Hydrological functioning of inland valleys for water management in the Sudanian zones of Benin
(2025)
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- Inland valleys are critical hydrological systems for agricultural resilience in Sub-Saharan Africa, but their sustainable water management is hampered by data scarcity and a fragmented knowledge of their hydrological functioning. This research aimed to assess the governing hydrological mechanisms within these systems in order to inform operational frameworks for sustainable water resource management and support context-specific decision-making. For this purpose, an integrated methodological approach was applied, combining systematic literature review, field observations, statistical analyses, hydrological modeling, and the joint use of in situ measurements and remote sensing data. The work focused on five inland valleys located in Northern and Central Benin (Itchedjiro, Lower-Sowé, Bahounkpo, Nalohou, and Ara). More specifically, the study (1) analyzed dominant hydrological processes and their drivers across different spatial and temporal scales, (2) evaluated the reliability of alternative hydro-climatic data sources for water dynamic assessment in the inland valleys and (3) tested the applicability of the GR4J hydrological model integrated with satellite data for decision support in water resource management. Hydrological responses across the studied inland valleys exhibited variability, reflecting diverse functional behaviors that challenge oversimplified assumptions. Runoff patterns spanned from rapid-flow events to more buffered regimes, shaped by a combination of factors including rainfall characteristics (intensity and volume), soil texture (notably clay and sand contents), watershed area, and land use-land cover (particularly forest cover). The influence of these factors varied according to the temporal resolution of analysis, ranging from individual rainfall events to daily, annual, and multiyear scales. The topographic position relative to the flow axis emerged as a determinant of groundwater dynamics, with specific relationships identified between rainfall, and groundwater behavior along each toposequence. The comparative analysis of in-situ and satellite-based climatic data revealed limitations and biases in commonly used satellite rainfall products in West Africa (GPM-IMERG, GSMaP, CHIRPS, PERSIANN-CDR, ERA5). Results showed spatio-temporal variability in the reliability of these products and poor performance for intense rainfall events (> 50 mm/day). Although GSMaP and GPM-IMERG showed better statistical agreement with daily measured rainfall, CHIRPS emerged as the most coherent and useful source for hydrological analysis on the study sites due to its relative spatio-temporal stability. Rainfall estimates from ERA5 and PERSIANN-CDR were found to be poorly suited. Regarding reference evapotranspiration, temperature-based methods (e.g., Hargreaves), fed with ERA5 temperature estimates (reliable for the study area), performed well and offered a pragmatic alternative to more data-intensive methods such as the FAO-56 Penman-Monteith. The GR4J model demonstrated a satisfactory ability to simulate runoff dynamics at the outlets of the studied inland valleys but showed limitations in representing low flows and extreme flood peaks. Site-specific reliability was observed for simulations driven by satellite rainfall data. CHIRPS provided the best representation of discharge dynamics at Bahounkpo and Lower-Sowé, while GPM-IMERG performed well at Nalohou. The integration of the GR4J model with satellite rainfall data enabled long-term hydrological reconstructions, revealing a trend of increasing runoff and providing quantitative estimates of extreme flood frequencies, important for updating the engineering design guidelines and informing agricultural planning. The approach developed in this study provides an insightful foundation for improving water management in inland valleys, even in poorly gauged contexts. It confirms that ground-based hydro-climatic monitoring remains essential for accurately understanding processes and for calibrating decision-support models. This approach enables water balance assessments, which are essential for climate-resilient agriculture, informed planning, and operational decision-making by engineers, policymakers, and agricultural support services in data-scarce inland valleys. For ungauged areas, a pragmatic pathway is proposed for the operational assessment of the water balance. By identifying physical controls and demonstrating the operational value of tested tools, this work supports a necessary shift toward more informed and sustainable water management strategies in African inland valley ecosystems.
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Tidjani, A. (2025). Hydrological functioning of inland valleys for water management in the Sudanian zones of Benin. https://hdl.handle.net/2078.5/259692