Monitoring Surface Water Change in Northeast China in 1999–2020: Evidence from Satellite Observation and Refined Classification

As a typical region with high water demand for agricultural production, understanding the spatiotemporal surface water changes in Northeast China is critical for water resources management and sustainable development. However, the long-term variation characteristics of surface water of different water body types in Northeast China remain rarely explored. This study investigated how surface water bodies of different types (e.g., lake, reservoir, river, coastal aquaculture, marsh wetland, ephemeral water) changed during 1999–2020 in Northeast China based on various remote sensing-based datasets. The results showed that surface water in Northeast China grew dramatically in the past two decades, with an equivalent area increasing from 24 394 km² in 1999 to 34 595 km² in 2020. The surge of ephemeral water is the primary driver of surface water expansion, which could ascribe to shifted precipitation pattern. Marsh wetlands, rivers, and reservoirs experienced a similar trend, with an approximate 20% increase at the interdecadal scale. By contrast, coastal aquacultures and natural lakes remain relatively stable. This study is expected to provide a more comprehensive investigation of the surface water variability in Northeast China and has important practical significance for the scientific management of different types of surface water.