Moghim et al. (2025) Complete assessment of the heat waves and cold waves in different regions

Identification

• Journal: Natural Hazards
• Year: 2025
• Date: 2025-09-10
• Authors: Sanaz Moghim, Soroush Bayat
• DOI: 10.1007/s11069-025-07600-w

Research Groups

• Department of Civil Engineering, Sharif University of Technology, Tehran, Iran

Short Summary

This study comprehensively assesses heat waves and cold waves in six global cities using various definitions, indicators, and climate scenarios for historical (1990–2000) and future (2030–2040) periods. It develops a novel Extreme Wave Index (EWI) to compare regional vulnerability, revealing an increasing trend in heat wave severity and a decreasing trend in cold wave severity, with significant regional variations.

Objective

• To assess heat waves and cold spells in different regions using various definitions and indicators.
• To compare the characteristics of heat waves and cold spells in several regions across historical and future periods under different climate scenarios.
• To develop a new vulnerability index (Extreme Wave Index, EWI) to quantify relative vulnerability and exposure to heat waves and cold spells.

Study Configuration

• Spatial Scale: Six large cities: Tehran, London, Madrid, New York, Shanghai, and Vancouver. Data extracted from corresponding 1.125° × 1.125° grid cells.
• Temporal Scale:
  • Baseline period: 1970–1980
  • Historical period: 1990–2000
  • Projection period: 2030–2040
  • Climate scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5

Methodology and Data

• Models used: MRI-ESM2-0 from CMIP6.
• Data sources: Daily maximum, average, and minimum temperature data; daily relative humidity and wind speed data, all obtained from the MRI-ESM2-0 model.

Main Results

• Heat Waves (HWs):
  • Most HW features (frequency, average temperature, intensity, duration) are projected to show an upward trend in all case studies for 2030–2040 under all climate scenarios.
  • Tehran, London, and Madrid are expected to face higher risks from heat waves based on the Extreme Wave Index (EWI).
  • Dynamic thresholds generally lead to a higher frequency of HW occurrences compared to static thresholds.
  • Compound HWs in Tehran are projected to increase significantly in frequency (55% to 75% relative to baseline), duration (approximately double), and total days (more than double), with over 90% of future HWs being compound events.
• Cold Waves (CWs):
  • Most CW features are projected to show a downward trend in all cities for 2030–2040, except for Vancouver under SSP2-4.5.
  • Vancouver and Tehran are projected to be more vulnerable to cold wave threats based on the EWI.
  • Dynamic thresholds generally result in a lower frequency of CW occurrences compared to static thresholds.
  • Compound CWs in Tehran are projected to decrease in frequency (more than 50% decrease) and total days (35% to 45% decrease).
• Extreme Wave Index (EWI):
  • The developed EWI shows an increasing trend in vulnerability to HWs across all cities, with Tehran, London, and Madrid exhibiting the highest risk depending on the scenario.
  • Vulnerability to CWs is projected to decrease in most cities, with Vancouver and Tehran remaining more vulnerable.
• Definition Importance: The severity of HW/CW features varies significantly based on different indicators (e.g., Effective Temperature (ET), Apparent Temperature (AT), Heat Index (HI), Humidex) and thresholds (static/dynamic), emphasizing the need for context-specific definitions. For instance, ET is found to be improper for determining HWs but suitable for extreme CWs.

Contributions

• Provides a comprehensive assessment of both heat waves and cold waves using a diverse set of definitions, indicators (including thermal comfort indices), and thresholds (static and dynamic).
• Compares HW and CW characteristics across six geographically diverse global cities for historical and future periods under three Shared Socioeconomic Pathway (SSP) climate scenarios.
• Introduces a novel Extreme Wave Index (EWI) that integrates event frequency and intensity to offer a relative measure of vulnerability/exposure, facilitating cross-regional and cross-temporal comparisons.
• Analyzes compound heat and cold waves, highlighting the projected increase in severity for future heat events.
• Offers a valuable framework for developing sustainable adaptation and mitigation plans and alarming systems across various sectors globally.
• This is identified as the first study to assess and compare extreme heat waves and particularly cold waves using different thresholds and indicators in various locations.

Funding

• This research was supported by Sharif University of Technology (SUT) through Grant QB020103. No specific grant from other funding agencies was received.

Citation

@article{Moghim2025Complete,
  author = {Moghim, Sanaz and Bayat, Soroush},
  title = {Complete assessment of the heat waves and cold waves in different regions},
  journal = {Natural Hazards},
  year = {2025},
  doi = {10.1007/s11069-025-07600-w},
  url = {https://doi.org/10.1007/s11069-025-07600-w}
}