Application of Sentinel-2 MSI optical data for snow cover monitoring in the Vitosha mountain region of Bulgaria

The following study presents results derived by the ongoing research project "Monitoring of the seasonal dynamics and stability of the snow cover in the mountain range of the Republic of Bulgaria for a period of 10 years (2014-2024) based on Remote Sensing". The Vitosha mountain region situated in Bulgaria (278 km2) was used as a test area for monitoring Snow Cover Extent (SCE) for an eight-year period (2016-2023). The results derived by the conducted study consist of SCE information which is crucial part of the calculation of Snow Water Equivalent (SWE), hydrological runoff modeling and flood forecasting and monitoring. In the present research the available cloudless optical data of Sentinel-2 MSI, generated and exported from Google Earth Engine (GEE), from October to May, for the period between 2016 and 2023 were used for snow cover monitoring purposes. Normalized Differential Snow Index (NDSI) and Snow Water Index (SWI) were calculated, and the resulting output raster datasets were post-processed and inspected additionally to obtain threshold classifications used for calculation of snow cover area distribution. Global Warming and Climate Change with its negative effects, such as frequent droughts, water scarcity in the summers, and less-snow winters, have a significant impact on agriculture, hydrology, forests, and ecology in Bulgaria. The results obtained in the study can be used and integrated for observations and studies of climate change at the local and regional level.