# 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 grassland ecosystems, drought was identified as the primary factor contributing to the reduction in GPP, with the PRQ effect causing an average decrease of \(1.62\) gC/m\({}^{2}\)/day. The secondary factor was extremely high temperatures, with the TR effect leading to a reduction of \(0.6^{7}\) gC/m\({}^{2}\)/day in grassland GPP. The influences of R and Q (atmosphere humidity) can be considered negligible. In forest ecosystems, the changes in GPP during the CHD event were determined by multiple factors. High temperatures had a robust limiting effect on tree GPP, resulting in an average decrease of \(0.82\) gCm\({}^{2}\)/day. Compared to grasslands, R and Q were more important climate factors for forests. High radiation caused an average increase of \(0.26\) gC/m\({}^{2}\)/day in GPP, and local atmosphere humidity led to a rise of \(0.14\) gC/m\({}^{2}\)/day in GPP. Figure 8 shows the contributions of different variables to the GPP changes. The difference between the _Control_ experiment and the _SE_Clim_ experiment represents the total effect (TPRQ) of CHD events, and the proportions of the effects of P (precipitation), T, R, and Q on the total effect are calculated. The residual terms are treated as the confounding or nonlinear effects between variables. In grassland ecosystems, insufficient precipitation emerges as the primary driver of the GPP decline, accounting for \(56\%\) to \(90\%\) of GPP anomalies observed in different events. Conversely, high temperatures contribute modestly,  
Figure 7: Regionally and temporally averaged changes in gross primary productivity (GPP) derived from the results from the _Control_ experiment and sensitivity experiments No. 2 to 8 relative to the _SE_Clim_ in (**a**) all affected areas, (**b**) grasslands, and (**c**) woodlands during the four CHD events. The boxes show the average GPP changes across different scenarios; the whiskers indicate the 25 th to 75 th percentiles of change. In each case (**a–c**), the average value of the four CHD events is written above the respective experiment. The combined effects of multiple factors are denoted as TPRQ (temperature, precipitation, radiation, and humidity), PRQ (precipitation, radiation, and humidity), RQ (radiation and humidity), and TR (temperature and radiation), while individual effects are represented by T (temperature), P (precipitation), R (radiation), and Q (humidity). “Grasslands” and “woodlands” refer to grid cells with over \(60\%\) grass and over \(60\%\) trees and shrubs, respectively. explaining 13% to 32% of GPP anomalies, while radiation and humidity effects remain generally negligible. High-latitude forests demonstrate that the inhibitory effect of extremely high temperatures on tree GPP can account for over 33% of GPP anomalies across various events. In contrast, water limitation resulting from meteorological drought may not pose a severe threat to trees, contingent upon drought intensity and species resilience, with local atmospheric humidity conditions exerting some influence. The effects of residual terms cannot be neglected in CHD events. In Case2017 and Case2010, the residual terms significantly negatively contribute to GPP changes, explaining 12% and 28% of GPP anomalies, respectively. Compared to grassland ecosystems, the impact of residual terms on GPP changes is greater in forest ecosystems.