[Extraction of land-cover and wetland area in Bohai Rim region based on Google Earth Engine.]

The land cover of Bohai Rim region has changed greatly due to urbanization and economic development. Monitoring the land cover with high accuracy and real time is the most important basis for relevant researches. Traditional single-machine processing mode is difficult to realize rapid monitoring for large-scale and long-time series. The emergence of remote sensing big data makes it possible to combine computing platform and massive data. The land cover maps of study area were interpreted based on Google Earth Engine (GEE) platform with decision tree (CART) method from 2000 to 2019. The land cover change was analyzed, and the interpretation results using different data sources were compared. The results showed that the GEE platform could realize the rapid land cover interpretation in a large area, which interpreted coastal wetlands and other cover types with high accuracy over 80% comparing the surveyed points. Compared with Landsat images, the Sentinel-2A images interpretation results had a great improvement in accuracy, which increased from 85% to 95%, and thus more detailed surface information could be reflected. In 2000, the area of wetland, build-up area, farmland, forest, and water in the study area were 1612.5, 5734.9, 32074.8, 11853 and 3504.3 km ² , accounting for 2.9%, 10.5%, 58.6%, 21.6% and 6.4% respectively. By 2019, wetlands had been reduced by 775.1 km ² , with a decline of 40.1%; built-up area increased by 5310.5 km ² with an increasing rate of 92.6%. The area of farmland, forestland and water area decreased 1841.6, 1823.5 and 870.3 km ² , with a decreasing rate of 5.7%, 24.8% and 48.1%, respectively. The coastal urbanization process caused the occupation of built-up area to other land use types, which was the main driving force of land cover change in the study area.