Carbon and water relationships change nonlinearly along elevation gradient in the Qinghai Tibet Plateau

The influence of terrain elevation on carbon and water ecosystem services, mediated by heat and energy redistribution, has significant implications for the Qinghai Tibet Plateau (QTP). Renowned as the “Third Pole of the Earth” and the “Water Tower of Asia,” the QTP boasts the planet’s most extensive elevation range. However, understanding the intricate effects of the elevation gradient (EG) on carbon and water services and their interrelationships remains limited. In this study, we deploy the moving window method (MWM), the generalized additive model (GAM), and the structural equation model (SEM) to explain the dynamics of ecosystem service relationship across the EG. Our analysis, spanning 2000 to 2018, reveals annual mean values of carbon storage (CS) at 50.45 tC/ha and water yield (WY) at 246.14 mm for the QTP. The results highlight the importance of the carbon-water trade-off and the pronounced CS reduction in the south-central plateau under varying EG, alongside the harmonized interactions in the northeast and southern sectors. GAM outcomes show a non-linear association between ecosystem service relationship and EG. With elevational ascent, the correlation between the digital elevation model (DEM) and CS transitions from positive to negative, and the ecosystem service relationship transitions from synergy to trade-off. In the QTP, the explanatory force of inherent meteorological factors in shaping CS and WY surpasses that of all socio-economic factors, with the latter wielding greater influence over ecosystem service relationship dynamics. The insights from this investigation provide a foundation for integrating intricate terrain gradients into strategies aimed at alleviating potential adverse ramifications for human well-being.