## 1 Introduction
Compared to tropical natural forests, tropical plantation forests have relatively homogeneous ecological environments and stand structures, making them advantageous entry points for studying the carbon cycle in tropical forests. Moreover, research has shown that as representative species of tropical plantation forests, rubber plantation forests have a carbon sequestration capacity per unit area that exceeds that of natural forests [24]. Hainan Island (18\({}^{\circ}\)10\({}^{\prime}\)-20\({}^{\circ}\)10\({}^{\prime}\) N and 108\({}^{\circ}\)37\({}^{\prime}\)-111\({}^{\circ}\)03\({}^{\prime}\) E) covers an area of about 35,400 km\({}^{2}\) and is the largest tropical island in China [30]. _Hewea brasiliensis_ plantations are extensively scattered across the island, especially concentrated in the northwest and central mountainous areas, occupying approximately 20 percent of the area of Hainan Island [31]. In addition, after the introduction of _Hewea brasiliensis_ to Hainan, there was a relative scarcity of water and heat conditions, causing a reliance on typhoons to bring precipitation that was concentrated in July to September, accounting for 70% of the total yearly precipitation [32]. _Hewea brasiliensis_ transpiration is strong, especially during the rubber production period. Coupled with the topography and geology of Hainan Island, which causes difficulty in storing large amounts of precipitation for short periods, the rubber plantations in Hainan will also face serious drought impacts [33]. It has been confirmed that the huge water consumption caused by the powerful transpiration of rubber trees in the rainy season exceeds that of other land cover types, and the water deficit caused by a drought seriously affects the carbon sequestration capacity of the natural rubber plantation ecosystem [34; 35]. Therefore, it is a necessary to investigate the effects of droughs on the carbon dynamics of rubber plantation ecosystems. Current studies have investigated the carbon cycle of rubber plantations in Hainan and Xishuangbanna through a series of methods, including biomass inventories, eddy covariance observations, and remote sensing inversion [31; 36]. They have also further discussed the carbon cycling and carbon balance processes of the natural rubber plantation ecosystem under differentiated conditions, such as climate, planting patterns, and stand age. Present studies have researched the vulnerability of GPP of _Hevea brasiliensis_ plantations to regional flash drought responses, using changes in GPP as an indicator of drought impacts [37]. Furthermore, the causes of drought in natural rubber plantation ecosystems have been carefully researched [38], as well as the drought resistance mechanisms of rubber natural rubber plantation ecosystems [39]. Against the background of future climate change, the frequency, intensity, and duration of droughs will increase, which will inevitably affect tropical forests. Based on calibrated SEIB-DGVM, used to simulate the response of rubber forest GPP in multiple drought scenarios, the sensitivity and vulnerability characteristics of natural rubber plantation ecosystems in response to different drought characteristics were quantified and clarified. In the existing studies, SEIB-DGVM has exhibited good performance in simulations at the site, intercontinental, and global scales [40], and there have been studies that have improved the simulation performance of the model through parameter optimization [41]. Moreover, by enabling flexible selection of vegetation life and phenological characteristics and allowing the activation or deactivation of plant function types (PFTs), the model has demonstrated the ability to generate simulations covering various ecosystems such as the Malaysian tropical rainforest and eastern Siberian larch forest [42]. Research on the sensitivity and vulnerability of natural rubber plantation ecosystems to droughs can help predict the impact of droughs on tropical plantation ecosystems and the change trend of tropical plantation ecosystems in future climates.