Drivers of shifts in ecosystem carbon sink and water yield trends before and after the establishment of national key ecological function zones in China

• A novel model-based quantification of NKEFZs’ impacts on carbon-water services. • Post-implementation, NEP growth rate nearly tripled while water yield rose. • Vegetation restoration and wetter conditions drove simultaneous NEP and WY gains. • The NEKFZ policy contributed 37% of the NEP increase after its implementation. Enhancing net ecosystem productivity (NEP) and water yield (WY) services is critical for sustainable ecosystem management and water security. In 2010, China established National Key Ecological Function Zones (NKEFZs) to restore ecosystems; however, their impact on carbon–water service dynamics remains poorly quantified. Using a calibrated process-based model (CEVSA-ES), we assessed the effects of vegetation restoration (greening and vegetation type changes) and global climate changes (climate change, elevated CO 2 , and nitrogen deposition) on the shifts in NEP and WY trends relative to NKEFZ implementation. Over 2001–2021, both NEP and WY exhibited increasing trends (5.1 Tg C yr –2 and 0.3 mm yr –1 , respectively), and were the most evident in the water and soil conservation zones, biodiversity maintenance zones, and water conservation zones, respectively. Notably, following the NKEFZs establishment, NEP growth accelerated remarkably from 1.9 Tg C yr –2 (2001–2010) to 5.6 Tg C yr –2 (2011–2021), particularly within water conservation zones, whereas WY trends reversed from a decline (–0.5 mm yr –1 ) to an increase (0.9 mm yr –1 ). While greening drove NEP growth and precipitation governed WY changes during 2001–2021, the post-2010 NEP acceleration was jointly controlled by vegetation restoration and global climate change, Conversely, the WY trend reversal was primarily attributed to shifts in precipitation trends. These findings provide critical insights into how ecological policies can synergistically enhance carbon and water services under a changing climate, offering important implications for sustainable ecological restoration and natural climate solutions.