Remotely sensed water turbidity dynamics and its potential driving factors in Wuhan, an urbanizing city of China

Understanding of turbidity, an indicator of water quality, is of great importance in cities and can have significant implications for human society. Many users are interested in mapping turbidity using remote sensing tools for long-term and large-scale monitoring. This study aims to derive turbidity maps in an urbanizing city and to identify the driving factors for better decision-making and water quality management. Taking Wuhan, the most rapidly urbanizing metropolis in central China, as an instance, the water turbidity is monitored using Landsat observations from 1987 to 2019, and the relationships of turbidity and climatic/human factors are examined. Climatic factors are represented by meteorological conditions (rainfall, wind speed, temperature, and water vapor pressure) and human factors are characterized by the normalized difference vegetation index (NDVI) and impervious surface area (ISA). The results demonstrated that: (1) the seasonal mean turbidity increased from spring to summer (34.28 NTU to 36.27 NTU), decreased in autumn (25.04 NTU), and increased again in winter (37.20 NTU), and the variations were related to changes in rainfall; and (2) the annual mean turbidity was fluctuatingly stable during 1987–2004 and decreased by 1 NTU/yr. since 2005. The decline of water turbidity was highly correlated to the increase of NDVI and ISA with p values < 0.01. The study indicates that meteorological conditions affect seasonal variations in turbidity, while human factors have long-term impacts. A cautious approach to human activities during urbanization is needed to achieve a balance between water quality protection and the city’s developments.