One of the main contributions of this project are the peer-review papers to be published by the members of AMMA-2050. This space will list published outputs from the project.
|Klein.Cornelia, Taylor, Christopher (2020) Dry soils can intensify mesoscale convective systems, PNAS, https://doi.org/10.1073/pnas.2007998117||Soil moisture plays a key role in the climate system by affecting rainfall and drought over land. Through its impact on temperature, humidity, and wind in the lower atmosphere, it can influence where thunderstorms initiate. However, in many regions of the world, traveling storm clusters known as mesoscale convective systems (MCSs) are the dominant source of rainfall, and very little is known about their response to surface conditions once triggered. We use satellite observations to demonstrate that dry soils at scales ≥200 km frequently create atmospheric conditions that intensify mature MCSs in the Sahel, long after their initiation. This surface-driven predictability of hazardous weather has potentially important applications, particularly in Africa, where the population is increasingly exposed to flood risk.|
|Largeron.Y, Guichard. F, Roehrig R, Couvreux F, Barbier J (2020) The April 2010 North African heatwave: when the water vapor greenhouse efect drives nighttime temperatures, Climate Dynamics https://doi.org/10.1007/s00382-020-05204-7||This study shows that the 2010 heatwave is characterized by strong positive anomalies of daily-minimum temperatures and the incoming longwave fuxes over North Africa by making use of several long-term observational datasets (satellite-based products and ground-stations, described in Sect. 2). It further explores the radiative impacts of clouds and aerosols on 2-m temperatures (Sects. 3 and 4) and shows that, although strong positive anomalies of AOD and cloud cover are found respectively over the Sahel and Sahara, their radiative impacts are too weak to explain the anomalies of longwave fuxes and temperatures.|
|Todzo S, Bichet A, Diedhiou A, (2020). Intensification of the hydrological cycle expected in West Africa over the 21st century. Earth System Dynamics,Earth Syst. Dynam.|
|To better understand the future impact of the warming on the hydrological cycle in the different subregions of West Africa, this study uses the state-of-the-art, high-resolution projections of the recent CORDEX-Africa (Giorgi et al., 2009; Jones et al., 2011; Hewitson et al., 2012; Kim et al., 2014) experiments to investigate, over the twenty-first century, the future changes in different aspects of the hydrological cycle and their relationship with regional temperatures. After describing the methodology (Sect. 2), the expected changes in temperature, precipitation, precipitation intensity, dry spells, wet spells, and HY-INT are identified (Sect. 3.1), before their relationship with regional temperature is quantified (Sect. 3.2). Section 4 discusses and concludes the study.|
|Sultan B, Lejeune Q, Menke I, Maskell G, Lee K, Noblet M..... Roudier P, (2020). Current needs for climate services in West Africa: Results from two stakeholder surveys. Climate Services. https://doi.org/10.1016/j.cliser.2020.100166||Climate services have been criticised in the past for their tendency to only disseminate results from climate research, rather than to seek to understand and tailor to the needs of their target audiences. Two surveys have been conducted within two projects, ISIpedia and CLIMAP, to assess users’ needs for climate and climate impacts information of all countries (with a foremost focus on West Africa) and for Senegal.|
|Fitzpatrick R, Parker D, Marsham J, Rowell D, Guichard F, Taylor C, Tucker S, (2020). What drives the intensification of mesoscale convective systems over the West African Sahel under Climate Change?. Journal of Climate, https://doi.org/10.1175/JCLI-D-19-0380.1||The purpose of this study is to understand the processes by which climate change can affect MCS precipitation rates, particularly the 99th percentile of surface precipitation rates from MCSs (hereafter termed the extreme precipitation rate), over the West African Sahel. We use a state-of-the-art regional climate model without any active convection parameterization scheme to understand how variability on the synoptic-to-climate time scale may affect MCS extreme precipitation rates.|
|Cornforth R, Parker D, Diop-Kane M, Fink A, Lafore J, Laing A..... Tompkins A, (2019). The First Forecasters’ Handbook for West Africa. Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-16-0273.1||The Forecasters’ Handbook builds upon the legacy of the African Monsoon Multidisciplinary Analysis (AMMA) project, making the latest science applicable to forecasting in the region. By bringing together, at the outset, researchers and forecasters from across the region, and linking to applications, user communities, and decision-makers, The Forecasters’ Handbook provides a template for finding much needed solutions to critical issues such as building resilience to weather hazards and climate change in West Africa.|
|Sow M, Diakhaté M, Dixon R, Guichard F, Dieng D, Gaye A, (2019). Uncertainties in the Annual Cycle of Rainfall Characteristics Over West Africa in CMIP5 Models. Atmosphere, DOI: 10.3390/atmos11020216||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.|
