Spatiotemporal variations in global lake clarity and responses to climate and landscape drivers

Water clarity, typically measured by the Secchi disk depth (SDD), is a critical factor influencing the functioning and development of lake ecosystems, yet the complex response of SDD to a warming world is not well understood. Here, we integrated Landsat-based modeling datasets and retrieved a time-series water SDD database by analyzing approximately 1.4 million satellite images. Covering the period from 1995 to 2023, this dataset provides insights into the SDD dynamics of 170,799 lakes larger than 1 km² worldwide. We show that 67% of the studied lakes have experienced a decreasing trend in SDD, with 39% exhibiting a statistically significant decline. Globally, lakes have experienced a 13% decrease in SDD. However, 44% of lakes in Asia demonstrate an increase in SDD. We propose that watershed climate, landscape influences, and in-lake algal blooms all exert significant impacts on changes in SDD. Climatic warming contributes to SDD decreases in North American and European lakes by promoting permafrost thaw and enhancing algal growth. Conversely, the observed increases in SDD in Asian lakes are primarily associated with the greening of surrounding landscapes. Our findings highlight the complex ways in which climate change affects lake SDD, emphasizing the combined roles of altered surrounding landscapes and in-lake algal growth in shaping these dynamics.