Cardiovascular diseases attributed to future heat and cold: A projection study of climate change impact under different scenarios in an arid region of Iran, Esfarayen.

Climate and temperature changes are among the most critical challenges for human and planetary health; however, evidence on future temperature-related health impacts remains limited in the Middle East and other arid regions. This study quantified historical and projected heat and cold-related cardiovascular morbidity (i.e., hospital admissions) in an arid region of Iran under multiple climate, population, and adaptation scenarios. Daily cardiovascular disease counts were associated with temperature using a quasi-Poisson regression within a distributed lag non-linear model (DLNM), which was then combined with historical and projected temperature data (1981-2099) obtained from the ISIMIP database under RCP2.6, RCP4.5, and RCP8.5 scenarios. In addition to station-based observations, air temperature was predicted using land surface temperature (LST) within a semi-parametric regression framework. Population change was incorporated using United Nations low- and high-fertility variant scenarios. Adaptation was modeled as a 20% upward shift in the minimum-CVDs temperature and compared with a no-adaptation scenario. Results showed that heat-attributable cardiovascular morbidity is projected to increase by more than 30% in several mid- and late-century decades, particularly under RCP8.5, whereas cold-attributable morbidity remains negligible (< 1%) and highly uncertain. Adaptation and population change had low effects on the attributable fraction, while the use of LST-derived air temperature resulted in more conservative risk estimates compared to station-based data. These findings highlight substantial future heat-related cardiovascular risks and emphasize the need for heat-specific urban planning and improved exposure modeling in projection studies, especially in arid regions.