Evaluation of an early flood warning system in Bamako (Mali): Lessons learned from the flood of May 2019

Abstract

Devastating floods have plagued many West African cities in the past decades. In an attempt to reduce flood damage in Bamako (Mali), an early warning system (EWS) demonstrator (Raincell App) was developed for flash floods. On 16 May 2019, while the demonstrator was partially operational, an intense rainfall event led to devastating floods. We carried out an experience feedback on this flood event by comparing EWS simulations to the results of a field survey. Given the synoptic situation and the rapid development pattern of the storm, none of the global forecasting systems were able to foresee its occurrence and magnitude. The hydrological model developed as part of the demonstrator correctly identified most of the locations where overbank flow occurred. In the absence of data, the predicted discharge and volume values could not be validated. However, they are realistic based on the water levels reported in the Post‐Disaster Needs Assessment report. It would be advisable to couple it to a two‐dimensional hydraulic model and add discharge and water level monitoring to the already existing rainfall surveillance scheme to further improve the system's performance. Increasing the local population's awareness of the dangers of clogged waterways is also mandatory.

Understanding the Regionality of Extreme Rainfall in the Sahel: The Mali Hotspot

“…Additionally, southwestern Mali (12°N -15°N) lies within the boreal summer southern storm track of AEW disturbances (Diehiou et al 1999;Fink and Reiner 2003;Cook 2005, 2008). AEW disturbances are conducive to MCS development over West Africa (Carlson 1969a,b;Reed et al 1977) and in some instances extreme rainfall events (Engel et al 2017;Fall et al 2020;Vizy and Cook 2022;Chahinian et al 2023) It is the relative permanence of these factors, with their influence on regional circulation and moisture transport, that favors extreme rainfall event development over southwestern Mali under the synoptic conditions discussed in this study (Fig. 2).…”

“…This morning event was associated with the development of an MCS in the prior afternoon ahead of an approaching AEW disturbance that slowed down as it approached the West African coast. Chahinian et al (2023) examined the 16 May 2019 heavy rainfall event over Bamako, Mali. A short-lived MCS formed in the early morning hours in association with a mid-level AEW disturbance in the northern storm track.…”

“…There has been a significant increase in their frequency (Chagnaud et al 2022;Saley and Salack 2023) as rainfall producing storms have become more intense and better organized (Taylor et al 2017;Tramblay et al 2020;Klien et al 2021). Flooding has increased as the storms become more frequent and destructive (Elagib et al 2021;Fofana et al 2022;Chahinian et al 2023), although some of the increase in flood disasters is associated with landuse/landcover changes associated with a quickly growing population (Sougué et al 2023). [Over the last 40 years, the population of the West African Sahel nations of Senegal, Gambia, Mauritania, Mali, Burkina Faso, and Niger has increased from around 27 million in 1979 to 92 million in 2021 (United Nations 2022)].…”

Detection of flooding by overflows of the drainage network: Application to the urban area of Dakar (Senegal)

“…The simplest methods, without introducing simulations of runoff formation, rely on the topographical characteristics of the territory to give a first local estimate of flood risk by accumulation of water at low points (Pons et al, 2010;Dehotin et al, 2015;Zheng et al, 2018). As for the 1D hydrological and hydraulic modeling approach, well established in the literature (Zhu et al, 2016;Rabori and Ghazavi, 2018;Sidek et al, 2021;Chahinian et al, 2023), it is applied to simulate stormwater drainage network performance (Meng et al, 2019;Pla et al, 2019). Modeling platforms such as SWMM (Rossman, 2015;Rabori and Ghazavi, 2018) or InfoWorks ICM are 1D simulation tools applied in urban environments (Rubinato et al, 2013;Sidek et al, 2021).…”

Preparing for severe flooding: Flood risk management research leading to better flood preparedness

“…Focus on structural and non‐structural flood mitigation approaches in research is also contributing towards increased flood resiliency and better flood preparedness for vulnerable communities around the world. In this issue, Chahinian et al (2023) evaluate the effectiveness of an early flood warning system with an examination into a 2019 flood event in Bamako, Mali. Other studies in this issue investigate the optimization of investments for reliability of various flood defence systems (Mooyaart et al, 2023) and asset management of flood defences and stakeholder cooperation (den Heijer, Podt, et al, 2023; den Heijer, Rijke, et al, 2023).…”