Multifaceted characteristics of summer heat and affected population across China under climate change

Excessive heat can cause discomfort, stress even mortality to humans. We investigate the multifaceted characteristics of summer heat and the affected population across China using a composite heat index (HI) based on meteorological observations and the Coupled Model Intercomparison Project Phase 6 climate models. We highlight that HI is only applicable when maximum air temperature is above 26.7 celcius. From 1961 to 2014, China has experienced increasing heat days (1.05 day/10a) and severity (0.15 celcius/10a) with more population influenced by expanding heat extent. Simultaneously, increases in the frequency (7.58-14.80 times), duration (0.46-1.23 days) and intensity (1.00-1.42 celcius/day) of heat events are detected with increased population exposure (9.33 x 10(5)-5.59 x 10(6) times center dot persons). In the future, increases in heat severity, spatial extent, and the affected population would be aggravated from 1.5 to 2 to 3 celcius warming. Dangerous heat events would experience increases in frequency (12.67-70.81 times), duration (0.85-7.21 days), intensity (1.78-8.57 celcius/day), and population exposure (2.06 x 10(6)-3.18 x 10(7) times center dot persons) under a warming climate. Some regions over the Tibetan Plateau and southwest China would be affected by expanding cautionary and extremely cautionary heat. Northwest China would experience intensified dangerous heat events whereas southeastern China would face longer-lasting heat events with stronger intensity. Precautionary strategies are essential for these regions under risk.