|Scannell C, Booth B, Dunstone N, Rowell D, Bernie D, Kasoar M, Paynter D, (2019). The Influence of Remote Aerosol Forcing from Industrialized Economies on the Future Evolution of East and West African Rainfall. Journal of Climate, 10.1175/JCLI-D-18-0716.1||Past changes in global industrial aerosol emissions have played a significant role in historical shifts in African rainfall, and yet assessment of the impact on African rainfall of near-term (10–40 yr) potential aerosol emission pathways remains largely unexplored. While existing literature links future aerosol declines to a northward shift of Sahel rainfall, existing climate projections rely on RCP scenarios that do not explore the range of air quality drivers. Here we present projections from two emission scenarios that better envelop the range of potential aerosol emissions.|
|Nkrumah F, Vischel T, Panthou G, Klutse N, Adukpo D, Diedhiou A, (2019). Recent Trends in the Daily Rainfall Regime in Southern West Africa. Atmosphere, https://doi.org/10.3390/atmos10120741||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).|
|Bichet A, Hingray B, Evin G, Diedhiou A, Kebe C, Anquetin S, (2019). Potential impact of climate change on solar resource in Africa for photovoltaic energy: analyses from CORDEX-AFRICA climate experiments. Environmental Research Letters, Volume 14, No.12||The development of renewable electricity in Africa could be massive in coming decades, as a response to the rapid rising electricity demand while complying with the Paris Agreements. This study shows that in the high-resolution climate experiments of CORDEX-AFRICA, the annual mean solar potential is expected to decrease on average by 4% over most of the continent by the end of the century, reaching up to 6% over the Horn of Africa, as a direct result of decrease in solar radiation and increase in air surface temperature.|
|Kouame Y, Obahoundje S, Diedhiou A, François B, Amoussou E, Anquetin S..... Yao E, (2019). Climate, Land Use and Land Cover Changes in the Bandama Basin (Côte D’Ivoire, West Africa) and Incidences on Hydropower Production of the Kossou Dam. Land. https://doi.org/10.3390/land8070103||Climate and land use/cover changes are potential drivers of change in hydrology and water use. Incidences of these factors on Bandama hydrological basin and Kossou hydropower generation (1981–2016) in West Africa are assessed in this present work.|
|Mortey E, Kouassi K, Diedhiou A, Anquetin S, Genoud M, Hingray B, Kouame D, (2019). Sustainable Hydroelectric Dam Management in the Context of Climate Change: Case of the Taabo Dam in Côte D’Ivoire, West Africa. Sustainability. https://doi.org/10.3390/su11184846||Management of hydroelectric dams is an aspect of sustainability that comes with resolving problems locally. The use of global indicators has not been a sustainable solution, thus the need for local indicators. Besides, current sustainability assessment tools lack the integration of climate, making assessments in a climate change context impossible. In this paper, we present management and sustainability assessment in a climate change context using sustainability indicators.|
|Finney D, Marsham J, Walker D, Birch C, Woodhams B, Jackson L, Hardy S, (2019). The effect of westerlies on East African rainfall and the associated role of tropical cyclones and the Madden–Julian Oscillation. RMetS. https://doi.org/10.1002/qj.3698||Variability of rainfall in East Africa has major impacts on lives and livelihoods. From floods to droughts, this variability is important on short daily time‐scales to longer decadal time‐scales, as is apparent from the devastating effects of droughts in East Africa over recent decades. Past studies have highlighted the Congo airmass in enhancing East African rainfall. Our detailed analysis of the feature shows that days with a westerly moisture flow, bringing the Congo airmass, enhance rainfall by up to 100% above the daily mean, depending on the time of year.|
|Sambou M, Janicot S, Pohl B, Badiane D, Dieng A, Gaye A, (2019). Heat wave occurrences over Senegal during spring: Regionalization and synoptic patterns. International Journal of Climatology, RMetS. https://doi.org/10.1002/joc.6220||The purpose of this paper is to investigate more in detail HW occurrences in spring over Senegal and their associated synoptic‐scale atmospheric pattern. In terms of meteorological characteristics, Senegal seems to be very specific and different from the rest of the Sahel.|
S. Berthou, E. J. Kendon,D. P. Rowell, M. J. Roberts, S. Tucker R. A. Stratton (2019) Larger Future Intensification of Rainfall in the West African Sahel in a Convection‐Permitting Model, Wiley, https://doi.org/10.1029/2019GL083544
|Monsoon rainfall in West Africa mostly comes from mesoscale convective systems, which are not well represented by standard convection‐parameterized regional climate models (RCMs). We use a 4.5 km resolution convection‐permitting RCM (CP4A) which has a good representation of these processes in the Sahel. By comparing the climate change signals of CP4A and a standard RCM (R25), we find that changes in mean rainfall and wet‐day frequency are linearly related. However, rainfall intensity changes are independent. Intensification of rainfall is larger in CP4A and happens in regions of both increasing and decreasing mean rainfall. Rainfall from extreme events increases by a factor of 5 to 10 in CP4A, compared to 2 to 3 in R25. CP4A also shows larger changes in intraseasonal rainfall variability, dry spells, and short and long duration extreme rainfall than R25, all of which are relevant for hydrology and agriculture.|
