## 3 Results
### The Impact of CDHEs on GPP in Rubber Plantations  
As shown in Figure 4, the trend of the probability of GPP loss for rubber plantations in Hainan Island under different compound drought and heatwave scenarios from April to November. As CDHEs intensified, the probability of GPP loss in rubber plantations increased significantly in April and May. In contrast, the trend of the probability of GPP loss from June to November was completely opposite to that of April and May, decreasing progressively from mild to extreme events. The probability of GPP loss peaked in May, reaching 0.554, 0.585, 0.612, and 0.645 under mild compound drought and heatwave (MCDH), moderate compound drought and heatwave (ModCDH), severe compound drought and heatwave (SCDH), and extreme compound drought and heatwave (ECDH) scenarios, respectively. In contrast, October showed the lowest probability, with values of 0.388, 0.320, 0.265, and 0.198 for the same scenarios.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Copula** & **Squared Euclidean Distance (d)** \\ \hline [PERSON] & 0.1521 \\ [PERSON] & 0.1521 \\ [PERSON] & 0.1806 \\ [PERSON] & 0.1422 \\ T & 0.1754 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Goodness-of-fit evaluation results for SPEI-3 and STI-1.  
Figure 3: Time series of the monthly CDHI. The shaded areas in the background represent real drought and heatwave events. The dashed line represents the CDHE threshold (CDHI = \(-0.5\)).  
The Probability of GPP Loss Under Different Scenarios of Drought, Heatwave, and Compound Drought and Heatwave  
As shown in Figure 5, the probability of GPP loss in rubber plantations varied under different scenarios of heatwaves, drought, and compound drought and heatwaves from April to November. As shown in Figure 5a, the median probability of GPP loss was 0.549, 0.529, and 0.553 under mild heatwave (MH), mild drought (MD), and MCDH scenarios, respectively, in May. In July, these probabilities were 0.444, 0.460, and 0.487 for the same scenarios. These results indicate that the probability of GPP loss under the MCDH scenario was higher than under either the MH or MD scenario alone in May and July. However, this pattern was reversed in other months. As shown in Figure 5a-c, the probability of GPP loss in rubber plantations increased as the intensity of heatwaves increased in April, May, June, August, and October, while it decreased in other months. Similarly, droughts led to an increase in the probability of GPP loss in April, May, and November, while it decreased from June to October. Overall, the median probability of GPP loss under the severe heatwave (SH) scenario reached its highest value (0.719) in April among all SH scenarios from April to November. Similarly, the severe drought (SD) scenario showed its peak (0.638) in April, while the SCDH scenario peaked in May (0.612), when compared to their respective scenarios over the same period.  
Figure 4: The centroid movement curve of the probability of GPP loss in rubber plantations on Hainan Island from April to November under different compound drought and heatwave scenarios. MCDH: mild compound drought and heatwave; ModCDH: moderate compound drought and heatwave; SCDH: severe compound drought and heatwave; ECDH: extreme compound drought and heatwave.