Sentinel-Based Inventory of Thermokarst Lakes and Ponds Across Permafrost Landscapes on the Qinghai-Tibet Plateau

Thermokarst lakes and ponds (hereafter referred to as thaw lakes) play an important role in the permafrost regions by regulating hydrology, ecology, and biogeochemistry. However, detailed quantitative information on thaw lake extent and distribution remains poorly resolved across the entire permafrost regions on the Qinghai-Tibet Plateau (QTP). Here, we applied the random forest (RF) model and manual visual vectorization methods to extract thaw lake boundaries on the QTP based on Sentinel-2 images. Accuracy assessment was comprehensively demonstrated regarding the inherent spatial resolution of imagery and RF model performance. The results showed that the accumulated uncertainty of the total thaw lake area was +/- 5.75 km(2), and the mean accuracy (91.9%) from field-measured boundaries of 132 thaw lakes supported the accuracy of this inventory. A total of similar to 161,300 thaw lakes with sizes ranging from 500 m(2) to 3 km(2) were detected, with a total area of similar to 2,825.45 +/- 5.75 km(2). Most thaw lakes were detected in the continuous permafrost type (94.1%) and within the elevations of 4,500-5,000 m (68.4%). The small thaw lakes (<10,000 m(2)) predominated the total lake number (78.9%) but contributed to a small portion of the total lake area (12.7%). Spatial distributions of thaw lakes in terms of different climatic and environmental conditions were also comprehensively explored, including temperature, precipitation, ground thermal stability, active layer thickness, vegetation, soil properties, and underground ice content. This inventory is expected to be incorporated into Earth system models for a more comprehensive projection of the large-scale biogeochemical feedback of thermokarst landforms on the QTP under continued global warming. Plain Language Summary Thaw lakes develop when warming soil melts ground ice, causing the surface to collapse and form pools of water. Such lakes can greatly influence local water resources and ecosystems, but also are important sources of greenhouse gas released into the atmosphere. Using Sentinel-2 images, we provided robust information of thaw lake numbers, areas, and spatial distributions across the entire QTP permafrost regions by applying the random forest model and manual visual vectorization methods. The accuracy of the data set has been demonstrated in regard to the image spatial resolution, model performance, and field-measured results. Within sizes ranging from 500 m(2) to 3 km(2), we extracted similar to 161,300 thaw lakes with a total area of similar to 2,825.45 +/- 5.75 km(2). We found that most thaw lakes were located in the continuous permafrost regions and within the elevations of 4,500-5,000 m. Most thaw lake sizes were smaller than 10,000 m(2) but they only contributed to a little percentage of the total lake area. We also comprehensively explored the spatial distributions of thaw lakes in different climatic and environmental areas. This inventory would be useful for future Earth system models to predict the large-scale biogeochemical feedback of thaw lakes on the Qinghai-Tibet Plateau in the future.

Automated summary

Thaw lakes are important in permafrost regions for regulating hydrology, ecology, and biogeochemistry. This study successfully extracted thaw lake boundaries in the Qinghai-Tibet Plateau using the random forest model and manual visual vectorization methods, providing accurate information on the total area and distribution of thaw lakes. The inventory of thaw lakes is expected to contribute to Earth system models for a more comprehensive projection of their biogeochemical feedback under continued global warming.