Ross.D.Dixon, Philippe Peyrillé, Françoise Guichard (2019)
Sahelian Precipitation Change Induced by SST Increase: The Contrasting Roles of Regional and Larger‐Scale Drivers, Wiley,
|Representing the West African Monsoon is a major challenge in climate modeling because of complex mechanisms of interaction across scales. We study the monsoon precipitation response to a 4K increase in sea surface temperatures using an idealized meridional‐vertical (2D) model, which allows separating regional‐ and larger‐scale influences. The 2D simulations reproduce key features of Atmospheric Model Intercomparison Project simulations and indicate that, in response to sea surface temperature increase, large‐scale changes induce a decrease of Sahel precipitation, while regional‐scale mechanisms generate a southward shift of the rainband. Large‐scale changes moisten and warm the free troposphere, while regional circulation changes increase low‐level moisture. Precipitation in the control simulations accounts for much of the variance in precipitation change for both Atmospheric Model Intercomparison Project and 2D simulations. This response is strongly connected to the large‐scale drivers of temperature and moisture, with an additional spread associated with the formulation of the convective parameterization.|
Benjamin Sultan, Dimitri Defrance ,Toshichika Iizumi (2019) Evidence of crop production losses in West Africa due to historical global warming in two crop models Springer Nature, https://doi.org/10.1038/s41598-019-49167-0
|Achieving food security goals in West Africa will depend on the capacity of the agricultural sector to feed the rapidly growing population and to moderate the adverse impacts of climate change. Indeed, a number of studies anticipate a reduction of the crop yield of the main staple food crops in the region in the coming decades due to global warming. Here, we found that crop production might have already been affected by climate change, with significant yield losses estimated in the historical past. We used a large ensemble of historical climate simulations derived from an atmospheric general circulation model and two process-based crop models, SARRA-H and CYGMA, to evaluate the effects of historical climate change on crop production in West Africa.|
Richard Lalou, Benjamin Sultan, Bertrand Muller & Alphousseyni Ndonky (2019) Does climate opportunity facilitate smallholder farmers’ adaptive capacity in the Sahel? Palgrove Communications. https://doi.org/10.1057/s41599-019-0288-8
In Africa, adaptation will be crucial to offset expected negative climate change impacts on food security and agriculture development. In this study, we combine meteorological data from 18 local stations, field surveys on agricultural practices and agronomic information on the growth of millet to demonstrate the crop suitability to the present climate and the ability of Senegalese farmers to adapt their practices to climate variability, and to disseminate them. From data collected in both 665 villages and 1061 farmers, our study provides quantitative evidence of the responsive adaptation of farmers in the Sahel where the recent resumption of rainfall has provided new agricultural opportunities. Statistical models and cropping simulations show that these farmers innovate by reintroducing and disseminating a long cycle millet cultivar—more suitable for wet environments.
Sonja Ayeb-Karlsson, Gino Fox, Dominic Kniveton (2019) Embracing uncertainty: A discursive approach to understanding pathways for climate adaptation in Senegal Springer, https://doi.org/10.1007/s10113-019-01495-7
|Climate change threatens to increase the frequency and intensity of droughts and floods. There are large uncertainties related to unknowns around the future and society’s responses to these threats. ‘Uncertainty’ as other words with the prefix ‘un’ (unknown, untold, unrest) often has negative connotations. Yet, uncertainty is manifested in virtually everything we do. To many in science, uncertainty is akin to error that should be minimised, a lack of knowledge that needs to be rectified. We argue that uncertainty rather should be embraced as a starting point for discussing pathways to climate adaptation. Here we follow a definition of ‘pathways to adaptation’ as representing a set of proactive changes in the present that move people from a climatically unsafe place, to positions of safety (self-defined as representing freedom from harm or adverse effect). This article applies an inter-discursive analytical approach where (un)certainty and (un)safety are used to deepen the understanding around the positions of people in Senegal, and their livelihoods, with respect to climate hazards. We examine the discursive socio-cultural values active in the climate adaptive space.|
Ségolène Berthou, David P. Rowell Elizabeth J. Kendon,
