Analysis of water surface changes in Arga Island (the Lena Delta), based on remote sensing data

Recent climate change has led to an acceleration of permafrost melting in Arctic regions, causing significant landscape transformations through thermokarst processes. This study focuses on water surface dynamics in Arga Island (the Lena Delta), by analyzing satellite imagery from Sentinel-2 (2019-2024) and topographical data. We used a multi-method approach that combined median composite generation, spectral indices (MNDWI, NDVI, and Tasseled Cap), and supervised classification to quantify changes in water bodies and soil moisture. We also used the topographic position index (TPI), derived from the ArcticDEM data, to contextualize these changes within areas prone to thermokarst processes. The results indicate stable areas of water bodies over a six-year period with no significant changes in size (e.g., an area of 388 km2 in depressions in 2019 versus 390 km2 in 2024). However, an analysis of the MNDWI values between 2019 and 2024 has revealed localized moisture increases in upland areas, suggesting the emergence of thermokarst hotspots. These areas, which are characterized by positive TPI values and rising wetness indices, may represent early stages of degradation. Methodologically, the study demonstrates the effectiveness of cloud-based platforms, such as Google Earth Engine, for processing medium-resolution images. However, longer time series and higher resolution data are required to detect subtle trends. The use of spectral indices and topographic metrics in conjunction provides a reproducible framework for monitoring thermokarst activity in Arctic regions.