Climate change projections of heatwaves in Valencia (Spain) using a heat index analysis

The increasing duration and intensity of heatwaves have become a growing concern due to their implications for health, economy and agronomy. The data from the reference period 1950-2017 from different studies around the globe indicates an average increase of 1 day per decade in heatwave duration and between 2 and 6 °C per decade in intensity. This phenomenon is particularly evident in cities such as Valencia and other locations in the Mediterranean region, where extreme temperatures have reached record levels. In Valencia, for example, the highest temperature in its history was recorded in 2023, at 46.8 °C.

The objective of this contribution is to project trends for heatwaves by estimating various features, such as their duration, intensity, and cumulative impact, using heat index (HI) as a key metric to evaluate the risk and the degree of exposure associated with these extreme events in the Mediterranean city of Valencia. The analysis applies daily maximum temperature and relative humidity data for the period 1979 to 2100 from five global climate models of the CMIP6 (GFDL-ESM4, IPSL-CM6A-LR, MPI-ESM1.2-HR, MRI-ESM2-0, UKESM1-0-LL) and historical observations (1979-2014), processed with ERA5-Land grids (~9 km) and classified by climate change scenarios defined in the IPCC Sixth Assessment Report. Heatwave intensity was assessed using the HI, which combines temperature and humidity to estimate thermal sensation and its effects on health.

Since 2010, heatwaves have shown a significant increase in duration and intensity in Valencia. Between 2011 and 2013, the total number of heatwave days exceeded 25 days per year, with intensity peaks above 50 °C. Climate models reflect similar trends to historical trends, with MPI-ESM1-2-HR showing the closest alignment to the historical trend.

In the climate change analysis period from 2014 to 2100, the SSP370 and SSP585 scenarios show a more accelerated increase in exposed days and extreme heat values, with the most pronounced trends occurring after 2055. In contrast, the SSP126 scenario suggests stagnation in the duration and intensity of heatwaves at 2014 levels in some models. However, projections from models such as IPSL-CM6A-LR and MRI-ESM2-0 indicate persistently high values throughout the period, highlighting variations in model responses even under the same scenario.

The results highlight the rising trends in the intensity and duration of heatwaves in Valencia, clearly illustrating their progression over time in the context of climate change and the increasing frequency of extreme events. The use of the HI as a metric underscores its implications for human health and well-being. These findings emphasize the need for adaptive and preventive measures to address the growing impacts of heatwaves on the most vulnerable populations, especially in the Mediterranean cities.  

Acknowledgements:

This study has received funding from the: “THE HUT project” (The Human-Tech Nexus – Building a Safe Haven to cope with Climate Extremes), under the European Union’s horizon research and innovation programme (GA No. 101073957).