Projected harmful algal bloom frequency in the Yangtze River Estuary and adjacent waters

Harmful algal blooms (HABs) are a frequent occurrence in China's offshore waters due to climate change and human activity, particularly in the Yangtze River Estuary and adjacent waters. Here, we studied HABs and their relationship with climatic and environmental factors in these waters from 1979 to 2016 using historical observations and reanalysis data. We then projected HABs frequency under various climate scenarios using the "environmental impact factor-frequency of HABs" mathematical model built using the BP neural network method and CIMP5 model data (RCP 2.6, RCP 4.5, and RCP 8.5). The results suggest a significant positive correlation between HABs frequency and seawater nutrient concentration, winter sea surface temperature, and low-wind days, and HABs frequency is anticipated to increase significantly by the 2040s compared with that of the historical era. Furthermore, future phytoplankton conditions are predicted to favor HAB species.