Spatiotemporal Dynamics and Time–Frequency Driving Responses of Fractional Vegetation Cover for Riparian Ecological Sustainability in Bengbu Section of Huaihe River Basin

Fractional vegetation cover (FVC) is a core indicator for evaluating ecological environment quality, soil conservation capacity and riparian ecosystem sustainability. Using 30 m Landsat time-series data spanning 2011–2025, this study classified FVC into five grades. The Theil–Sen median slope estimation, Mann–Kendall significance test, univariate linear regression, and wavelet coherence method were applied to investigate spatiotemporal dynamics and time–frequency coupling responses of multi-grade FVC to the driving factors of sustainable ecological governance. Results demonstrated that 63.4% of the area exhibited stable vegetation coverage, 28.3% presented significant improvement, and only 8.3% suffered degradation. Spatially, high- and medium-high-FVC areas were concentrated in the riparian ecological zone, artificial forests, and agricultural land; while low-FVC areas were concentrated in urban and industrial zones. Linear regression evidenced a statistically significant increasing trend for high-FVC areas (R2 = 0.304, p = 0.033), whereas low-FVC areas presented non-significant long-term monotonic variation (R2 = 0.079, p = 0.309). The results of wavelet transform coherence tests revealed that high-FVC areas maintained persistent in-phase synchronous coupling with agricultural irrigation volume on a two-year cycle, and exhibited anti-phase lagged oscillations against total water resource volume. Low-FVC areas were sensitive to agricultural irrigation volume, and the influences of total water resources volume and annual precipitation on FVC were time-varying rather than persistent. This study provides a quantitative theoretical and methodological support for sustainable ecological spatial management and riverbank buffer zone construction in similar urbanized river basins.