|The West African climate is unique and challenging to reproduce using standard resolution climate models as a large proportion of precipitation comes from organised deep convection. For the first time, a regional 4.5 km convection permitting simulation was performed on a pan-African domain for a period of 10 years (1997–2006). The 4.5 km simulation (CP4A) is compared with a 25 × 40 km convection-parameterised model (R25) over West Africa. CP4A shows increased mean precipitation, which results in improvements in the mature phase of the West African monsoon but deterioration in the early and late phases. The distribution of precipitation rates is improved due to more short lasting intense rainfall events linked with mesoscale convective systems. Consequently, the CP4A model shows a better representation of wet and dry spells both at the daily and sub-daily time-scales. The diurnal cycle of rainfall is improved, which impacts the diurnal cycle of monsoon winds and increases moisture convergence in the Sahel. Although shortcomings were identified, with implications for model development, this convection-permitting model provides a much more reliable precipitation distribution than its convection-parameterised counterpart at both daily and sub-daily time-scales. Convection-permitting scales will therefore be useful to address the crucial question of how the precipitation distribution will change in the future.|
Elizabeth.J.Kendon, Rachel A. Stratton, Simon Tucker, John H. Marsham, Ségolène Berthou, David P. Rowell & Catherine A. Senior (2019) Enhanced future changes in wet and dry extremes over Africa at convection-permitting scale Nature Communications https://doi.org/10.1038/s41467-019-09776-9
|African society is particularly vulnerable to climate change. The representation of convection in climate models has so far restricted our ability to accurately simulate African weather extremes, limiting climate change predictions. Here we show results from climate change experiments with a convection-permitting (4.5 km grid-spacing) model, for the first time over an Africa-wide domain (CP4A). The model realistically captures hourly rainfall characteristics, unlike coarser resolution models. CP4A shows greater future increases in extreme 3-hourly precipitation compared to a convection-parameterised 25 km model (R25). CP4A also shows future increases in dry spell length during the wet season over western and central Africa, weaker or not apparent in R25. These differences relate to the more realistic representation of convection in CP4A, and its response to increasing atmospheric moisture and stability. We conclude that, with the more accurate representation of convection, projected changes in both wet and dry extremes over Africa may be more severe.|
Zhang W, Brandt M, Penuelas J, Guichard F, Tong X, Tian F, Fensholt R, (2019). Ecosystem structural changes controlled by altered rainfall climatology in tropical savannas.. Nature communications, 10 (1), pp. 671
|Tropical savannas comprise mixed woodland grassland ecosystems in which trees and grasses compete for water resources thereby maintaining the spatial structuring of this ecosystem. A global change in rainfall climatology may impact the structure of tropical savanna ecosystems by favouring woody plants, relative to herbaceous vegetation. Here we analysed satellite data and observed a relatively higher increase in woody vegetation (5%) as compared to the increase in annual maximum leaf area index (LAImax, an indicator of the total green vegetation production) (3%) in arid and semi-arid savannas over recent decades. We further observed a declining sensitivity of LAImax to annual rainfall over 56% of the tropical savannas, spatially overlapping with areas of increased woody cover and altered rainfall climatology. This suggests a climate-induced shift in the coexistence of woody and herbaceous vegetation in savanna ecosystems, possibly caused by altered hydrological conditions with significance for land cover and associated biophysical effects such as surface albedo and evapotranspiration.|
|Julia Crook, Cornelia Klein, Sonja Folwell, Christoper M.Taylor, Douglas J.Parker, Rachel Stratton, Thorwald Stein (2019) Assessment of the Representation of West African Storm Lifecycles in Convection-Permitting Simulations AGU100 https://doi.org/10.1029/2018EA000491||Convection‐permitting models perform better at representing the diurnal cycle and the intermittency of convective rainfall over land than parameterized‐convection models. However, most of the previous model assessments have been from an Eulerian point of view, while key impacts of the rainfall depend on a storm‐relative perspective of the system lifecycle. Here a storm‐tracking algorithm is used to generate storm‐centered Lagrangian lifecycle statistics of precipitation over West Africa from regional climate model simulations and observations.|
|Concetta Burgarella Adeline Barnaud, Ndjido Ardo Kane, Frédérique Jankowski, Nora Scarcelli, Claire Billot, Yves Vigouroux, Cécile Berthouly-Salazar (2019) Adaptive Introgression An Untapped Evolutionary Mechanism for Crop Adaptation Front. Plant Sci https://doi.org/10.3389/fpls.2019.00004|
Global environmental changes strongly impact wild and domesticated species biology and their associated ecosystem services. For crops, global warming has led to significant changes in terms of phenology and/or yield. To respond to the agricultural challenges of this century, there is a strong need for harnessing the genetic variability of crops and adapting them to new conditions. Gene flow, from either the same species or a different species, may be an immediate primary source to widen genetic diversity and adaptions to various environments. When the incorporation of a foreign variant leads to an increase of the fitness of the recipient pool, it is referred to as “adaptive introgression”.
