Research on the early warning indicator system for red tide disasters in the nearshore sea area in Qinhuangdao

Abstract In order to construct an early warning indicator system for red tide disasters in the nearshore sea area of Haigang District in Qinhuangdao, this study analyzes data collected from online buoy monitoring from April to October 2024, including temperature, salinity, chlorophyll-a, pH, turbidity, nitrate, and dissolved oxygen (DO) data, along with red tide information from monitoring based on satellite remote sensing. The results indicated that during the monitoring period, red tides occurred 16 times, with a cumulative duration of 55 days and a total affected area of 10,047 km 2 . The typical duration and affected area of a single red tide ranged from 1 to 2 days and 195 to 850 km 2 , respectively. The occurrence of red tides in the nearshore sea area of Haigang District is associated with environmental factors such as chlorophyll-a, nitrate, DO and its range, among others. Taking each environmental factor as an early warning indicator for red tides, both chlorophyll-a and nitrate showed an increasing trend in missing alarm rate (MAR) with the increase in the red tide incidence. The study results showed that red tides in the nearshore sea area of Haigang District present the characteristics of high frequency, long durations, and large average areas from late summer to early autumn (August to October). The DO range and nitrate are reliable early warning factors of red tide occurrence in the sea area.