Topographic Wetness Index, also known as the compound topographic index, (TWI) is a topographic indicator that calculates the potential of where water is likely to accumulate during excessive precipitation cycles resulting from abrupt atmospheric anomalies. High index values represent serious potential of water accumulation due to low slope, and the opposite for high slope. As expected from the term, slope, Digital Elevation Model (DEM) datasets play an important role in the calculation of TWI. DEMs are produced utilizing tachometry, GPS benchmarking, UAV, aerial or satellite image capture and LIDAR capabilities. However, no matter how it is generated, a DEM is as good as the actual ground sampling algorithm, on which the final resolution is based. Using six different DEM resolutions coming from three global and one national source presented in three different setting coverages, upper feeder basin of Bozkurt sub-province, Kastamonu, was analyzed emphasizing the urbanized part of the sub-province, which was devastated during the August 11th, 2021 flood. Coarser resolution missed the overall precision while the finer resolution captured it nicely. On the flip side, finer resolution excessively fragmented the questioned area while the coarser resolution formed a unity coinciding with the destructed area recorded during the event.

German Aerospace Center (DLR), EADS Astrium GmbH and Infoterra GmbH alliance came up with the idea of taking DTED-2 (Digital terrain elevation data, level-2) specifications to even higher standard of HRTE-3 (High resolution terrain elevation, level-3) in 2006, as a result TDX (TerraSAR-X, TanDEM-X) constellation was born. The mission was geared to create a rather sensitive, high precision 3 dimensional map of the entire Earth in seamless and very high quality. After Shuttle Radar Topography Mission (SRTM) in 2000 and its derivatives, along with numerous prior and subsequent other similar data, have practically set the standard for defining the topographical surfaces in global scale, the twin satellites acquired all of Earth’s land surfaces numerous times to produce varying resolution digital elevation models (DEM) between 2011 and late 2015. DEMs are widely used in many planning, decision making and engineering related projects. They provide sound backing for mankind’s endeavors. Ground resolution is the most sought after feature of any DEM. Finer resolution is usually associated with a better surface definition. Recently, an entirely new global DEM has been released DLR. The 90 m DEM is the latest variant derived from such an undertaking. This study aimed to examine the overall effectiveness of this alleged new data in four previously surveyed locations and against the performances of finer SRTM 1- and comparable SRTM 3 arc second data. The results showed that TanDEM-X 90 m data overestimated. They seemed to be rather accurate in flat to slightly undulating terrain, but overestimated in broken to treacherous terrain than both SRTMs. Root Mean Square Error was greater in site one and site four, and lower in site two and site three compared to both SRTM 1 and SRTM 3 arc second data.