Detection and Attribution of Changes in Thermal Discomfort over China during 1961-2014 and Future Projections

In this study, variation in the frequency of thermal discomfort days over China during the period of 1961-2014, including heat discomfort days (HDDs) and cold discomfort days (CDDs), and the influence of external forcings on it are discussed. HDDs are the conditions of overheating and overhumidity (represented by humidity index), and CDDs reflect the dangers from cold temperatures and winds (represented by wind chill index). Observations show significant increases (decreases) in the frequency of HDDs (CDDs) over China from 1961 to 2014, with clear regional distinctions. The historical ALL and greenhouse gas (GHG) simulations can sufficiently reproduce the spatial patterns of the observational trend in the frequency of both HDDs and CDDs over China. Further, the impacts of GHG and anthropogenic forcings on the HDDs (CDDs) are detectable over China, except for central and eastern China, based on the optimal fingerprinting method. GHG forcing is identified as a dominant factor for the observational changes in the frequency of HDDs over southern China; GHG and anthropogenic forcings have dominant effects on the variation in the frequency of CDDs over southwestern China. Although trends in the frequency of HDDs and CDDs in historical aerosol forcing simulations seems to be opposite to observations, an aerosol signal fails to be detected. Natural forcing contributes to the observational variation in the frequency of HDDs over northwestern China. In addition, the future projections of thermal discomfort days indicate that Chinese residents will face more threats of heat discomfort and fewer threats of cold discomfort in the future under global warming.