Ecosystem Services Tradeoffs and Synergies Across Drought Gradients in the Middle Reaches of the Yellow River Basin: A Time Scale Perspective

In the context of global climate change, understanding the tradeoffs and synergies between ecosystem services (ESs) is essential for regional ecological management and sustainable development. This study simulated net primary productivity (NPP) and quick flow (QF) in the Middle Reaches of the Yellow River Basin (MRYRB) in 2000 and 2020, utilizing the Carnegie–Ames–Stanford Approach (CASA) and Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) models to assess ESs related to carbon sequestration (CS) and water yield (WY). The synergistic multi-temporal scale changes in ESs tradeoffs under different drought conditions were assessed by delineating regions with different drought frequencies. The results showed that (1) the mean NPP in the MRYRB increased from 189.03 g C/m² in 2000 to 335.94 g C/m² in 2020, reflecting a 77.71% rise, while the mean annual QF escalated from 41.20 mm in 2000 to 59.59 mm in 2020, marking an increase of 44.64%; (2) on a monthly scale, the tradeoff and synergy relationships exhibited distinct seasonal variations, with tradeoffs prevailing throughout the year and a shift from tradeoff to synergy in CS and WY during the summer and fall. On an annual scale, synergy was the dominant relationship; (3) the intensity of tradeoffs and synergies varied by drought gradients, with the highest intensity observed in high-frequency drought areas at the monthly scale, whereas, on an annual scale, low-frequency drought areas exhibited the strongest tradeoffs and synergies. This study provides an in-depth analysis of the interactions between ESs under varying drought conditions across different time scales. The findings highlight the distinct differences in tradeoffs and synergies of ESs, offering valuable scientific insights for the coordinated management of regional ecosystems.