Emergy-based accounting for historical and future water-related ecosystem services of tropical rainforest national park

• Accounting framework of WESs in tropical rainforest national parks is established. • WESs simulation model of WESs under human-nature coupling system is constructed. • TWESs in HTRNP declined 22.24% from 2000 to 2023. • The TWESs are expected the largest increase (2.56%) during 2023–2060 under SSP126. Tropical rainforests provide abundant water-related ecosystem services (WESs). However, under the integrated pressures of climate change and human activities, global tropical rainforests face severe deforestation and degradation, posing significant threats to the WESs. Accurate accounting of WESs in tropical rainforests is critical for their conservation and management. Existing accounting methods for WESs in tropical rainforests face challenges, such as subjectivity due to human preferences and the fact that the calculated monetary value does not equal market value or transaction value. Therefore, this study developed an emergy-based accounting framework for WESs in tropical rainforest national parks and established a simulation model for WESs under a coupled human-natural system. Taking Hainan Tropical Rainforest National Park (HTRNP) as a case study, this study counted and simulated the WESs for the periods 2000–2023 and 2025–2060, respectively. The results suggest that: (1) the total WESs of the HTRNP exhibited an overall declining trend from 2000 to 2023, decreasing from 3.51E + 20 sej/yr to 2.73E + 20 sej/yr representing a 22.24% reduction. Spatially, the distribution displayed a distinct “east-high-west-low” pattern; (2) the average proportions of sub-categories of total WESs during 2000–2023 were microclimate regulation service (52.29%), hydrological regulation service (46.25%), water resources supply service (38.86%), and water purification service (0.09%); (3) the total WESs are projected to increase under the sustainability and high-emission scenarios (SSP126 and SSP585, increasing by 2.56% and 1.47% by 2060, respectively), while declining under others, most severely under SSP370 (−14.29%). Furthermore, SSP126 supports over 26.79%, 12.11%, and 4.98% of water resource supply, hydrological regulation, and water purification services than other high-emission scenarios by 2060. These results quantify the tangible benefits of sustainable pathways for securing water-related benefits from the national park. This study provides a scientific foundation for the conservation and management of WESs in the HTRNP.