# Impacts of Compound Hot-Dry Events on Vegetation Productivity over Northern East Asia
## 3 Results
### Individual and Compound Effects of Hot and Dry Events  
In this part, the simulation results from the factor-controlled experiments by CLM5 are analyzed to disentangle the individual and combined effects of different meteorological factors on terrestrial ecosystems during CHD events. Here, we first show the combination effect of PRQ (precipitation, radiation, and humidity) to investigate the effect of drought with the effects of heat eliminated (panel a in Figure 5 and Figures S2-S6). The combination effect of RQ (radiation and humidity) excludes the effect of precipitation deficit (panel b in Figure 5 and Figures S2-S6). Since the radiation enhancement during the drought events due to cloudless air induces the increase in surface temperature, we show the combination effect of TR (temperature and radiation) and the individual effect of R (radiation) to investigate the impacts of heat and related solar radiation (panels c-d in Figure 5 and Figures S2-S6). The sole effect of T (temperature) on the spatial pattern of GPP changes can be deduced approximately based on the results of the effect of TR minus the effect of R. The results derived from the experiment of _SE_TR minus _SE_R_ show consistent spatial patterns of the GPP decreases compared to the experiment _SE_T minus _SE_Clin_ (Figure S7d), with their magnitude difference being less than 0.35 gC/m\({}^{2}\)/day. Figure 4: Changes in evapotranspiration (ET) (**a**), soil moisture (SM) (**b**), and gross primary productivity (GPP) (**c**) during the CHD events, calculated by subtracting the results of the _SE_Clin_ experiment from those of the _Control_ experiment. Figure 5 shows the GPP responses in northern East Asia. The results between the four factor-controlled experiments (_SE_PRQ_, _SE_RQ_, _SE_TR_, and _SE_R_) and the _SE_Clim_ experiment show that, except for Case2010, drought has a more significant effect on GPP than extremely high temperatures in the TCZ (Figure 5a,c). In the northern part of the region, the effects that exclude heat (PRQ, RQ, and R) consistently show an increase in GPP with similar magnitudes. However, the combined effect of temperature and radiation (TR) has a contrasting trend of GPP change. This suggests that while high solar radiation alone increases GPP, extremely high temperatures caused by high radiation can suppress GPP increase or induce a decrease in GPP. Compared to the combined stress of drought and heatwaves, shown in Figure 4c, the decline in GPP caused by individual droughs or heatwaves alone is smaller than the impact of heat-overlapping drought. Additionally, there is little difference between the combined effect of RQ and the individual effect of R (Figure 5b,d), indicating a slight contribution of near-surface humidity to GPP. This finding is consistent with the results from the experiment using abnormal forcing in 2 m air humidity only (Figure S8d). Figures S2-S6 show the synchronal changes in soil moisture, VPD, ET, canopy conductance (G\({}_{\rm c}\)), and the maximum carboxylation rate (V\({}_{\rm cmax}\)). These figures provide a visual representation of the data. Figure 6, on the other hand, presents the tabulated form, summarizing these changes concisely and in an organized manner. During drought, the soil moisture decreases prominently and extensively (Figure S2a). Heat also contributes to the decrease in soil moisture by enhancing ET (Figures S2c and S4c). Atmospheric dryness relates closely to abnormal heat (Figure S3c). Abnormal 2 m humidity plays a small but limited role in the increase in VPD, particularly in the TCZ (Figure S3b minus Figure S3d  
Figure 5: Changes in GPP caused by the combined effects of (**a**) precipitation, incident radiation, and 2 m humidity (PRQ), (**b**) incident radiation and 2 m humidity (RQ), and (**c**) 2 m temperature and incident radiation (TR) and (**d**) the individual effect of incident radiation (R) during the four CHD events.