Lake Water Color Dynamics, Environmental Drivers, and Optical Responses in Arid Northwest China: A 42-Year Landsat-Based Analysis

Lake water color provides an integrated indicator of aquatic environmental change, yet its long-term phenology and resilience remain poorly understood in arid regions. In this study, Landsat-derived hue angle (α) records were reconstructed for 350 lakes larger than 1 km2 across arid Northwest China from 1984 to 2025. Regional mean α declined significantly over the past 42 years (R2 = 0.51), accompanied by pronounced spatial heterogeneity. Three lake water color phenological types were identified: Aseasonal (75.0%), Summer Greening (13.7%), and Spring Greening (11.3%). Aseasonal lakes were the most stable, whereas seasonal lakes showed greater temporal variability and a tendency to transition toward aseasonality. Lake water color resilience increased in 43% of lakes, declined in 21%, and remained unchanged in 36%, with resilience-loss lakes showing distinct spatial clustering. Lake morphology was most strongly associated with water color change, topography and thermal conditions with its phenology, and watershed population dynamics with its resilience. In situ observations further showed significant relationships between α and optically active constituents and their derived parameters, reflecting the combined optical effects of absorption and scattering and suggesting its potential as a proxy for broader water-quality assessment with more extensive field sampling and validation. These findings highlight contrasting controls on lake-color dynamics, phenology, and resilience, and demonstrate the value of hue angle for monitoring environmental change in vulnerable arid-zone lakes. Overall, these results advance understanding of the long-term environmental responses of arid-zone lakes and provide a scientific basis for targeted monitoring and adaptive management in arid regions.