Potential impact of climate change on heatwaves at the urban scale: An evaluation in Valencia, Spain

Global temperatures have risen rapidly over the past six decades, with the Mediterranean region recognized as a climate hotspot due to its accelerated warming and declining precipitation. In this context, heatwaves have become more frequent, longer, and more intense, causing growing risks to human health, ecosystems, and urban resilience. This study aims to quantify the historical (1979–2014) and projected (up to 2100) evolution of heatwaves in Valencia, Spain. Daily maximum temperatures (°C) and relative humidity (%) from five CMIP6 global climate models under three emission scenarios were used, complemented with observational records. The heat index is used to better assess the impact of heat on human health. Temporal trend analyses and spatial interpolation are applied to assess changes in frequency, duration and intensity. Results show that during 1979–2014, the heatwave frequency increased by approximately two events per decade, while their mean duration rose from under 10 to nearly 25 days. Under future scenarios, intensification continues: by mid-century frequency may increase by up, 3.6 additional events per decade, and toward the end of the century there seems to be shift toward a quasi-permanent heat season, as episodes merge into fewer but longer events. Rising humidity further amplifies thermal stress, enhancing the human health impact. Despite uncertainties inherent in climate projections, these findings highlight the need to revisit heatwave definitions refine thermal risk thresholds, and adopt robust adaptation strategies for Mediterranean cities. • Heatwaves in the Mediterranean region and in Valencia have risen since 1979 and are projected to increase in the future. • Warmer springs and longer autumns in Valencia will extend heatwave exposure. • Rising humidity and prolonged heatwaves enhances thermal stress intensifying health risk in Mediterranean cities. • Future heatwaves in the Mediterranean region are projected to merge into fewer, longer, and more persistent events.