A new improved mixed water index method: a case study of the Three-River Source Region

As an indispensable and vital water resource on Earth, surface water plays a pivotal role in maintaining ecological balance, supporting human activities, and driving economic development. However, against the backdrop of global climate change and intensifying human activities, surface water is confronted with serious challenges such as water pollution, reduction in area, and degradation of ecological functions. Thus, conducting dynamic monitoring of surface water bodies is of great reference value for water resource security and management, as well as ecological environment construction and restoration. This study takes the Sanjiangyuan region as an example and addresses the issue of the lack of long - time - series continuous water - body and glacier images in the area. By improving the methodology, it accurately extracts surface water bodies and glacier images, and analyzes the changes in water - body areas. The main research methods and results are as follows: <ol> <li>To solve the problem of the absence of long - time - series continuous water - body images in the Sanjiangyuan region, the study is based on the GEE platform and uses an improved mixed water index method to accurately extract and obtain water - body images from 1986 to 2023. This method effectively improves the accurate segmentation of water - land boundaries and the extraction of permanent water bodies under the condition of missing image data.</li><br/> <li>In response to the lack of long - time - series continuous glacier images in the Sanjiangyuan region, a method based on RGB image brightness recognition thresholds and known contour clipping is proposed. This method acquires long - time - series continuous annual - scale glacier images and completes the annual - scale statistics of glacier areas.</li><br/> <li>The changes in water - body areas in the Sanjiangyuan region can be divided into three stages. From 1986 to 1995, the water - body area first increased and then decreased. Specifically, from 1986 to 1989, there was a slight upward trend in water - body area. However, from 1990 to 1995, the water - body area gradually decreased, showing a slight downward trend overall during this period. From 1996 to 2012, the water - body area showed an overall upward trend, especially after 2000, with a more significant increase, reaching a peak of 14123.7 km² in 2005. Compared with 2012, the water - body area slightly decreased from 2013 to 2023, but overall, it was in a relatively stable fluctuation period. The water - body areas of different river basins and lakes show different changes due to different recharge modes, topography, and climate.</li> </ol>