Analysis of the water color transitional change in Qinghai Lake during the past 35 years observed from Landsat and MODIS

Abstract

Study region: Qinghai Lake, Qinghai-Tibet Plateau, China Study focus: Water color has been recognized as an essential climate variable for lakes and oceans. Forel-Ule index (FUI), as one representative water color quantization parameter, is a useful indicator that shows water turbidity variations in lakes. In this study, the time series of FUI images were constructed for Qinghai Lake, the largest salt water lake in China, from 1986 to 2020 based on Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) data. The multi-source satellite data were first evaluated and compared with regard to the derivation of FUI; then, the spatial and temporal variations of water color in Qinghai Lake and its driving forces were analyzed. New hydrological insights for the region: The results revealed that the FUI showed a significant decreasing trend in Qinghai Lake from 1986 to 2004 and a significant increasing trend from 2004 to 2020, which temporally coincided with the water level variations in Qinghai Lake. The water level, water temperature, precipitation, and runoff were strongly correlated with the changes of FUI (correlation coefficients of 0.65–0.78). The substantial increases in precipitation and water temperature after 2004 can be the major causes for the transitional increase of water color in Qinghai Lake. This reflects one response mode of water quality in lakes to climate change.

Keywords

• Qinghai Lake
• FUI
• Water color
• Long-term change
• Climate change