## 3 Results
### The Sensitivity and Vulnerability of GPP to Initiation Season of Drought  
As shown in Figure 4, there were differences in the sensitivity of GPP to droughts occurring in different drought initiation seasons. In drought scenarios dominated by precipitation scarcity, the sensitivity of GPP to droughts occurring in the early rainy season ranged from a maximum of 0.655 to a minimum of 0.003; for droughts occurring in the peak rainy season, the sensitivity of GPP ranged from a maximum of 0.554 to a minimum of 0.01; and for droughts occurring in the early dry season, the sensitivity of GPP ranged from a max value of 0.748 to a min value of \(-\)0.023. Overall, GPP was generally more sensitive to droughts occurring in the early rainy season (Figure 4a-d). In contrast, the sensitivity of GPP to droughts occurring in the peak rainy season was relatively lower (Figure 4e-h). Although the sensitivity in most scenarios of droughts occurring in the early dry season was relatively low, there were specific drought scenarios with exceptionally high sensitivity, and these scenarios tended to exhibit a higher sensitivity to flash droughts than gradual droughts (Figure 4i-l). In drought scenarios dominated by high temperatures, the sensitivity of GPP to droughts occurring in the early rainy season ranged from a maximum of 0.687 to a minimum of \(-\)0.013; for droughts occurring in the peak rainy season, the sensitivity of GPP ranged from a maximum of 0.363 to a minimum of 0.001; and for droughts occurring in the early dry season, the sensitivity of GPP ranged from a maximum of 0.001 to a minimum of \(-\)0.062. When the intensity and duration of the drought were consistent, GPP remained more sensitive to droughts occurring in the early rainy season, with a higher sensitivity to flash droughts than gradual droughts (Figure 5a-d). The sensitivity to most drought scenarios occurring in the peak rainy season and early dry season was generally lower (Figure 5e-l). Figure 3: SEIB-DGVM localization results. (**a**) Timeseries of GPP_Est and GPP_Obs from 2010 to 2015; (**b**) scatter plot of GPP_Est and GPP_Obs from 2010 to 2015. The vulnerability of GPP to droughs in different initiation seasons of drought is also different. In drought scenarios dominated by precipitation scarcity, the vulnerability exhibited by GPP to droughs occurring in the early rainy season ranged from a maximum of 0.949 to a minimum of 0.003; for droughs occurring in the peak rainy season, the vulnerability exhibited by GPP ranged from a maximum of 0.987 to a minimum of 0.01; and for droughs occurring in the early dry season, the vulnerability exhibited by GPP ranged from a maximum of 0.961 to a minimum of \(-0.014\). Based on the vulnerability depicted in Figure 6, holistically, droughs occurring in the early rainy season and early dry season resulted in higher losses to GPP compared to droughs occurring in the peak rainy season across more drought scenarios. According to the performance of GPP vulnerability, flash droughs caused greater losses to GPP. Figure 4: Under the Premin and Tmin scenarios, intensity = \(-0.75\), initiation season in April (**a**); August (**e**); December (**i**). Intensity = \(-1.25\), initiation season in April (**b**); August (**f**); December (**j**). Intensity = \(-1.75\), initiation season in April (**c**); August (**g**); December (**k**). Intensity = \(-2\), initiation season in April (**d**); August (**h**); December (**l**). The sensitivity of GPP varies with the duration of the drought and the SPEI time scale. Figure 5: Under the Tmax and Premax scenarios, intensity = \(-0.75\), initiation season in April (**a**); August (**e**); December (**i**). Intensity = \(-1.25\), initiation season in April (**b**); August (**f**); December (**j**). Intensity = \(-1.75\), initiation season in April (**c**); August (**g**); December (**k**). Intensity = \(-2\), initiation season in April (**d**); August (**h**); December (**l**). The sensitivity of GPP varies with the duration of the drought and the SPEI time scale.