Analyzing the carbon sink dynamics in the Qinling–Daba Mountains and their asymmetric response to precipitation anomalies using an improved CASA model

Qinling–Daba Mountains. Mountain ecosystems play a crucial role in the global carbon cycle and climate regulation, but their dynamic carbon sink responses to increasingly variable precipitation patterns remain poorly understood. To address this, we used the kernel normalized difference vegetation index to drive the Carnegie–Ames–Stanford Approach (CASA) model in simulating net primary productivity, and further calculated net ecosystem productivity (NEP) by subtracting soil heterotrophic respiration. The study systematically analyzed the evolution of carbon sinks in the Qinling–Daba Mountains from 2001 to 2023 across different vegetation types, characterized the asymmetric responses of carbon sinks to precipitation anomalies using the asymmetric index, and employed a Random Forest model to evaluate the relative impacts of environmental factors on carbon sink asymmetry. During the study period, the regional NEP showed an overall upward trend, with a growth rate of 4.10 g C·m⁻²·yr⁻¹ and a cumulative carbon gain of 53.12 Tg C, the carbon sink centroid shifting northeastward. Croplands and forests served as the dominant and continuously strengthening carbon sinks. NEP exhibited a negative asymmetric response to precipitation, indicating that carbon losses during drought years exceeded carbon gains in wet years. Leaf area index emerged as the primary driver of this asymmetry, followed by ecosystem carbon sequestration potential and elevation. These results advance the understanding of mountain carbon sink dynamics under changing precipitation conditions. • kNDVI as a driver enhances the reliability of CASA model simulations. • The centroid of the carbon sink in the study area exhibited a northeastward shift. • Carbon sinks display a negative asymmetric response to precipitation anomalies.