scholarly journals Trend in the Co‐Occurrence of Extreme Daily Rainfall in West Africa Since 1950

2018 ◽  
Vol 123 (3) ◽  
pp. 1536-1551 ◽  
Author(s):  
Juliette Blanchet ◽  
Claire Aly ◽  
Théo Vischel ◽  
Gérémy Panthou ◽  
Youssouph Sané ◽  
...  
Keyword(s):  
West Africa ◽  
Daily Rainfall

scholarly journals Uncertainties in the Annual Cycle of Rainfall Characteristics over West Africa in CMIP5 Models

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 216
Author(s):  
Magatte Sow ◽  
Moussa Diakhaté ◽  
Ross D. Dixon ◽  
Françoise Guichard ◽  
Diarra Dieng ◽  
...  
Keyword(s):  
West Africa ◽  
Annual Cycle ◽  
Late Onset ◽  
Daily Rainfall ◽  
Cmip5 Models ◽  
Monthly Precipitation ◽  
Strongly Coupled ◽  
Precipitation Estimates ◽  
Latitudinal Position ◽  
Systematic Biases

We analyse uncertainties associated with the main features of the annual cycle of West African rainfall (amplitude, timing, duration) in 15 CMIP5 simulations over the Sahelian and Guinean regions with satellite daily precipitation estimates. The annual cycle of indices based on daily rainfall such as the frequency and the intensity of wet days, the consecutive dry (CDD) and wet (CWD) days, the 95th percentile of daily rainfall (R95), have been assessed. Over both regions, satellite datasets provide more consistent results on the annual cycle of monthly precipitation than on higher-frequency rainfall indices, especially over the Guinean region. By contrast, CMIP5 simulations display much higher uncertainties in both the mean precipitation climatology and higher-frequency indices. Over both regions, most of them overestimate the frequency of wet days. Over the Guinean region, the difficulty of models to represent the bimodality of the annual cycle of precipitation involves systematic biases in the frequency of wet days. Likewise, we found strong uncertainties in the simulation of the CWD and the CDD over both areas. Finally, models generally provide too early (late) onset dates over the Sahel (the Guinean region) and overestimate rainfall during the early and late monsoon phases. These errors are strongly coupled with errors in the latitudinal position of the ITCZ and do not compensate at the annual scale or when considering West Africa as a whole.

scholarly journals Interactions between Convection and a Moist Vortex Associated with an Extreme Rainfall Event over Southern West Africa

2019 ◽  
Vol 147 (7) ◽  
pp. 2309-2328 ◽  
Author(s):  
Marlon Maranan ◽  
Andreas H. Fink ◽  
Peter Knippertz ◽  
Sabastine D. Francis ◽  
Aristide B. Akpo ◽  
...  
Keyword(s):  
West Africa ◽  
Extreme Values ◽  
Vortex Formation ◽  
Daily Rainfall ◽  
Extreme Rainfall ◽  
Squall Line ◽  
Convective System ◽  
Extreme Rainfall Event ◽  
Guinea Coast ◽  
Free Atmosphere

Abstract An intense mesoscale convective system (MCS) in the Guinea Coast region caused one of the highest ever recorded daily rainfall amounts at the Nigerian station Abakaliki on 12 June 2016 (223.5 mm). This paper provides a detailed analysis of the meso- and synoptic-scale factors leading to this event, including some so far undocumented dynamical aspects for southern West Africa. The MCS formed over the Darfur Mountains due to diurnal heating, then moved southwestward along a mid- to lower-tropospheric trough, and developed into a classical West African squall line in a highly sheared environment with pronounced midlevel dryness. Strong moisture flux convergence over Nigeria prior to the MCS passage led to extreme values in precipitable water and was caused by the formation of a local, short-lived heat low. According to the pressure tendency equation, the latter resulted from tropospheric warming due to MCS-forced subsidence as well as surface insolation in the resulting almost cloud-free atmosphere. In this extremely moist environment, the MCS strongly intensified and initiated the formation of a lower-tropospheric vortex, which resulted in a deceleration of the MCS and high rainfall accumulation at Abakaliki. Following the vorticity equation, the vortex formation was realized through strong low-level vortex stretching and upper-level vertical vorticity advection related to the MCS, which became “dynamically large” compared to the Rossby radius of deformation. Eventually, moisture supply and lifting associated with the vortex are suggested to promote the longevity of the MCS during the subsequent westward movement along the Guinea Coast.

