Topography effect on land cover in a river basin system: Case of Bystrytsia Pidbuzka

Анотація

Topography is an important factor of land cover. Concurrently, topography and land cover are significant hydrological regime controls of an area, which, for the purpose of water management, is represented as a basin system – a network of subbasins connected by the streamflow. Therefore, this study aims at providing a simple methodology for an automated delineation of a river basin system, and for its subsequent geomorphometric and land cover characterization using available global geodatasets.

As a case, we chose the Bystrytsia Pidbuzka basin system of 500 km², which has a transitional location between the Carpathian Mountains and the Fore-Carpathian Upland in Lviv Oblast (Ukraine). Global digital elevation model (DEM) FABDEM V1-2 with a resolution of 30*30 m was used as a primary geodataset for topography data, while ESA WorldCover V2 2021 with a resolution of 10*10 m was selected as a primary land cover geodataset. Firstly, we automatically delineated the basin system by applying hydrology analysis algorithms to the DEM. Secondly, we used a zonal function to obtain the main geomorphometric indices (mean and standard deviation values of altitude and slope) for each subbasin. Thirdly, an agglomerative cluster analysis was applied on the indices to group the subbasins into several topography classes. We also postprocessed the land cover geodataset and calculated proportions of land cover classes in each subbasin via a tabulate area function. Then, we used the cluster analysis to group the subbasins into land cover classes. Finally, correlation coefficients between geomorphometric and land cover indices of the subbasins were calculated.

The Bystrytsia Pidbuzka basin system consists of 21 subbasins of 4-6^th Strahler ranks with the area of 63–5 038 ha, mean altitude of 259–656 m, and mean slope of 0–13°. The subbasins form four distinct topography classes: 1. Flat plain subbasins; 2. Undulating plain subbasins; 3. Transitional plain-mountain subbasins; and 4. Mountain subbasins. The subbasins are also grouped into five classes according to prevailing land cover types: 1. Tree – grass; 2. Tree – grass – arable; 3. Tree – grass – arable – built; 4. Arable – tree – grass; and 5. Arable – grass – tree – built. We found the strongest correlation between altitude and slope indices (0.97) as well as between altitude / slope and tree cover (0.86). The weakest correlation is between slope and built-up areas (-0.17), which can be partly explained by underrepresentation of built-up areas on the WorldCover dataset.

Key words: basin system; topography; land cover; geomorphometry; FABDEM; ESA WorldCover; Carpathian Mountains; Fore-Carpathian Upland.