Global 250-m algal bloom frequency of large lakes from 2000 to 2021 (ABGL250_2000-2021)

The algal bloom defined in this product refers to the phenomenon of excessive growth of algae and the formation of algal scums on the water surface, which is expressed by the algal bloom frequency (unit: percentage). The algal bloom frequency refers to the ratio of the number of times identified as an algal bloom to the number of valid observations per year in each pixel. Algal blooms have a major impact on the lake water quality and the safety of drinking water for local communities. This product used MODIS-related data （MOD09GA、MOD09GQ、MOD10A1、MOD11A1） as data sources. After removing ice, turbid waters and aquatic vegetation areas by combining auxiliary data, the Floating Algae Index (FAI) was calculated for each pixel in the lake. The FAI threshold for algal bloom extraction was derived using the maximum gradient method to obtain the daily algal bloom extent in the lake. The ratio of the number of times identified as an algal bloom to the number of valid observations per year in each pixel was calculated to obtain this product.