Anthropogenic emissions and urbanization increase risks of compound hot extremes in cities

Most areas of the world are experiencing increasing and intensifying hot extremes. Heat-related health consequences vary with the characteristics of the exposed landscape and types of hot extreme.

Despite mounting evidence of detrimental health impacts from hot days or nights due to their high intensity and/or long duration, their occurrence in close sequence - a compound hot extreme - has received little attention but may bear large health risks.

A new study published in Nature Climate Change revealed how the compound (day-night sustained) hot extremes affect human health, as well as the drivers of observed changes, and future risk in cities of eastern China.

The study showed that compound hot extremes were more dangerous than solely daytime or nighttime heat, especially to female and older urban residents.

Urban compound hot extremes across eastern China increased by 1.76 days per decade from 1961 to 2014, and the fingerprints of urbanization and anthropogenic emissions (e.g., greenhouse gases and aerosols) could be detected.

Their attributable fractions were estimated as 0.51 (urbanization), 1.63 (greenhouse gases) and -0.54 (other anthropogenic forcings) days per decade. Future emissions and urbanization would make these compound events two-to-five times more frequent (2090s vs. 2010s), leading to a threefold-to-sixfold growth in urban population exposure.

"Our study reveals that the public health risks from anthropogenic increases in compound hot extremes have been increasing and will continue to increase over cities in eastern China." Said Dr. Jun Wang from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences, the first author of the study. 

According to the study, the uncovered age-specific vulnerability to compound hot extremes implies further elevated health burdens due to rapid ageing of the urban population there.

This study was supported jointly by the National Key Research and Development Programme of China and the Strategic Priority Research Program of the Chinese Academy of Sciences.