## 5 Conclusions  
This paper projects the changes of the heatwave and population exposure over China during the 21 st century and at 1.5 \({}^{\circ}\)C and 2.0 \({}^{\circ}\)C global warming under RCP4.5 and RCP8.5 scenarios by using Multi-Mode Ensemble (MME) results based on ten CMIP5 models with a spatial resolution of 0.25\({}^{\circ}\) from NASA-GDDP. The major conclusions about heatwaves can be summarized as follows:  
1. Heatwaves are projected to become more extreme (1.07 days/decade and 2.90 days/decade for HWDI), more frequent (0.40/decade and 1.26/decade for N_HW) as well as longer-lasting (3.78 days/decade and 14.59 days/decade for T_HW) over China under RCP4.5 and RCP8.5, respectively, with significant spatial variation.
2. The spatial pattern of three heatwave indices is similar under the two scenarios while the increase will be considerably intensified under RCP8.5. From a zonal perspective, the high-resolution CMIP5 projections show that high latitude and high altitude regions, e.g., the Tibetan Plateau and northern China, are projected to experience a larger increase in intensity, frequency and the total duration of heatwaves than that in southern China (except for Central China).
3. According to NEX-GDDP 25 km heatwave projections, the total population affected by heatwaves is projected to significantly increase and will reach 1.18 billion in the middle and later part the 21 st century based on.the 2010 population density map. In addition, more and more people will suffer a longer duration of total annual heatwaves in the 21 st century.
4. Compared with 2.0 \({}^{\circ}\)C global warming, holding the global warming below 1.5 \({}^{\circ}\)C can largely reduce the threat of the heatwaves, with HWDI decreasing by 26.9% and 29.1%, N_HW decreasing by 34.7% and 39.64% as well as T_HW decreasing by 35.3% and 40.10% under RCP4.5 and RCP8.5, respectively.
5. Population exposure will be 1.07-1.10 billion and 1.153 billion for 1.5 \({}^{\circ}\)C and 2.0 \({}^{\circ}\)C warming climates, respectively. The half-degree less of warming will not only reduce the population exposure by 83-53 million but also greatly reduce the threat caused by longer heatwave exposure under both the RCP4.5 and RCP8.5 scenarios.  
With the CMIP5 MME projections at 25 km spatial resolution, this study could provide more comprehensive information about heatwaves and population exposure under two RCP scenarios in the 21 st century, especially for 1.5 \({}^{\circ}\)C and 2.0 \({}^{\circ}\)C warming cases. Compared with the rural areas, the urban areas are more sensitive and vulnerable to heatwaves. Therefore, further works should focus on the heatwave risk for the city agglomeration, which in the future will have more population and social-economic activities.  
[PERSON] and [PERSON] designed this Manuscript; [PERSON] provided the data; [PERSON] processed the data and wrote this manuscript; [PERSON], [PERSON] and [PERSON] modified and polished this manuscript; [PERSON] and [PERSON], funding acquisition; [PERSON] supervision.  
This research was funded by the National Natural Science Foundation of China, grant number 71461010701 and 41701385.  
This research paper was conducted at Department of Hydraulic Engineering, Tsinghua University. Thanks also to NASA for providing NEX-GDDP CMIP5 dataset.  
The authors declare no conflict of interest.