Global spatiotemporal patterns of heatwaves: a re-evaluation.

Area of Science:

• Climate Science
• Extreme Weather Events
• Environmental Monitoring

Background:

• Heatwaves are significant climate extremes whose analysis is sensitive to baseline climate definitions.
• Methodological choices, especially baseline selection, influence the detection and quantification of heatwave characteristics like frequency, duration, and intensity.

Purpose of the Study:

• To evaluate the impact of baseline selection on global heatwave characterization using ERA5-Land data from 1981-2023.
• To compare a fixed historical baseline with a running 30-year climatology baseline.
• To introduce and assess a ratio-based intensity metric normalized by local variability.

Main Methods:

• Global analysis of atmospheric heatwaves utilizing ERA5-Land reanalysis data (1981-2023).
• Comparison of heatwave trends derived from a fixed baseline (1951-1980) versus a running baseline.
• Application of a novel ratio-based intensity metric to normalize temperature anomalies by local variability.

Main Results:

• Baseline choice significantly influences the apparent magnitude and trends of heatwave frequency, duration, and intensity.
• A running baseline attenuates trends by accounting for long-term warming, revealing deviations from evolving conditions.
• Normalized intensity metrics reduce the pronounced latitudinal gradient seen with absolute anomalies, suggesting more even relative thermal exposure.

Conclusions:

• Methodological transparency in baseline selection is crucial for accurate heatwave assessment and risk evaluation.
• Running baselines and variability-normalized metrics offer essential complementary perspectives for analyzing extremes in a non-stationary climate.
• Findings underscore the need for careful consideration of analytical methods when comparing heatwave studies and assessing impacts.