## 4 Results and Discussion
### Projected Heatwave Changes in the 21 st Century
#### 4.1.1 Temporal-Spatial Heatwave Changes in the 21 st Century
Under RCP 8.5 (Figure 4b), the spatial characteristics are similar to those of RCP4.5. The Tibetan plateau will still experience a larger increase in HWDI in comparison with other regions under RCP8.5 than under RCP4.5. There are some similar characteristics for HWDI and T_HW increase pattern over the Tibetan Plateau under the two scenarios. For HWDI, the increase amplitude of Tibetan Plateau is much larger after the middle of the 21 st century, and Tibetan Plateau ranks highest on the change of HWDI after the 2050s under RCP8.5. For T_HW, under RCP4.5, the change of T_HW in Tibetan Plateau is in middle level in comparison with other regions at the early and middle of 21 st century and will rank only second to Northwest China after the 2080s, while under RCP8.5, the increase of T_HW in the Tibetan Plateau closely follows Northwest China before the 2030s, then the increasement over this region is rather close to Northwest China and it is projected to be the region with the largest increment after the 2080s. This result implies that the increment of HWDI over the Tibetan Plateau is larger than that of T_HW in comparison with other regions. Thus, the heatwaves will be more extreme with a higher value of HWDI. In addition, the Tibetan Plateau is more sensitive than other regions to climate warming in the middle and later of the 21 st century. For N_HW, the spatial pattern is similar under the two scenarios, with the largest increase of N_HW occuring in Northwest China, followed by North China and Central China, and South China the least. Regarding the projection of heatwaves, our analysis shows that China will experience more intense, more persistent and more frequent heatwaves. In general, this result is consistent with previous works [14; 54; 55]. In terms of spatial pattern for HWDI over Xinjiang Province, although there is a slight difference between the result presented and results from [PERSON] et al. [14] both illustrate that the south part of the Tibetan Plateau and Xinjiang have the largest increase rate for HWDI. The spatial pattern for HWDI over southern China and eastern China is obviously different from the result in [PERSON] et al. [11]. Different from the high increase rate along the coastal area and over southwest China in [PERSON] et al., the increasing magnitude of HWDI over these regions in our work is very small in comparison with other regions. Under RCP4.5, the increase rate of HWDI is also remarkably lower than the result in [PERSON] et al. [14] over most of China. We believe the CMIP5 model and spatial resolution are the possible reasons  
Figure 4: Temporal variation of zonal average HWDI anomaly (**a,b**), N_HW anomaly (**c,d**), and T_HW (**e,f**) under scenario RCP4.5 (left: **a,c,e**) and RCP8.5 (right: **b,d,f**) relative to the reference period of _1961–1990_ over China climate regions. The symbols on the line represent the significant linear trend of time series (star-filled red: positive trend at the 0.05 significance level; star filled blue: negative trend at the 0.05 significance level). for the difference between HWDI spatial patterns. In addition, among the different scenarios, our result for HWDI increase rate is significantly lower than the results under A2, A1B and B1 scenarios (9.0, 7.4 and 3.52 days/10a) [56]. Based on NEX-GDDP high-resolution projections, our results with a spatial resolution of 0.25\({}^{\circ}\) could present more spatial information for the HWDI change. For example, though the work of [PERSON] et al. [14] also indicate that the south part of Tibetan Plateau and southwest of Xinjiang will experience the more increasement of HWDI over China, however, the results in Figure 3a,b clearly show that the southern part of Tibetan Plateau will experience much higher increases than Xinjiang for HWDI and the increasing rate over the northern part of Xinjiang is much lower than that over the southern part of Xinjiang Province.