A Multi-Scale Assessment and Modeling of Water and Land Resources for Sustainability in the Lower Okavango River Basin: Integrating Climate Change, Land Use, and Hydrological Dynamics
von Kaleb Gizaw Negussie
Datum der mündl. Prüfung:2025-07-03
Erschienen:2025-07-11
Betreuer:Prof. Dr. Martin Kappas
Gutachter:Prof. Dr. Daniela Sauer
Gutachter:Dr. Daniel Wyss
Gutachter:Prof. Dr. Heiko Faust
Gutachter:Dr. Stephen Boahen Asabere
Gutachter:Dr. Michael Dietze
Gutachter:Dr. Birgitta Putzenlechner
Zum Verlinken/Zitieren:
http://dx.doi.org/10.53846/goediss-11371
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Name:Kaleb_Gizaw_Negussie_PhD_Dissertation_04.07.2025_.pdf
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Zusammenfassung
Englisch
This dissertation provides a multi-scale assessment and modeling of water and land resources within the Lower Okavango River Basin, aiming to foster sustainability by integrating the complex dynamics of climate change, land use changes, and hydrological responses. Water scarcity, climate change, and food insecurity are some of the challenges the world faces, which demand quick action and concerted efforts to achieve sustainable resource management, particularly in the arid and semi-arid environments of sub-Saharan Africa like the Okavango. The transboundary Okavango River basin located in the drylands of southern Angola, northeastern Namibia and northwestern Botswana, epitomizes the complex challenges of managing shared resources amongst pressures from climate extremes, rapid population growth, adverse land use practices. The research addresses critical knowledge gaps by sequentially evaluating hydrological model performance, projecting future hydro-climatic scenarios, and assessing land suitability for climate-resilient agriculture. This study emanated from limited comprehensive assessments exploring this catchment (Mendelsohn et al., 2002; Strohbach, 2008), and its dynamic response to different variables. Firstly, the Soil and Water Assessment Tool (SWAT) model's performance was evaluated for streamflow estimation in the semi-arid Okavango-Omatako catchment using high-resolution TanDEM-X DEM. The model was configured for a 31-year period from 1985 to 2015. Subsequently, calibration and validation processes followed using the SUFI-2 algorithm. SWAT demonstrated reasonable results in modelling semi-arid streamflow with high and low flows adequately captured, establishing its applicability for this data-scarce, flat terrain. The semi-arid characteristics together with relatively flat terrain features justified the need for the evaluation of model performance using discharge data in our study region. Secondly, the SWAT+ model was employed to assess the projected streamflow response of the lower Okavango River Basin under combined climate and LULC change scenarios. Integrating CMIP6 GCMs and Shared Socioeconomic Pathways (SSPs), projections indicate a 5-20% decrease in precipitation, with a more substantial decline, reaching up to 60%, anticipated in streamflow by the year 2100. Projections indicate that dry season flows will nearly cease, thereby confirming the "dry gets drier" paradigm. Furthermore, it is projected that the water yield will be increasingly concentrated along river corridors, with the majority of the basin experiencing an annual water volume of less than 129 mm by the end of the century. Projections indicate that the expansion of cropland will exceed 65% of the basin area, replacing wetlands and natural vegetation. Thirdly, to explore adaptation strategies, land suitability for drought-tolerant leguminous crops (sunn hemp and pigeon pea) was assessed in the Rundu sub-basins. This study proposed an innovative approach through the integration of subjective and objective analytical methods, which are independent of one another. The subjective component of the analysis employed a Multi-Criteria Decision Making-Analytic Hierarchy Process (MCDM-AHP), while the objective component used a data-driven multivariate approach supported by tree-based learning algorithms, including Random Forest and XGBoost. The MCDM-AHP method utilised expert evaluations to rank the importance of variables, identifying water sources, slope, and soil properties as key factors. A suitability mapping analysis revealed that 17.63% of the area was highly suitable and 62.77% moderately suitable for these legumes. Conversely, according to the data driven methodology, soil fertility and nitrogen content emerged as key determinants for land suitability. This integrated research underscores the sensitivity of streamflow to both precipitation and land cover dynamics in semi-arid regions and highlights the urgent need for nature-based adaptation strategies and an improved regulatory framework for climate resilient water management in the Okavango Basin. The findings aim to provide reference materials for water and land resource managers, policymakers, and concerned professionals to make informed decision and improve resource management and planning contributing in development of future adaptation strategies. Ultimately, this work contributes to a deeper understanding of the Okavango's hydrological system and its vulnerabilities, offering scientific evidence to support sustainable development, transboundary cooperation through entities like OKACOM, and alignment with SDGs in this critical basin.
Keywords: Okavango River
