Analysis of environmental factors affecting the large-scale long-term sequence of green tide outbreaks in the Yellow Sea

Green tide outbreaks in the southern Yellow Sea have become an ecological disaster. To further understand the conditions of large-scale green tide outbreaks, this study examines the relationship between the expansion of green tides and environmental factors from 2007 to 2020. Using the Google Earth Engine (GEE) platform, the semi-automatic extraction of green tide information using multi-source satellite data was achieved for the first time. The normalized difference vegetation index threshold was determined manually according to the water environment and visual interpretation, and the automatic extraction of green tide information was realized based on GEE programming. The influences of the initial phase coverage area and growth rate of green tide algae on green tide outbreaks during 2007-2020 were explored. In addition, the sea surface temperature (SST), sea surface salinity, and precipitation (PRCP) during green tide outbreaks were systematically analyzed, and the influence of the combined effect of environmental factors on green tide outbreaks was also determined. The results showed that the initial scale of a green tide had no necessary influence on the outbreak scale; green tides were more likely to occur on a large scale if they were observed earlier in the initial phase, if the SST was lower, and if PRCP was timely and abundant. These findings are useful for further understanding the rules of green tide outbreaks, analyzing their outbreak conditions, and preventing and controlling green tide disasters