Multidecadal Heatwave Magnitude Variability of Türkiye

Human-induced climate change is rapidly increasing the magnitude and frequency of temperature extremes across the Mediterranean Basin. Türkiye is critically situated within this region due to its distinctive peninsular nature, being bounded by seas on three sides and intersected by complex mountain chains that strongly modulate local climate patterns. Observations indicate a distinct transition in summer temperatures. Between 1970 and 1990, average summer temperatures persisted within the 22–23°C. However, a rapid warming phase beginning in the early 2000s increased the mean summer temperature to the 24–25°C range. This steady warming trend peaked in 2024, when the average summer temperature reached a historical maximum of 26.1°C. Against this backdrop, this study prioritizes the analysis of extreme heat intensity rather than mean temperature trends. Accordingly, a comprehensive spatiotemporal assessment of heatwave magnitudes across Türkiye is conducted for the 1950–2024 period, using the HeatWave Magnitude Index daily (HWMId) derived from daily maximum temperatures obtained from the ERA5-Land reanalysis dataset. The resulting time series reveal a robust upward trend in heatwave magnitude, characterized by a progressive escalation in annual mean values. Quantitative analysis establishes a baseline mean HWMId of 1.68 for the reference period. While the pre-2000 era was dominated by a low-magnitude regime, with annual averages largely remaining below 1.6, the post-2010 period marks a clear regime shift, frequently sustaining annual averages nearly 100% higher than the historical baseline. Specifically, the summer of 2023 experienced an unprecedented increase in severity, with the spatially averaged HWMId reaching approximately 10.5 marking an increase of more than 5 times the reference period mean. In contrast, although seasonal mean temperatures peaked in the summer of 2024, the corresponding HWMId exhibited only a 60% increase above the reference period. These findings indicate that the magnitude of extreme heatwaves is not always highly correlated with record-breaking seasonal mean temperatures, suggesting that extreme heat events are evolving into a more acute and non-linear phase. Overall, these results point to a fundamental shift in the regional climate regime, underscoring the urgent need for enhanced predictive capabilities and robust adaptation strategies.