Trends in flood events and their relationship to extreme rainfall in an urban area of Sahelian West Africa: The case study of Ouagadougou, Burkina Faso

Fowé, Tazen; Diarra, Abdoulaye; Kabore, Rodrigue F.W.; Ibrahim, Boubacar; Bologo, Maïmouna; Traoré,; Traoré, Karim; Karambiri, Harouna

doi:10.1111/jfr3.12507

Cited by 58 publications

(45 citation statements)

References 34 publications

(43 reference statements)

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“…However, the nature of intraseasonal rainfall variability has changed over the Sahel during recent decades, with an observed increase in the frequency of very rainy MCSs separated by longer periods of little to no rainfall (Panthou et al 2014;Taylor et al 2017). More intense rain events carry increased risk of flooding, with observational studies suggesting that flood events over the Sahel have become more frequent over the past decades (Panthou et al 2014;Nka et al 2015;Panthou et al 2018;Tazan et al 2019;Wilcox et al 2018). Intense but temporarily sparse rain events can also deteriorate soil quality through nutrient runoff (Panagos et al 2017).…”

Section: Introductionmentioning

confidence: 99%

What Drives the Intensification of Mesoscale Convective Systems over the West African Sahel under Climate Change?

et al. 2020

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Extreme rainfall is expected to increase under climate change, carrying potential socioeconomic risks. However, the magnitude of increase is uncertain. Over recent decades, extreme storms over the West African Sahel have increased in frequency, with increased vertical wind shear shown to be a cause. Drier midlevels, stronger cold pools, and increased storm organization have also been observed. Global models do not capture the potential effects of lower- to midtropospheric wind shear or cold pools on storm organization since they parameterize convection. Here we use the first convection-permitting simulations of African climate change to understand how changes in thermodynamics and storm dynamics affect future extreme Sahelian rainfall. The model, which simulates warming associated with representative concentration pathway 8.5 (RCP8.5) until the end of the twenty-first century, projects a 28% increase of the extreme rain rate of MCSs. The Sahel moisture change on average follows Clausius–Clapeyron scaling, but has regional heterogeneity. Rain rates scale with the product of time-of-storm total column water (TCW) and in-storm vertical velocity. Additionally, prestorm wind shear and convective available potential energy both modulate in-storm vertical velocity. Although wind shear affects cloud-top temperatures within our model, it has no direct correlation with precipitation rates. In our model, projected future increase in TCW is the primary explanation for increased rain rates. Finally, although colder cold pools are modeled in the future climate, we see no significant change in near-surface winds, highlighting avenues for future research on convection-permitting modeling of storm dynamics.

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Section: Introductionmentioning

confidence: 99%

What Drives the Intensification of Mesoscale Convective Systems over the West African Sahel under Climate Change?

et al. 2020

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“…The potential decrease in the number of rainy days and the consecutive wet days call for investment in water harvesting initiatives to ensure water availability for domestic and agricultural use during the dry periods. The potential for more heavy and intense precipitation events poses a risk to infrastructure over the study domain, which is vulnerable to floods [70,71].…”

Section: Discussionmentioning

confidence: 99%

Intraseasonal Precipitation Variability over West Africa under 1.5 °C and 2.0 °C Global Warming Scenarios: Results from CORDEX RCMs