scholarly journals Recent Trends in the Daily Rainfall Regime in Southern West Africa

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 741 ◽  
Author(s):  
Francis Nkrumah ◽  
Théo Vischel ◽  
Geremy Panthou ◽  
Nana Ama Browne Klutse ◽  
David C. Adukpo ◽  
...  
Keyword(s):  
West Africa ◽  
Rainy Season ◽  
Daily Rainfall ◽  
Annual Rainfall ◽  
Large Set ◽  
Mean Intensity ◽  
Mean Annual Rainfall ◽  
Recent Trends ◽  
The Mean ◽  
Climate Events

Extreme climate events, either being linked to dry spells or extreme precipitation, are of major concern in Africa, a region in which the economy and population are highly vulnerable to climate hazards. However, recent trends in climate events are not often documented in this poorly surveyed continent. This study makes use of a large set of daily rain gauge data covering Southern West Africa (extending from 10° W to 10° E and from 4° N to 12° N) from 1950 to 2014. The evolution of the number and the intensity of daily rainfall events, especially the most extremes, were analyzed at the annual and seasonal scales. During the first rainy season (April–July), mean annual rainfall is observed to have a minor trend due to less frequent but more intense rainfall mainly along the coast of Southern West Africa (SWA) over the last two decades. The north–south seasonal changes exhibit an increase in mean annual rainfall over the last decade during the second rainy season (September–November) linked by both an increase in the frequency of occurrence of rainy days as well as an increase in the mean intensity and extreme events over the last decade. The study also provides evidence of a disparity that exists between the west and east of SWA, with the east recording a stronger increase in the mean intensity of wet days and extreme rainfall during the second rainy season (September–November).

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

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 188
Author(s):  
Pierre Camberlin ◽  
Marc Kpanou ◽  
Pascal Roucou
Keyword(s):  
West Africa ◽  
Atmospheric Circulation ◽  
Daily Rainfall ◽  
Tropical Rainfall Measuring Mission ◽  
Heavy Precipitation ◽  
Reanalysis Data ◽  
Intense Rainfall ◽  
Rainfall Events ◽  
Easterly Waves ◽  
Atmospheric Circulation Anomalies

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.

scholarly journals Uncertainties in the Annual Cycle of Rainfall Characteristics over West Africa in CMIP5 Models

2019 ◽  
Author(s):  
Magatte Sow ◽  
Moussa Diakhaté ◽  
Françoise Guichard ◽  
Diarra Dieng ◽  
Amadou T. Gaye
Keyword(s):  
West Africa ◽  
Annual Cycle ◽  
Late Onset ◽  
Coupled Model ◽  
Daily Rainfall ◽  
Cmip5 Models ◽  
Rainfall Characteristics ◽  
Intercomparison Project ◽  
The Mean ◽  
Annual Scale

This study analyses uncertainties associated with the annual cycle of West African rainfall characteristics in 15 simulations of the Coupled Model Intercomparison Project phase 5 (CMIP5) over the Sahel and Guinean regions. Indices based on daily rainfall such as the frequency and the ntensity of wet days, the consecutive dry days (CDD) and wet days (CWD), the 95th percentile of daily rainfall (R95) and its contribution to the umulative monsoon rainfall (R95PTOT) have been assessed. Over both regions, TRMM, GPCP and CHIRPS observational datasets provide very consistent results on the annual cycle of precipitation but less so on the frequency of wet days. Conversely, higher uncertainties are noted on the intensity of wet days over both study areas, particularly over the Guinean region. Overall, CMIP5 simulations present much higher uncertainties in the representation of the mean precipitation climatology, often provide too early (late) onset dates over the Sahel (the Guinean region) and overestimate rainfall during the early and late monsoon phases. These errors do not compensate at the annual scale nor when considering West Africa as a hole. Results also reveal that over the Guinean region, the difficulty of models to represent the annual structure of the mean precipitation strongly involves biases in the representation of the annual cycle of the frequency of wet days. We found strong uncertainties in the simulation of the CWD and he CDD over both areas. Conversely for R95p and R95PTOT, the ncertainties in CMIP5 models appear somewhat weaker, but the magnitude f R95 is largely underestimated in most models.

