Abstract
The opportunities of retrieving geospatial datasets as open data and the reliability of Free and Open Source Software (FOSS) GIS increased the possibilities of performing a large number of geospatial analyses. In particular, the worldwide availability of Digital Elevation Model (DEM) permits to compute several topographic indexes able to characterize the land morphology.In this paper, we evaluate the performances of different open source GIS in the calculation of the Topographic Wetness Index (TWI), a widespread index in hydrological analysis that describes the tendency of an area to accumulate water. Nowadays, there is a large number of available open source desktop GIS, maintained as FOSS projects, each of them focusing on developing specific goals. Therefore, from user point of view, the choice of the best software in solving a particular task is influenced by the GIS specific features.The test was performed computing the TWI for the Rio Sinigo basin, in northern Italy. The DEM of the test area has been processed with GRASS GIS, Whitebox GAT and SAGA GIS. In order to identify equal workflows, all the combinations of available algorithms and parameters have been studied for each considered GIS. The final TWI maps produced as output were compared and discussed.
Highlights
The natural processes occurring in a catchment landscape can be analyzed by studying its topography
The identification of the common path was quite straightforward for System for Automated Geoscientific Analyses (SAGA) Geographic Information Systems (GIS) and Whitebox Geospatial Analysis Tools (GAT), while it was harder for Geographic Resource Analysis Support System (GRASS) GIS, which calculates the Topographic Wetness Index (TWI) with a one-step tool, without clarifying or documenting the implemented algorithms
The algorithms have been grouped in four categories, considering the three main phases for the TWI computation and the one step procedure, in order to highlight the differences in the algorithms availability and the degree of freedom of choice given to the user
Summary
The natural processes occurring in a catchment landscape can be analyzed by studying its topography. This analysis can provide information on the geomorphology, hydrogeology and even on biological processes taking place in the basin, leading to a qualitative, and quantitative, characterization of the area. The spatial distribution of topographic attributes provides an indirect measure of the spatial variability of the processes taking place in the catchment and, makes it possible to map them. It is possible to divide these topographic attributes in primary and secondary topographic indexes. The primary topographic indexes are those that can be directly obtained from the elevation data, whilst the secondary topographic indexes are combinations of the
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