Anthropogenic and climatic factors regulate algal bloom intensity and timing in global lakes under climate change

Algal blooms are becoming more frequent and intense in lakes worldwide, but how bloom intensity and timing co-vary at the global scale is unclear. Here we analyze two decades of Moderate Resolution Imaging Spectroradiometer satellite observations for 4085 lakes ( > 20 square kilometres) to compare changes in intensity (fractional floating algal cover) and timing (start and end dates) of surface algal bloom. We find that intensity and timing often change independently: about 71% of lakes show increasing intensity, mainly associated with higher population density and agricultural pressure, whereas temperature and wind better explain shifts in bloom timing, especially in cold regions. Under a medium-emission scenario, tropical lakes show rapid intensification with modest timing shifts, while cold-region lakes exhibit regionally contrasting timing changes. This decoupling may alter lake food webs and carbon cycling, underscoring the need for region-specific management strategies under climate change. Population density and agricultural activity intensify fractional floating algal cover in 71% global lakes, whereas temperature and wind regulate the bloom phenology, according to an analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) data across 4085 global lakes for two decades.