Borderless heat hazards with bordered impacts

This paper sets out to demonstrate that there are large deficiencies in reporting of heatwave impacts in international disasters databases, international organization reports, and climate bulletins. The study uses the ERA5-HEAT reanalysis of the Universal Thermal Climate Index (UTCI) to provide  quantitative  evidence  of  the  areas  of  the  world  that  are  exposed  to  heat  stress  with a focus on the Northern Hemisphere. Although heatwaves are as  impactful  as  other  hazards,  reporting  their  characteristics  and  impacts,  as  well  as  understanding  their  risk  is  challenging  because  they  are  an  invisible  physical  phenomenon. Robust reporting is essential not only for communicating the risk of heatwaves, but also to develop effective policy and action.

This study indicates that heat stress is growing in area and is larger during the month of August. It also demonstrates that heatwaves are borderless not constrained by political boundaries and that impacts are not adequately reported—a deficiency in risk reporting. To start solving the discrepancies presented in the paper between heat stress exposure and impact reports, the study offers suggestions to address them while aiming at building the evidence base that is currently lacking, and putting in place the robust adaptation measures needed.