scholarly journals Uncertainties in the Annual Cycle of Rainfall Characteristics Over West Africa in CMIP5 Models

2019 ◽  
Author(s):  
Magatte Sow ◽  
Moussa Diakhaté ◽  
Ross D. Dixon ◽  
Françoise Guichard ◽  
Diarra Dieng ◽  
...  
Keyword(s):  
West Africa ◽  
Annual Cycle ◽  
Late Onset ◽  
Daily Rainfall ◽  
Cmip5 Models ◽  
Monthly Precipitation ◽  
Strongly Coupled ◽  
Precipitation Estimates ◽  
Latitudinal Position ◽  
Systematic Biases

This study analyses uncertainties associated with the main features of the annual cycle of West African rainfall (amplitude, timing, duration) in 15 CMIP5 simulations over the Sahelian and Guinean regions with satellite daily precipitation estimates. The annual cycle of indices based on daily rainfall such as the frequency and the intensity of wet days, the consecutive dry (CDD) and wet days (CWD), the 95th percentile of daily rainfall (R95) have been assessed. Over both regions, satellite datasets provide more consistent results on the annual cycle of monthly precipitation than on higher-frequency rainfall indices, especially over the Guinean region. CMIP5 simulations display much higher uncertainties in both the mean precipitation climatology and higher-frequency indices. Over both regions, most of them overestimate the frequency of wet days. Over the Guinean region, the difficulty of models to represent the bimodality of the annual cycle of precipitation involves systematic biases the frequency of wet days. Likewise, we found strong uncertainties in the simulation of the CWD and the CDD over both areas. Finally, models generally provide too early (late) onset dates over the Sahel (the Guinean region) and overestimate rainfall during the early and late monsoon phases. These errors are strongly coupled errors in the latitudinal position of the ITCZ and do not compensate at the annual scale nor when considering West Africa as a whole. wet days. We found strong uncertainties in the simulation of the CWD and he CDD over both areas. Conversely for R95p and R95PTOT, the ncertainties in CMIP5 models appear somewhat weaker, but the magnitude f R95 is largely underestimated in most models.

scholarly journals How a typical West African day in the future-climate compares with current-climate conditions in a convection-permitting and parameterised convection climate model

2020 ◽  
Vol 163 (1) ◽  
pp. 267-296
Author(s):  
Rory G. J. Fitzpatrick ◽  
Douglas J. Parker ◽  
John H. Marsham ◽  
David P. Rowell ◽  
Lawrence S. Jackson ◽  
...  
Keyword(s):  
West Africa ◽  
Climate Model ◽  
Coupled Model ◽  
Daily Rainfall ◽  
Future Climate ◽  
Decision Makers ◽  
Precipitation Event ◽  
Climate Conditions ◽  
Current Climate ◽  
The Future

AbstractCurrent-climate precipitation and temperature extremes have been identified by decision makers in West Africa as among the more impactful weather events causing lasting socioeconomic damage. In this article, we use a plausible future-climate scenario (RCP8.5) for the end of the twenty-first century to explore the relative commonness of such extremes under global warming. The analysis presented considers what a typical day in the future climate will feel like relative to current extrema. Across much of West Africa, we see that the typical future-climate day has maximum and minimum temperatures greater than 99.5% of currently experienced values. This finding exists for most months but is particularly pronounced during the Boreal spring and summer. The typical future precipitation event has a daily rainfall rate greater than 95% of current storms. These findings exist in both a future scenario model run with and without parameterised convection, and for many of the Coupled Model Inter-comparison Project version 5 ensemble members. Additionally, agronomic monsoon onset is projected to occur later and have greater inter-annual variability in the future. Our findings suggest far more extreme conditions in future climate over West Africa. The projected changes in temperature and precipitation could have serious socioeconomic implications, stressing the need for effective mitigation given the potential lack of adaptation pathways available to decision makers.

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