Development and Application of the Warm Spell Magnitude Index daily (WSMId) in historical European heatwaves

Heatwaves and prolonged periods of extremely high temperatures are increasingly recognized for their significant impact across various regions and societal sectors, such as energy resources management, human health or agriculture. So far, the scientific community has focused on better understanding summer heatwaves with the use of various definitions and climatic indices. In this context, we introduce the Warm Spell Magnitude Index daily (WSMId) for extending beyond the warm period. This index is designed to capture the characteristics of consecutive days with anomalous high temperatures throughout the year, ultimately allowing us to investigate the various drivers behind prolonged periods of extreme heat.

WSMId builds upon the Heat Wave Magnitude Index daily (HWMId) by Russo et al. (2015), adapting a similar mathematical framework to identify heatwave-like events across multiple seasons. Calibration is based on the ERA5 reanalysis, focusing on the most intense summer European heatwaves of the past decades. Through this exercise, we aim in ensuring that the new index can meaningfully quantify episodes of anomalous warmth in non-summer periods, such as “false spring effects,” “extended summer periods,” and clustering of heatwaves.

This work could allow us to explore the underlying drivers behind these phenomena, aiming at enhancing our understanding of regional heatwave dynamics and their broader implications. We envision that WSMId will offer as a valuable tool for climate scientists, with potential applications in seasonal forecasting, development of climate adaptation strategies, and impact studies.

 

References

Russo, S., Sillmann, J., & Fischer, E. M. (2015). Top ten European heatwaves since 1950 and their occurrence in the coming decades. Environmental Research Letters, 10(12), 124003. https://doi.org/10.1088/1748-9326/10/12/124003