Isolating the Impacts of Land Use/Cover Change and Climate Change on the GPP in the Heihe River Basin of China

Terrestrial gross primary production (GPP) is a key indicator of the ecosystem response to climate change and land use/cover change (LUCC) in arid areas. The available global GPP data sets cannot meet the demands for local applications in arid areas due to sparse vegetation and extreme climate conditions. Here, we developed a novel GPP estimation model for the Heihe River Basin (HRB), the second largest inland river basin in northern China, and disentangled the impacts of climate change and LUCC on GPP. First, we calibrated the vegetation photosynthesis model (VPM) using CO₂ flux observations from multiple stations in the HRB and developed a modified local GPP model (HRB-VPM). Then, we decoupled the joint effects of LUCC and climate change on GPP based on the log and differential transformation method. The results showed that HRB-VPM outperformed Moderate Resolution Imaging Spectroradiometer and VPM GPP models in arid ecosystems. The root mean square error of HRB-VPM was 4.9 and 1.5 gCm⁻² day⁻¹ lower than those of the Moderate Resolution Imaging Spectroradiometer and VPM models, respectively. We concluded that the underlying driving forces of the GPP changes were distinct across the HRB. In the upper reach, climate change accounted for 65.8% of GPP changes, while in the middle and lower reaches, LUCC contributed to 75.1% of GPP changes. Our research provides an effective way to monitor arid ecosystem degradation and is useful for mitigating the negative impacts of human activities and future climate change.