Effects of hydrological factors on the net primary productivity with a focus on precipitation, temperature, and groundwater storage

Understanding the relationship between the hydrological cycle and terrestrial carbon dynamics is vital for monitoring atmospheric CO2 fluxes and addressing climate change. Despite their importance, the effects of hydrological components on carbon fluxes remain unclear. This study aimed to estimate spatiotemporal net primary productivity (NPP), a key indicator of the CO2 sink capacity, and identify the role of hydrological factors in South Korea using the Carnegie-Ames-Stanford Approach (CASA) model. NPP in South Korea varied between 276.32 and 1,075.70 gCm−2 year−1, depending on the land cover type, with a mean value of approximately 751.93 gCm−2 year−1 between 2004 and 2019. Significant increases in NPP were primarily observed in deciduous broadleaf forest and cropland regions, whereas urban areas exhibited decreasing trends. Relative importance analysis of hydrological factors—precipitation, temperature, and groundwater storage (GWS)—revealed that higher temperatures and GWS during spring and autumn (i.e., the growing season) significantly increased vegetation NPP, while increased precipitation was the primary factor influencing NPP during the summer. In addition to the well-documented impacts of precipitation and temperature, this study thus highlights the critical role of groundwater in spatiotemporal NPP variation and enhances the understanding of the interaction between hydrological processes and carbon dynamics. Identifying the contribution of groundwater to CO2 sinks offers valuable insights for setting carbon flux monitoring strategies, particularly in ecosystems reliant on groundwater. These findings also illustrate the importance of integrating hydrological factors into climate change mitigation strategies.