The Interannual Variation And Risk Analysis Of Green Tide In The Yellow Sea

From 2007 to 2016, the large-scale floating green tides have consecutively occurred in the Yellow Sea of China for ten years, which have broken the balance of coastal marine ecosystems,caused huge economic loss to the local government, especially to the Shandong and Jiangsu provinces. Green tides were initially found along the Rudong and Yancheng coast of Jiangsu Province in May each year from MODIS images, with distribution of radial banded or patch-shaped. The green tides were floating north under the action of wind and current, and eventually developed into a large-scale green tide disaster.So, the study of interannual distribution variation of green tides in Yellow Sea is of great significance for understanding the process of ecological disaster, analyzing its economic and social losses, and has great importance for carrying out prediction 、 early warning and controlling.Based on the EOS/MODIS remote sensing ocean color data,the NDVI algorithm was adopted to inverse the distribution of green tides during Mar 1 and August 31. The green tides were firstly found from MODIS images in 2007 with the coverage area less than 50km2 in the Yellow Sea. Seasonally, the green tides first appeared during the middle of May to early June,then its coverage grew rapidly and continuously and reached a peak in 30-40 days. In July, the green tides depleted gradually and disappeared in August. The maximum coverage areas of the green tides were 3 110 km2 and 4 075 km2 in 2008 and 2009 respectively. The green tides coverages were in low phase from 2010 to 2012 and the peak areas in these past three years were less than 1 800km2. Since 2013, the scales of green tides increased rapidly, and the peak coverage reached 7 990 km2 in 2016. The green tides covered the regions ranged from 124°E in the east, Lianyungang of Jiangsu Province in the west, Rudong of Jiangsu province in the south and 37°N in the north. The trajectories of the green tides could be divided into three categories: (a) moved northward to 34°30’N, then turned to northwest toward the coast in 2008,2010 and 2011; (b) moved northward to 35°N,then drifted northeast parallel to the coast in 2009 and 2012; (c) moved northward to the coast of Shandong province, then turned along the coast in 2013, 2014 and 2015.The main affected area by the green-tide disaster in the South Yellow Sea was concentrated in 34.5°-35.75°N、 120.5°-121.5°E, with the area of 9 000 km2,and the extent of disaster surrounding the center area was gradually reduced. Qingdao, Rizhao and Rushan were the hard-hit coasts in Shandong province, and the green-tide disaster on Jiangsu Yancheng Coastal became more serious in the past four years.