|Arona Diedhiou, Adeline Bichet, Richard Wartenburger, Sonia I Seneviratne, David P Rowell, Mouhamadou B Sylla,Ismaila Diallo, Stella Todzo, N'datchoh E Touré, Moctar Camara, Benjamin Ngounou Ngatchah, Ndjido A Kane, Laure Tall and François Affholder (2018) Changes in climate extremes over West and Central Africa at 1.5 °C and 2 °C global warming Environmental Research Letters, Volume 13, Number 6||In this study, we investigate changes in temperature and precipitation extremes over West and Central Africa (hereafter, WAF domain) as a function of global mean temperature with a focus on the implications of global warming of 1.5 °C and 2 °C according the Paris Agreement. We applied a scaling approach to capture changes in climate extremes with increase in global mean temperature in several subregions within the WAF domain: Western Sahel, Central Sahel, Eastern Sahel, Guinea Coast and Central Africa including Congo Basin.|
|M. Diakhaté, B. Rodríguez-Fonseca, I. Gómara, E. Mohino, A. L. Dieng, A. T. Gaye (2019) Oceanic Forcing on Interannual Variability of Sahel Heavy and Moderate Daily Rainfall AMS100 https://doi.org/10.1175/JHM-D-18-0035.1||This article analyzes SST remote forcing on the interannual variability of Sahel summer (June–September) moderate (below 75th percentile) and heavy (above 75th percentile) daily precipitation events during the period 1981–2016. Evidence is given that interannual variability of these events is markedly different. The occurrence of moderate daily rainfall events appears to be enhanced by positive SST anomalies over the tropical North Atlantic and Mediterranean, which act to increase low-level moisture advection toward the Sahel from the equatorial and north tropical Atlantic (the opposite holds for negative SSTs anomalies). In contrast, heavy and extreme daily rainfall events seem to be linked to El Niño–Southern Oscillation (ENSO) and Mediterranean variability.|
|The tendency of convective rainfall to initiate over a wetter or drier land surface is a critical feedback process in the climate system, influencing the hydrological cycle on a variety of spatial scales, especially in parts of the world where water is limited. A simple algebraic solution is derived from fundamental physical equations, to predict the sign of this convective rainfall feedback with the surface. The tendency for convection to occur is evaluated by the rate at which the convective boundary‐layer top approaches the level of free convection. Well‐known integral models predict the rate of ascent of the boundary‐layer top, which tends to be faster over a dry surface. The associated changes in equivalent potential temperature in the boundary layer determine the rate at which the level of free convection descends, typically faster over a wet surface, as a function of the ambient profile, the thermodynamic forcing and the surface Bowen ratio. The resulting system is controlled by three parameters. Two nondimensional parameters determine whether there is wet or dry “advantage”; the Bowen ratio at the boundary‐layer top and a “convective instability parameter,” defined as the ratio of the vertical gradient of saturated equivalent potential temperature at the level of free convection to the profile stability just above the boundary layer. A dimensional function, dependent on the surface fluxes, the boundary‐layer depth, and the profile stability, provides the magnitude of the response.|
Adama Bamba, Ismaila Diallo, N’Datchoh E. Touré, Kouakou Kouadio, Abdourahamane Konaré, Mamadou S. Dramé
|This modeling study is conducted to examine the potential impact of the reforestation (greenbelt) location (either in Sahel or in Guinean region) on West African summer climate system. To this end, three simulations using the regional climate model RegCM4 driven by ERA-Interim reanalysis were performed at 50 km horizontal resolution over a West African domain for the period 2000–2011. The first experiment, namely the control (CTRL), uses the standard vegetation cover, while the two others incorporate throughout the model integration, a zonal reforestation band of evergreen broadleaf over different locations: (i) over a 13° N–17° N band latitudes in a Sahel-Sahara region (experiment hereafter referred to as GB15N) and (ii) between 8.5° N–11.5° N in the Guinea Coast region (experiment hereafter referred to as GB10N).|
Marie-Jeanne G. Sambou, Serge Janicot, Benjamin Pohl, Daouda Badiane, Abdou Lahat Dieng, Amadou Gaye (2018)
Heat wave occurrences over Senegal during spring:
Regionalization and synoptic patterns https://doi.org/10.1002/joc.6220
|Based on 12 Senegalese stations of the Global Summary of the Day (GSOD) database (1979–2014), heat waves (HW) are defined for each station in spring (March–April–May, the hottest season in Senegal) as the daily maximum temperature (Tx), minimum temperature (Tn), or average apparent temperature of the day (AT), exceeding the corresponding 95% mobile percentile for at least three consecutive days. A hierarchical cluster analysis used to regionalize HW in these 12 stations is applied to simultaneous occurrences of daily temperature peaks over their 95% mobile percentiles. Three homogeneous zones of four stations each are identified (Zone 1, Zone 2 and Zone 3), from west (Atlantic coastline) to east (inland Senegal). Atmospheric circulation associated with HW is assessed through composites of ERA‐Interim deseasonalized anomalies, with the start date of each HW in each zone used as a reference.|
Mesoscale convective systems (MCSs) produce some of the most intense rainfall on the planet, and their response to climate variability and change is rather uncertain. Under global warming, increased water vapor is expected to intensify the most extreme rain events and enhance flood frequency. However, MCS dynamics are also sensitive to other atmospheric variables, most notably, wind shear. Here we build on a recent study showing strong MCS intensification in the African Sahel, and examine evidence of similar trends elsewhere in tropical Africa.
|G Panthou, T Lebel, T Vischel, G Quantin, Y Sane, A Ba, O Ndiaye, A Diongue-Niang and M Diopkane (2018) Rainfall intensification in tropical semi-arid regions: the Sahelian case IOP Publishing L https://iopscience.iop.org/article/10.1088/1748-9326/aac334/meta||An anticipated consequence of ongoing global warming is the intensification of the rainfall regimes meaning longer dry spells and heavier precipitation when it rains, with potentially high hydrological and socio-economic impacts. The semi-arid regions of the intertropical band, such as the Sahel, are facing particularly serious challenges in this respect since their population is strongly vulnerable to extreme climatic events. Detecting long term trends in the Sahelian rainfall regime is thus of great societal importance, while being scientifically challenging because datasets allowing for such detection studies are rare in this region. This study addresses this challenge by making use of a large set of daily rain gauge data covering the Sahel (defined in this study as extending from 20°W–10°E and from 11°N–18°N) since 1950, combined with an unparalleled 5 minute rainfall observations available since 1990 over the AMMA-CATCH Niger observatory.|
Fowe Tazen, Abdoulaye Diarra, Rodrigue F.W. Kabore Boubacar Ibrahim, Maïmouna Bologo/Traoré, Karim Traoré ,Harouna Karambiri (2018) 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 Wiley https://doi.org/10.1111/jfr3.12507
Urban areas in Sahelian West Africa are highly vulnerable to extreme hydro‐meteorological events. In recent years, Burkina Faso has experienced several natural disasters with floods being the most frequent. This study investigates flood trends in Ouagadougou and their relationship to extreme rainfall events. Fourteen rainfall indices were analysed to characterise the frequency and intensity of extreme rainfall. A frequency analysis of annual maximum daily rainfall series was performed using three statistical distributions.
