West Africa Extreme Rainfall Events and Large-Scale Ocean Surface and Atmospheric Conditions in the Tropical Atlantic

Ta, Samuel; Kouadio, Yves K.; Ali, Kasim; Toualy, Elisée; Aman, Angora; Yoroba, Fidèle

doi:10.1155/2016/1940456

Cited by 39 publications

(36 citation statements)

References 42 publications

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“…The local percentiles were used to select the intense events at a daily timescale, in accordance with other studies carried out at continental or sub-continental scale [39][40][41]. Along the coast, mean annual precipitation shows a large range of values, from less than 900 mm at Lomé (Togo) to over 2000 mm at Axim (Ghana) and Tabou (Ivory Coast).…”

Section: Definition Of Intense Rainfall Eventsmentioning

confidence: 99%

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

2020

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Daily rainfall in southern West Africa (4-8 • N, 7 • W-3 • E) is analyzed with the aim of documenting the intense rainfall events which occur in coastal Ivory Coast, Ghana, Togo, and Benin. The daily 99th percentile (P99) shows that the coastline experiences higher intensity rainfall than inland areas. Using Tropical Rainfall Measuring Mission (TRMM) rainfall data for 1998-2014, a novel way of classifying the intense events is proposed. We consider their space-time structure over a window of 8 • latitude-longitude and five days centered on the event. A total 39,680 events (62 at each location) are classified into three major types, mainly found over the oceanic regions south of 5 • N, the Bight of Benin, and the inland regions respectively. These types display quite distinct rainfall patterns, propagation features, and seasonal occurrence. Three inland subtypes are also defined. The atmospheric circulation anomalies associated with each type are examined from ERA-interim reanalysis data. Intense rainfall events over the continent are mainly a result of westward propagating disturbances. Over the Gulf of Guinea, many intense events occur as a combination of atmospheric disturbances propagating westward (mid-tropospheric easterly waves or cyclonic vortices) and eastward (lower tropospheric zonal wind and moisture anomalies hypothesized to reflect Kelvin waves). Along the coast, there is a mixture of different types of rainfall events, often associated with interacting eastward-and westward-moving disturbances, which complicates the monitoring of heavy precipitation.

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Section: Definition Of Intense Rainfall Eventsmentioning

confidence: 99%

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

2020

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“…Evidence of climate change in Nigeria has been discussed by [16], who reported increasing damage caused by wind and rainstorms, which are projected to increase in southern regions [17]. The northern part of the country has been experiencing a reduction in rainfall and an increase in the rates of dryness and heat [18,19], while the rainfall amounts have been increasing in the southern part with an irregular pattern [19,20]. Moreover, climate projections for the 21st century show a significant increase of temperature over all the ecological zones [17] which may have negative 2 Advances in Meteorology impacts on agriculture and food security.…”

Section: Introductionmentioning

confidence: 99%

Geospatial Analysis of Extreme Weather Events in Nigeria (1985–2015) Using Self-Organizing Maps

Akande

Costa

Mateu

et al. 2017

Advances in Meteorology

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The explosion of data in the information age has provided an opportunity to explore the possibility of characterizing the climate patterns using data mining techniques. Nigeria has a unique tropical climate with two precipitation regimes: low precipitation in the north leading to aridity and desertification and high precipitation in parts of the southwest and southeast leading to large scale flooding. In this research, four indices have been used to characterize the intensity, frequency, and amount of rainfall over Nigeria. A type of Artificial Neural Network called the self-organizing map has been used to reduce the multiplicity of dimensions and produce four unique zones characterizing extreme precipitation conditions in Nigeria. This approach allowed for the assessment of spatial and temporal patterns in extreme precipitation in the last three decades. Precipitation properties in each cluster are discussed. The cluster closest to the Atlantic has high values of precipitation intensity, frequency, and duration, whereas the cluster closest to the Sahara Desert has low values. A significant increasing trend has been observed in the frequency of rainy days at the center of the northern region of Nigeria.

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“…Precisely, an important feature also observed in VIMF anomaly patterns from July to October is the westward intense anomalies over WA extending over the equatorial Atlantic Ocean. For extreme rainfall events in WA, Ta et al [100] found the contrary; VIMF is dominant to the east and it penetrates into WA mainly from the equatorial Atlantic Ocean.…”

Section: Roles Of the Sources During Extremely Dry Conditionsmentioning

confidence: 94%

On the Connection between Atmospheric Moisture Transport and Dry Conditions in Rainfall Climatological Zones of the Niger River Basin

Sorí

Nieto

Drumond

et al. 2019

Water

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The hydroclimatology of the Niger River basin, located in West Africa, is very complex. It has been widely studied because of its importance to the socioeconomic activities of the countries that share its natural resources. In this study, to better understand the causes and mechanisms that modulate the rainfall over the Niger River basin, we identified the most relevant moisture sources for precipitation within the basin. The Lagrangian model FLEXPART was utilised to track backward trajectories of air parcels initially losing humidity over climatological rainfall zones of the basin. Along 10-day backward trajectories, we computed the budget of the difference between evaporation and precipitation (E − P) from 1000 to 0.1 hPa, permitting the identification of those regions where moisture uptake ((E − P) > 0) prevail. The study was conducted for the period 1980–2017. Monthly maps of ((E − P) > 0 were developed to illustrate the regions from where moisture is transported, contributing to precipitation in the Niger River basin. The spatial variability of the sources matches the precipitation variability over the basin restricted to surrounding areas of the Niger River basin during months with low average precipitation and widely spreading over the continent and the Atlantic Ocean in months with high average precipitation. During climatological dry months (e.g., December, January and February) the continental sources of West and Northeast Africa and the climatological rainfall zones themselves provide most of the moisture for precipitation. However, during the rainy season, the moisture supplies from oceanic sources increase, becoming greater than the contribution from land-based sources during August (the rainiest month). Dry conditions were identified for each climatological rainfall zone using the Standardised Precipitation Index. Similar to many previous studies, we found that the 1980s were highlighted by dry conditions. Local recycling and particularly moisture uptake from the tropical South Atlantic Ocean seem to be highly related to dry and wet conditions in the basin. A reduction on the moisture uptake from surrounding continental sources and the tropical South Atlantic Ocean is almost persistent during extremely dry conditions. Ascending movements are restricted to the lower troposphere during extremely dry conditions and oscillate latitudinally as well as precipitation.

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West Africa Extreme Rainfall Events and Large-Scale Ocean Surface and Atmospheric Conditions in the Tropical Atlantic

Cited by 39 publications

References 42 publications

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

Geospatial Analysis of Extreme Weather Events in Nigeria (1985–2015) Using Self-Organizing Maps

On the Connection between Atmospheric Moisture Transport and Dry Conditions in Rainfall Climatological Zones of the Niger River Basin

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