In this study, researchers introduce the initial phase of developing an impact-based forecasting system for extreme heatwaves, utilizing a novel multivariate index. This index combines a statistical approach with physical principles related to human body water loss and includes a mitigation plan focused on hydration measures.

Since 1990, heatwaves have become increasingly frequent and intense worldwide, particularly in Europe and Asia. The primary health impacts of these heatwaves include organ strain, exacerbation of cardiovascular and kidney diseases, and adverse reproductive effects, especially in individuals aged 65 and older.

While many national meteorological services have established metrics to assess the frequency and severity of heatwaves, most rely on specific threshold values of near-surface air temperature, often derived from historical records. Few metrics consider the persistence of heatwave events or account for relative humidity.

This study aims to develop a globally applicable normalized index suitable for various temporal scales and regions. The index incorporates health risks associated with relative humidity, accounts for the duration of extreme heatwave events, and is sensitive to exposure above critical temperature thresholds.

The research computed the index under two scenarios: forecasting heatwave episodes using the WRF model and evaluating its relationship with mortality data and maximum temperature anomalies during the 2003 summer heatwave in Spain. Additionally, the study assessed the annual trend of increasing extreme heatwaves in Spain using ERA5 climate data.

Results indicate that this index has considerable potential as a decision-support and health risk assessment tool, demonstrating greater sensitivity to extreme risk episodes compared to traditional evaluations of extreme temperatures. Its formulation aligns with the physical mechanisms of water loss in the human body and factors in the effects of relative humidity.