.
  • A significant decreasing trend in TN90P (warm nights) across all stations, with magnitudes ranging from -0.2 °C/year to -0.32 °C/year.
  • Statistically significant increasing trend in TNx (monthly maximum daily minimum temperature) at Diamond Harbour.
• Rainfall Trends:
  • Statistically significant upward trends in annual, pre-monsoon, monsoon, and post-monsoon rainfall across all monitoring stations.
  • Post-monsoonal rainfall increases with greater magnitude at all stations, exceeding monsoon rainfall levels and indicating a shifting rainfall pattern.
  • Statistically significant increasing trend in Consecutive Wet Days (CWD) at all stations, with magnitudes ranging from 0.5 days/year to 0.89 days/year.
  • Significant increases in R10mm, R20mm, R95p (very wet days), and R99p (extreme wet days) for the examined stations. The highest R95p magnitude was 11.13 mm/year at Sagar, and the highest R99p magnitude was 5.27 mm/year at Digha.
  • Significant positive trends in Simple Precipitation Intensity Index (SDII), RX1day (maximum 1-day precipitation, 0.93 to 1.25 mm/year), and RX5days (maximum 5-day precipitation, 1.23 to 2.48 mm/year) were observed.
• Change Points:
  • Multiple statistically significant change points were detected in annual rainfall across all stations, with a common change year of 1995.
  • No significant change points were found for maximum temperature, and only one for annual minimum temperature at Sagar station (1995).
• Cyclonic Events:
  • An increasing trend in the annual frequency of depressions, cyclonic storms, and super cyclonic storms making landfall along the West Bengal coast (1982–2023).
  • A similar upward trend in the frequency of super cyclonic storms (SCS) in the Bay of Bengal (1951–2023).
• Impacts: Alterations in rainfall patterns negatively impact the environment and economy, increasing the likelihood of post-monsoon flooding, adversely affecting agricultural output, and raising food security concerns. Increased RX1 days and RX5 days may lead to storm surges and extreme coastal floods.

Contributions

• Provides a comprehensive, combined analysis of trends, frequency, and magnitude for seasonal and annual rainfall, temperature, and cyclones in the West Bengal coastal region.
• Utilizes the Sequential Mann–Kendall test to identify significant change points in climatic variables, offering insights into shifts in weather patterns.
• Calculates and analyzes trends for 21 extreme climate indices, addressing a notable research gap in understanding coastal climate change and its extreme events in this specific vulnerable region.
• Enhances the understanding of coastal climate change dynamics, which is crucial for developing informed adaptation strategies for local populations, agricultural planning, and water resource management.

Funding

• DST-FIST (Department of Science & Technology - Fund for Improvement of S&T Infrastructure) for providing GIS Lab facilities at Dr. Harisingh Gour Vishyavidyalaya.

Citation

@article{Dey2025Assessment,
  author = {Dey, Mousumi and Bhardwaj, Vinod Kumar},
  title = {Assessment of extreme climate trends using temperature, rainfall, and cyclones in the West Bengal coastal region},
  journal = {Scientific Reports},
  year = {2025},
  doi = {10.1038/s41598-025-99705-2},
  url = {https://doi.org/10.1038/s41598-025-99705-2}
}