|Catherine Wilcox, Théo Vischel, Gérémy Panthou, Ansoumana Bodian, Juliette Blanchet,Luc Descroix, Guillaume Quantin, Claire Cassé, Bachir Tanimoun, Soungalo Kone (2018) Trends in hydrological extremes in the Senegal & Niger Rivers ScienceDirect doi.org/10.1016/j.jhydrol.2018.07.063||In recent years, West Africa has witnessed an increasing number of damaging floods that raise the question of a possible intensification of the hydrological hazards in the region. In this study, the evolution of extreme floods is analyzed over the period 1950–2015 for seven tributaries in the Sudano-Guinean part of the Senegal River basin and four data sets in the Sahelian part of the Niger River basin.|
|Roberts, AJ, MJ Woodage, JH Marsham, EJ Highwood, CL Ryder, W McGinty, S Wilson and J Crook, (2018) Can explicit convection improve modelled dust in summertime West Africa? Atmos. Chem. Phys., 18, 9025-9048, 2018 doi.org/10.5194/acp-2017-1024, 2018||Global and regional models have large systematic errors in their modelled dust fields over West Africa. It is well established that cold-pool outflows from moist convection (haboobs) can raise over 50% of the dust over parts of the Sahara and Sahel in summer, but parameterised moist convection tends to give a very poor representation of this in models. Here, we test the hypothesis that an explicit representation of convection in the Met Office Unified Model (UM) improves haboob winds and so may reduce errors in modelled dust fields. .|
|Brahima Koné, Arona Diedhiou, N’datchoh Evelyne Touré, Mouhamadou Bamba Sylla, Filippo Giorgi, Sandrine Anquetin, Adama Bamba, Adama Diawara, and Arsene Toka Kobea (2018) Sensitivity study of the regional climate model RegCM4 to different convective schemes over West Africa Earth Syst. Dynam. doi.org/10.5194/esd-9-1261-2018||The latest version of RegCM4 with CLM4.5 as a land surface scheme was used to assess the performance and sensitivity of the simulated West African climate system to different convection schemes. The sensitivity studies were performed over the West African domain from November 2002 to December 2004 at a spatial resolution of 50 km × 50 km and involved five convective schemes: (i) Emanuel; (ii) Grell; (iii) Emanuel over land and Grell over ocean (Mix1); (iv) Grell over land and Emanuel over ocean (Mix2); and (v) Tiedtke. All simulations were forced with ERA-Interim data. Validation of surface temperature at 2 m and precipitation were conducted using data from the Climate Research Unit (CRU), Global Precipitation Climatology Project (GPCP) and the Tropical Rainfall Measurement Mission (TRMM) during June to September (rainy season), while the simulated atmospheric dynamic was compared to ERA-Interim data.|
|Adeline Bichet, Arona Diedhiou (2018) West African Sahel has become wetter during the last 30 years, but dry spells are shorter and more frequent Climate Research, doi.org/10.3354/cr01515||Over the twentieth century, Sahel rainfall has undergone extreme variations on a decadal timescale. This study investigated the recent precipitation changes in West African Sahel using a high-resolution Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) product over the period 1981-2014. We found that the recent increase in precipitation results principally from an increase in the number of wet days (+10 d compared to the normal) over the entire West African Sahel band, along with an increase in the precipitation intensity over the central part of the West African Sahel (+3 mm d-1). However, this overall increase in precipitation is associated with dry spells that are becoming more frequent but on average shorter over the entire West African Sahel band (on average by 30%), and with precipitation intensity that is decreasing (around 3 mm d-1 during the study period) in the western part of the West African Sahel (Senegal). Such reorganization (i.e. weaker but more frequent precipitation) is expected to be beneficial for agriculture and society, reducing the likelihood of both flooding and droughts.|
|Dagmawi Asfaw, Emily Black, Matthew Brown, Kathryn Jane Nicklin, Frederick Otu-Larbi, Ewan Pinnington, Andrew Challinor, Ross Maidment, and Tristan Quaife. (2018) TAMSAT-ALERT v1: a new framework for agricultural decision support. Geoscientific Model Development. https://doi.org/10.5194/gmd-11-2353-2018|
This paper presents a new operational framework to provide early warning of meteorological risk to agriculture. The framework is applied for the prediction of low maize yield in northern Ghana.
