Abstract
In the last decades, the Sahelian area was hit by an increase of flood events, both in frequency and in magnitude. In order to prevent damages, an early warning system (EWS) has been planned for the Sirba River, the major tributary of the Middle Niger River Basin. The EWS uses the prior notification of Global Flood Awareness System (GloFAS) to realize adaptive measures in the exposed villages. This study analyzed the performances of GloFAS 1.0 and 2.0 at Garbey Kourou. The model verification was performed using continuous and categorical indices computed according to the historical flow series and the flow hazard thresholds. The unsatisfactory reliability of the original forecasts suggested the performing of an optimization to improve the model performances. Therefore, datasets were divided into two periods, 5 years for training and 5 years for validation, and an optimization was conducted applying a linear regression throughout the homogeneous periods of the wet season. The results show that the optimization improved the performances of GloFAS 1.0 and decreased the forecast deficit of GloFAS 2.0. Moreover, it highlighted the fundamental role played by the hazard thresholds in the model evaluation. The optimized GloFAS 2.0 demonstrated performance acceptable in order to be applied in an EWS.
Highlights
The last decades have been characterized by a drastic global increase in magnitude and frequency of flood events [1,2]
This study focused on the Sirba River, one of the major tributaries of the Middle Niger River
The results jointly considered the four forecasted series (5 days Global Flood Awareness System (GloFAS) 1.0 and 2.0 both in original and optimized format) and compared them with the observed flow series
Summary
The last decades have been characterized by a drastic global increase in magnitude and frequency of flood events [1,2]. The Sahelian area has recorded a strong rain inter-annual variability and an increase in magnitude and frequency of extreme rainfall events [4,5], coupled with an increase in flood occurrences [6,7]. The anomaly, called the “Sahel Paradox”, is that the streamflow in Sahelian rivers is higher compared to those from 1950 to 1960 [9,10]. The reason for the higher streamflow is heavily debated in the research community and cannot be entirely explained by a single factor [11,12]. The hydrological changes may be caused by the increment of the extreme rainfall events [13], the changes in land use and land cover [14,15,16], and the rupture of the endorheic basins [17,18,19]
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