Spatial and temporal changes in plant water supply obtained by NDVI in Tinja and Kozlica watersheds

Abstract

Normalized Difference Vegetation Index (NDVI) is an indicator of vegetation health and land cover changes, based on the reflectance of certain ranges in the electromagnetic spectrum. Land use, seasons and climate changes affect spatial variations in NDVI values. This study focuses on the basins of the rivers Tinja and Kozlica, located on the Eastern parts of the Maljen Mountain, and characterized by the dominant presence of grassy vegetation. Spatial and temporal changes in plant water supply are monitored using 10-meter Sentinel-2 imagery, and further processed on a monthly basis in QGIS for 2020-2021. For better elaboration of NDVI values basins of these two rivers were delineated into 305 sub-basins, on which further analysis was performed. NDVI data during both years range from < 0.1 - > 0.6. NDVI values change during different seasons, which is consistent with the increase and decrease of water stress during the studied period, which refers to changes in weather conditions during the growing season. In the summer months, the highest values exceed 0.6, and in some cases even 0.8. NDVI values in October and November decrease to 0.3 and 0.5, while in winter months NDVI values are <0.1. NDVI values are higher, and less variable, in sub-basins with woody, partially coniferous vegetation. This study contributes to increasing knowledge about the potential application of remote sensing as well as highresolution Sentinel-2 imagery for monitoring plant water supply because the assessment of drought impact on plant production requires the current monitoring of plant water regime. GIS tools enable the delineation of sub-catchments, which helps to better monitor the spatial variation of NDVI within natural landscape entities. NDVI and other indices are easy to calculate, and therefore, Sentinel-2 can play an important role in future drought early warning systemsand in determining conditions of the vegetation cover.