Adeline Bichet, Arona Diedhiou (2018) Less frequent and more intense rainfall along the coast of the Gulf of Guinea in West and Central Africa (1981–2014) Inter Research Science Publisher. doi.org/10.3354/cr01537
|Since the 1990s, rainfall has been reported to increase over the Gulf of Guinea. In light of the devastating floods that have occurred since the 1990s over the coastal areas of this region, this work aims to better characterize the recent trends in precipitation for this region. We used the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) product, a new observational rainfall dataset that covers the period 1981-2014 at high resolution and daily time steps. During the first rainy season (April-June), we find that the lack of significant trend observed in mean precipitation hides a trend towards less frequent but more intense rainfall along the coast of the Gulf of Guinea, which is expected to increase the likelihood of flooding and droughts, and fits with the recent increase in devastating floods. Over the north however (between 7° and 12.5°N), rainfall has become more frequent and less intense, which is expected to decrease the likelihood of flooding and droughts. During the second rainy season (September-November), we find that the clear increase in mean precipitation observed between 5° and 12.5°N results from an increase in precipitation intensity and frequency, while over southern Cameroon, the decrease in mean precipitation hides a trend towards less frequent but more intense rainfall. In both seasons, the average duration of wet spells has greatly decreased along the coast, in favor of more numerous and more intense isolated wet days.|
|Klein, Cornelia; Belušić, Danijel; Taylor, Christopher M.. 2018 Wavelet scale analysis of mesoscale convective systems for detecting deep convection from infrared imagery. Journal of Geophysical Research: Atmospheres. https://doi.org/10.1002/2017JD027432||Focusing on West Africa, we show that Meteosat cloud top temperatures are a useful proxy for rainfall intensities, as derived from snapshots from the Tropical Rainfall Measuring Mission 2A25 product: MCSs larger than 15,000 km2 at a temperature threshold of −40°C are found to produce 91% of all extreme rainfall occurrences in the study region, with 80% of the storms producing extreme rain when their minimum temperature drops below −80°C. We present a new method based on 2‐D continuous wavelet transform to explore the relationship between cloud top temperature and rainfall intensity for subcloud features at different length scales.|
|Salomon Obahoundje, Arona Diedhiou,Eric Antwi Ofosu ,Sandrine Anquetin,Baptiste François,Julien Adounkpe,Ernest Amoussou,Yao Morton Kouame,Kouakou Lazare Kouassi,Vami Hermann Nguessan Bi and Marc Youan Ta (2018) Assessment of Spatio-Temporal Changes of Land Use and Land Cover over South-Western African Basins and Their Relations with Variations of Discharges Hydrology. doi.org/10.3390/hydrology5040056||West African basins play a vital role in the socio-economic development of the region. They are mostly trans-boundary and sources of different land use practices. This work attempts to assess the spatio-temporal land use and land cover changes over three South Western African basins (Volta, Mono and Sassandra basins) and their influence on discharge. The land use and land cover maps of each basin were developed for 1988, 2002 and 2016. The results show that all the studied basins present an increase in water bodies, built-up, agricultural land and a decline in vegetative areas. These increases in water bodies and land use are as a result of an increase in small reservoirs, of dugouts and of dam constructions. However, the decline in some vegetative clusters could be attributed to the demographic and socio-economic growth as expressed by the expansion of agriculture and urbanization. The basic statistical analysis of precipitation and discharge data reveals that the mean annual discharge varies much more than the total annual precipitation at the three basins. We showed that this great variation in discharge is mainly due to land use and land cover changes. Beside the hydrological modification of the land use and land cover changes, the climate of the region as well as the water quality and availability and the hydropower generation may be impacted by these changes in land surfaces conditions. Therefore, these impacts should be further assessed to implement appropriate climate services and measures for a sustainable land use and water management.|
|Lala Kounta, Xavier Capet, Julien Jouanno, Nicolas Kolodziejczyk4, Bamol Sow,and Amadou Thierno Gaye (2018) A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic – Part 1: the poleward slope currents along West Africa Ocean Science doi.org/10.5194/os-14-971-2018||The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic.|
(Editors) Douglas J. Parker, Mariane Diop‐Kane (2017) Meteorology of Tropical West Africa: The Forecasters’ Handbook Wiley DOI:10.1002/9781118391297
|Meteorology of tropical West Africa: the Forecasters’ Handbook presents the science and practice of weather forecasting for an important region of the tropics. Connecting basic theory with forecasting practice, the book provides a unique training volume for operational weather forecasters, and is also suitable for students of tropical meteorology.|
Aymeric Ricome, François Affholder, Françoise Gérard, Bertrand Muller, Charlotte Poeydebat, Philippe Quirion, Moussa Sall. Are subsidies to weather-index insurance the best use of public funds? A bio-economic farm model applied to the Senegalese groundnut basin. Elsevier http://dx.doi.org/10.1016/j.agsy.2017.05.015
|While crop yields in Sub-Saharan Africa are low compared to most other parts of the world, weather-index insurance is often presented as a promising tool, which could help resource-poor farmers in developing countries to invest and adopt yield-enhancing technologies. Here, we test this hypothesis on two contrasting areas (in terms of rainfall scarcity) of the Senegalese groundnut basin through the use of a bio-economic farm model, coupling the crop growth model CELSIUS with the economic model ANDERS, both specifically designed for this purpose.|
E.T.N’Datchoh, I.Diallo, A.Konaré, S.Silué, K.O.Ogunjobi, A,Diedhieou and M.Doumbia Dust induced changes on the West African summer monsoon feature. Royal Meteorological Society http://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/joc.5187
|Dust generation and transportation from North Africa are thought to modulate the West African Monsson (WAM) features. In this study, we investigated the relationship between the Saharan Air Layer located above Atlantic Ocean (OSAL) and WAM features, including Monsoon flow, African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ) over West Africa using the RegCM4 regional model at 30km grid resolution.|
Famien, A. M., Janicot, S., Ochou, A. D., Vrac, M., Defrance, D., Sultan, B., and Noël, T.: A bias-corrected CMIP5 dataset for Africa using the CDF-t method – a contribution to agricultural impact studies, Earth Syst. Dynam., 9, 313-338, https://doi.org/10.5194/esd-9-313-2018, 2018.
