Long-Term Records Reveal Temperature-Driven Nutrient Limitation and Predict Intensified Algal Blooms in Global Lakes

Harmful algal blooms (HABs) are an escalating global threat to aquatic ecosystems, reducing biodiversity, degrading water quality, and compromising human health. Climate-driven warming and excessive nutrient inputs are key drivers of HABs in global lakes. However, as nutrient reduction strategies gain traction, the relative contributions of rising water temperatures and nutrient enrichment remain unclear. Here, we compiled a dataset spanning 40 years from 156 lakes worldwide and analyzed the nonlinear response relationship between chlorophyll-a (Chl-a) and water temperature using a combination of empirical mode decomposition (EMD) and a random forest (RF) model. EMD demonstrated strong adaptability in extracting long-term stable signals from non-stationary records, revealing that over 40% of the lakes are eutrophic, with substantial spatial heterogeneity in HAB intensity; mean Chl-a concentrations reached as high as 26 μg L^-1 in tropical regions. As warming continues, water temperature emerges as a progressively stronger driver of HABs, surpassing the influences of nutrient availability and stoichiometric balance. Rising water temperatures diminish the reliance of HABs on nutrient availability, while the nitrogen-to-phosphorus ratio consistently explains variation in Chl-a concentrations throughout the warming process. Furthermore, RF-based scenario projections indicate that under current warming and nutrient scenarios, the mean annual Chl-a concentrations of global lakes are projected to rise to 17.7 μg L^-1 under RCP 4.5 and 18.4 μg L^-1 under RCP 8.5 by the end of the 21st century. These findings highlight the urgent need to incorporate temperature effects into lake HAB management strategies.