Ogega

Gyampoh

Mistry

2020

Climate

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This study assessed the performance of 24 simulations, from five regional climate models (RCMs) participating in the Coordinated Regional Climate Downscaling Experiment (CORDEX), in representing spatiotemporal characteristics of precipitation over West Africa, compared to observations. The top five performing RCM simulations were used to assess future precipitation changes over West Africa, under 1.5 °C and 2.0 °C global warming levels (GWLs), following the representative concentration pathway (RCP) 8.5. The performance evaluation and future change assessment were done using a set of seven ‘descriptors’ of West African precipitation namely the simple precipitation intensity index (SDII), the consecutive wet days (CWD), the number of wet days index (R1MM), the number of wet days with moderate and heavy intensity precipitation (R10MM and R30MM, respectively), and annual and June to September daily mean precipitation (ANN and JJAS, respectively). The performance assessment and future change outlook were done for the CORDEX–Africa subdomains of north West Africa (WA-N), south West Africa (WA-S), and a combination of the two subdomains. While the performance of RCM runs was descriptor- and subregion- specific, five model runs emerged as top performers in representing precipitation characteristics over both WA-N and WA-S. The five model runs are CCLM4 forced by ICHEC-EC-EARTH (r12i1p1), RCA4 forced by CCCma-CanESM2 (r1i1p1), RACMO22T forced by MOHC-HadGEM2-ES (r1i1p1), and the ensemble means of simulations made by CCLM4 and RACMO22T. All precipitation descriptors recorded a reduction under the two warming levels, except the SDII which recorded an increase. Unlike the WA-N that showed less frequency and more intense precipitation, the WA-S showed increased frequency and intensity. Given the potential impact that these projected changes may have on West Africa’s socioeconomic activities, adjustments in investment may be required to take advantage of (and enhance system resilience against damage that may result from) the potential changes in precipitation.

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“…On the one hand they bring the majority of rainfall required for agriculture (e.g., Laurent et al 1998;Laing et al 1999;Lafore et al 2011), but on the other hand, the most intense events can bring severe urban flooding (e.g., Engel et al 2017;Lafore et al 2017), damage to crops (e.g., Lobell and Gourdji 2012), and enhanced erosion (Panagos et al 2017). Panthou et al (2014) and Taylor et al (2017) have found a substantial recent increase in the frequency of these severe events, with other studies showing a corresponding increase in flood frequency (Nka et al 2015;Tazan et al 2019;Wilcox et al 2018). Globally, the frequency of intense rainfall events is expected to continue to increase as climate warms in response to rising anthropogenic carbon emissions (e.g., Kharin et al 2013;Kendon et al 2019), but at regional scales, the specific risks-measured for example by a ''defensible plausible range''-are largely unknown.…”

Section: Introductionmentioning

confidence: 99%

Understanding Intermodel Variability in Future Projections of a Sahelian Storm Proxy and Southern Saharan Warming

et al. 2021

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Projected changes in the intensity of severe rain events over the North African Sahel – falling from large mesoscale convective systems – cannot be directly assessed from global climate models due their inadequate resolution and parameterization of convection. Instead, the large-scale atmospheric drivers of these storms must be analyzed. Here we study changes in meridional lower tropospheric temperature gradient across the Sahel (ΔTGrad), which affect storm development via zonal vertical wind shear and Saharan air layer characteristics. Projected changes in ΔTGrad vary substantially amongst models, adversely affecting planning decisions that need to be resilient to adverse risks, such as increased flooding. This study seeks to understand the causes of these projection uncertainties and finds three key drivers. The first is inter-model variability in remote warming, which has strongest impact on the East Sahel, decaying towards the West. Second – and most important – a warming-advection-circulation feedback in a narrow band along the South Sahara varies in strength between models. Third, variations in South Saharan evaporative anomalies weakly affect ΔTGrad, although for an outlier model these are sufficiently substantive to reduce warming here to below that of the global mean. Together these uncertain mechanisms lead to uncertain South Saharan / North Sahelian warming, causing the bulk of large inter-model variations in ΔTGrad. In the South Sahel, a local negative feedback limits the contribution to uncertainties in ΔTGrad. This new knowledge of ΔTGrad projection uncertainties provides understanding that can be used, in combination with further research, to constrain projections of severe Sahelian storm activity.

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Trends in flood events and their relationship to extreme rainfall in an urban area of Sahelian West Africa: The case study of Ouagadougou, Burkina Faso

Cited by 58 publications

References 34 publications

What Drives the Intensification of Mesoscale Convective Systems over the West African Sahel under Climate Change?

What Drives the Intensification of Mesoscale Convective Systems over the West African Sahel under Climate Change?

Intraseasonal Precipitation Variability over West Africa under 1.5 °C and 2.0 °C Global Warming Scenarios: Results from CORDEX RCMs

Understanding Intermodel Variability in Future Projections of a Sahelian Storm Proxy and Southern Saharan Warming

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