Abstract
Flooding is a growing concern in West Africa. Improved quantification of discharge extremes and associated uncertainties is needed to improve infrastructure design, and operational forecasting is needed to provide timely warnings. In this study, we use discharge observations, a hydrological model (Niger-HYPE) and extreme value analysis to estimate peak river flow statistics (e.g. the discharge magnitude with a 100-year return period) across the Niger River basin. To test the model's capacity of predicting peak flows, we compared 30-year maximum discharge and peak flow statistics derived from the model vs. derived from nine observation stations. The results indicate that the model simulates peak discharge reasonably well (on average + 20%). However, the peak flow statistics have a large uncertainty range, which ought to be considered in infrastructure design. We then applied the methodology to derive basin-wide maps of peak flow statistics and their associated uncertainty. The results indicate that the method is applicable across the hydrologically active part of the river basin, and that the uncertainty varies substantially depending on location. Subsequently, we used the most recent bias-corrected climate projections to analyze potential changes in peak flow statistics in a changed climate. The results are generally ambiguous, with consistent changes only in very few areas. To test the forecasting capacity, we ran Niger-HYPE with a combination of meteorological data sets for the 2008 high-flow season and compared with observations. The results indicate reasonable forecasting capacity (on average 17% deviation), but additional years should also be evaluated. We finish by presenting a strategy and pilot project which will develop an operational flood monitoring and forecasting system based in-situ data, earth observations, modelling, and extreme statistics. In this way we aim to build capacity to ultimately improve resilience toward floods, protecting lives and infrastructure in the region.
Highlights
The Niger River is West Africa's largest river, with more than 100 million inhabitants within the 2.1 Â 106 km2 catchment area
Provided peak observations are adequate, utilizing the Niger-HYPE outputs for infrastructure design would typically provide an additional level of caution toward the risk of floods
Similar results were obtained for all investigated peak flow statistics
Summary
The Niger River is West Africa's largest river, with more than 100 million inhabitants within the 2.1 Â 106 km catchment area. The river basin extends into nine countries and spans several climate regions, from humid tropical to desert (Fig. 1). Floods are a growing concern taking lives and damaging infrastructure; and resulting in personal tragedies, substantial repair costs and disruption of transportation (Fig. 2). Increasing flooding in recent years (e.g. in 2008 and 2016) can partly be attributed to climate variability and to land use changes (Aich et al, 2015). The region has been designated as a sensitive area for potential future climate change (Diallo et al, 2016). Better understanding of potential peak flows could contribute to improved infrastructure design, and operational flood forecasts could facilitate emergency response and thereby increase societal resilience to future floods in the region
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