Abstract
A heat danger day is defined as an extreme when the heat stress index (a
combined temperature and humidity measure) exceeding 41 ℃, warranting
public heat alerts. This study assesses future heat risk (i.e., heat
danger days times the population at risk) based on the latest Coupled
Model Intercomparison Project phase 6 (CMIP6) projections. In recent
decades (1995-2014) China’s urban agglomerations (Beijing-Tianjin-Hebei,
Yangtze River Delta, Middle Yangtze River, Chongqing-Chengdu, and Pearl
River Delta) experienced no more than 3 heat danger days per year, but
this number is projected to increase to 3-13 days during the population
explosion period (2041-2060) under the high-emission pathways (SSP3-7.0
and SSP5-8.5). This increase will result in approximately 260 million
people in these agglomerations facing more than 3 heat danger days
annually, accounting for 19% of the total population of China, and will
double the current level of overall heat risk. During the period
2081-2100, there will be 8-67 heat danger days per year, 60-90% of the
urban agglomerations will exceed the current baseline number, and nearly
310 million people (39% of the total China population) will be exposed
to the danger, with the overall heat risk exceeding 18 times the present
level. The greatest risk is projected in the Pearl River Delta region
with 67 heat danger days to occur annually under SSP5-8.5. With 65
million people (68% of the total population) experiencing increased
heat danger days, the overall heat risk in the region will swell by a
factor of 50. Conversely, under the low-emission pathways (SSP1-2.6 and
SSP2-4.5), the annual heat danger days will remain similar to the
present level or increase slightly. The result indicates the need to
develop strategic plans to avoid the increased heat risk of urban
agglomerations under high emission-population pathways.