Spatial frequency analysis of hydrogeomorphic events in Northwest Namibia based on over two decades of satellite Earth observation
- Author(s)
- Janek Walk, Bruno Boemke, Florian Betz, Moshe Armon, Joel Mohren, Julian Krieger, Frank Lehmkuhl
- Abstract
Rare but heavy precipitation events are the fundamental driver for geomorphic activity in arid regions. A quantification of the frequency and magnitude of episodic discharge is essential for a robust characterization of flood hazards and better understanding of the poorly studied hydromorphodynamics in deserts. However, observation data from both precipitation and stream gauges often are sparsely distributed and/or do not cover a sufficiently long seamless time series. This applies, for instance, to the remote Northwest Namibia, where more than a dozen ephemeral rivers drain the Kunene Highlands towards the Skeleton Coast, yet daily river flow data for a period of several decades is only available from the Hoanib. Therefore, we apply spatial frequency analyses on time series of (i) the IMERG (V06) precipitation product since 2000 (temporal resolution: 30 min; spatial resolution: 0.1°) and (ii) the Landsat multispectral satellite imagery archive since 1999 (temporal resolution: 16 d; spatial resolution: 30 m) in order to generate spatially resolved recurrence intervals for pluvial events and floods of different magnitudes, respectively. While pluvial events are analysed for the entire catchment areas in the Kunene Region, a refined spatial aggregation of stream and floodplain sections is used for the hydrogeomorphic frequency analysis. To cater for the limitations of the Landsat imagery related to the 16-day-revisit time, we calculate spectral indices allowing for the detection of both inundated areas during flooding (e.g., NDWI) and effects sustained after flood recession (e.g., NDVI). As a novel approach, we implement the hydrogeomorphic frequency analysis directly in the Google Earth Engine environment after attributing the spectral imprints of floods to their magnitudes. For this purpose, a statistical relationship is developed between the daily record of the gauging station at the Hoanib and the multispectral surface characteristics along the river course – before transferring this relationship to the other ephemeral streams.
- Organisation(s)
- Department of Geography and Regional Research
- External organisation(s)
- Katholische Universität Eichstätt-Ingolstadt (KU), Stanford University, Eidgenössische Technische Hochschule Zürich, Rheinisch-Westfälische Technische Hochschule Aachen, Universität zu Köln
- Publication date
- 2023
- Austrian Fields of Science 2012
- 105404 Geomorphology, 207402 Remote sensing, 105902 Natural hazards
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/97df410d-69dc-4944-9f62-cacb42c93571