How persistent and hazardous will extreme temperature events become in a warming Portugal?

Abstract

The impact of rising greenhouse gases (GHGs) in the atmosphere on the temperature distributions is felt not only in the mean values but primarily in the extremes. The temperature distributions are becoming slightly flattened and more broadened towards higher values, leading to a decrease in extreme cold events and more importantly to a considerable increase in the frequency and intensity of extreme hot events. These changes are no longer simple projections but are already occurring. It is thus imperative an assessment of the projected changes even under reduced emissions scenarios for the entire 21st century. In this study, a multi-variable ensemble based on 13 EURO-CORDEX high-resolution simulations at 0.11° resolution, was used to analyse the extreme heat events as well as the Universal Thermal Climate Index (UTCI) for such extremes between March and November over Portugal. The 13 simulations have in common three Representative Concentration Pathways (RCP), RCP2.6, RCP4.5 and RCP8.5 as well as data covering a historical period (1971–2000) and three future consecutive periods, 2011–2040, 2041–2070 and 2071–2 100. The results show that severe future heatwaves will develop beyond the extended summer months in all scenarios. Even under a high mitigation scenario (RCP2.6), the number of heatwaves will more than double in number, relative to the historical record. In the high emission scenario (RCP8.5), a sharp increase in the number, severity and areal extension of heatwaves is projected for the end of the 21st century. The analysis of the heat stress indicates that most of the projected future heatwaves will induce heat stress and the projected increase in areal extension and the number of occurrences will have an impact on morbidity and mortality rates simply due to the shear rise in the number of the affected population and the increased frequency of occurrence.