Spatial-temporal water area monitoring of the Miyun Reservoir using remote sensing imagery from 1984 to 2020

Miyun Reservoir has produced huge benefits in flood control, agricultural irrigation, power generation, aquaculture, tourism, and urban water supply. Accurate water mapping is of great significance to the ecological environment monitoring of the Miyun Reservoir and the management of the South-to-North Water Diversion Project. The purpose of this research is to design a long-term dynamic water mapping method for the Miyun Reservoir by solving difficult problems such as cloud and snow interference, terrain shadows, and mixed pixels encountered in the mapping to realize the analysis and monitoring of water surface information changes in the Miyun Reservoir. The research successfully applied the tasselled cap transformation to the cloud detection of Landsat series data. DEM data are used to remove terrain shadows during processing. The water index WI, which is very suitable for long-term dynamic mapping, is introduced for water extraction, and the local unmixing method is used to make the extracted water contours and subpixel small targets more accurate. In addition, the research innovatively uses the landscape separation index to conduct a macroscopic analysis of the water surface morphology of the Miyun Reservoir. The algorithm in this paper has completed the dynamic water map of the Miyun Reservoir from 1984 to 2020, and the accuracy of the mapping result is high. The overall accuracy of direct verification is 98.2% under the condition of no clouds and snow, which is comparable to the existing water system map product (improved FROM-GLC). The overall consistency of cross-validation is as high as 99.4%. In addition, a long-term analysis of water surface information, such as the area, coverage, and morphological characteristics of the Miyun Reservoir, has been performed. (1) The area of Miyun Reservoir changed tremendously during the 37 years from 1984 to 2020, with the largest being 151.6 km2 and the smallest being 57.3 km2. The area changes are mainly concentrated in three areas, including the northern area, the area where the Chao and Bai Rivers enter the reservoir, and the island in the center of the reservoir. (2) Based on the changes in the area of Miyun Reservoir, it is divided into five periods: “growth” (1984—1993), “peak” (1994—1999), “decline” (2000—2003), “protection” (2004—2014), and “recovery” (2015—2020). (3) The changes in Miyun Reservoir during one year mainly occurred in 4 areas, including the northern area, the area where the Chao River enters the reservoir, the island in the center of the reservoir, and the West Stone Camel subdam area. Due to the release of water from the reservoir in May before the arrival of the rainy season each year, the area is the smallest. The area reached the largest in a year at the end of the rainy season in August or September because a large amount of rainwater was accumulated. (4) The Miyun Reservoir’s landscape separation changed greatly during the 37 years. When the water volume is small, it splits into two reservoir areas in the east and west. The east and west reservoirs underwent a process of three divisions and three consolidations from 1984 to 2020. The three split periods include 1984—1986, 2003—2005, and 2014—2015, and the other years are in the consolidation period. © 2023 Science Press. All rights reserved.