This paper aims to present a new dataset of bias-corrected CMIP5 global climate model (GCM) daily data over Africa. This dataset was obtained using the cumulative distribution function transform (CDF-t) method, a method that has been applied to several regions and contexts but never to Africa… Evaluation of the results over West Africa has been carried out on a list of priority user-based metrics that were discussed and selected with stakeholders. It includes simulated yield using a crop model simulating maize growth.
|Sane, Y., Panthou, G., Bodian, A., Vischel, T., Lebel, T., Dacosta, H., Quantin, G., Wilcox, C., Ndiaye, O., Diongue-Niang, A., and Diop Kane, M.: Intensity-Duration-Frequency (IDF) rainfall curves in Senegal, Nat. Hazards Earth Syst. Sci. Discuss., https://doi.org/10.5194/nhess-2017-352, in review, 2017.||This study confirms previous works showing that simple scaling holds for characterizing the time-space structure of extreme rainfall in tropical regions such as sub-Saharan Africa. It further provides confidence intervals for the parameter estimates, and shows that the uncertainty linked to the estimation of the GEV parameters, is 3 to 4 times larger than the uncertainty linked to the inference of the scaling parameter.|
Juliette Blanchet, Claire Aly, Théo Vischel, Gérémy Panthou, Youssouph Sané, Mariane Diop Kane (2018), Trend in the Co‐Occurrence of Extreme Daily Rainfall in West Africa Since 1950.
In this paper we propose a statistical framework to study the evolution of the co-occurrence of extreme daily rainfall in West Africa since 1950. Two regions are considered, subject to contrasted rainfall regimes: Senegal and the central Sahel.The paper discusses how the co-occurrence of extremes can provide a qualitative indicator on change in size and propagation of the strongest storms.
|Lafore, J.-P., Beucher, F., Peyrillé, P., Diongue-Niang, A., Chapelon, N., Bouniol, D., Caniaux, G., Favot, F., Ferry, F., Guichard, F., Poan, E., Roehrig, R. and Vischel, T. (2017), A multi-scale analysis of the extreme rain event of Ouagadougou in 2009. Q.J.R. Meteorol. Soc., 143: 3094–3109. doi:10.1002/qj.3165||This study presents a multi-scale analysis of an extreme rain event that occurred in Burkina Faso on 1 September 2009 (263 mm rainfall observed at Ouagadougou). This high-impact weather system results from the combination of several favourable ingredients at different scales. This study suggests that this extreme rainfall event results from the combination of several favourable ingredients arising at different scales such as SST patterns, equatorial waves including MJO, Kelvin, ER, MRG and an AEW train, as well as a pre-existing large-scale wet spell. Further studies are necessary to confirm the relative importance of these ingredients and of their combination based on other case-studies of extreme events and on statistical studies.|
W. Zhang, M. Brandt, F. Guichard, Q. Tian, R. Fensholt (2017) Using long-term daily satellite based rainfall data (1983–2015) to analyze spatio-temporal changes in the sahelian rainfall regime Journal of Hydrology http://dx.doi.org/10.1016/j.jhydrol.2017.05.033
The sahelian rainfall regime is characterized by a strong spatial as well as intra- and inter-annual variability. Here we analyse rainfall regime variables that require daily observations: onset, cessation, and length of the wet season; seasonal rainfall amount; number of rainy days; intensity and frequency of rainfall events; number, length, and cumulative duration of dry spells.
Using 17 years (1998–2014) of daily TRMM 3B42 rainfall data, we provide a climatological characterization of wet and dry spells in West Africa, which should serve to assess the ability of climate model to simulate these high impact events. The study focuses on four sub-regions (Western and Central Sahel, Sudanian zone and Guinea Coast).
K.L. Sheen, D.M. Smith, N.J. Dunstone, R. Eade, D.P. Rowell & M. Vellinga (2017) Skilful prediction of Sahel summer rainfall on inter-annual and multi-year timescales Nature Communications DOI: 10.1038/ncomms14966
Summer rainfall in the Sahel region of Africa exhibits one of the largest signals of climatic variability and with a population reliant on agricultural productivity, the Sahel is particularly vulnerable to major droughts such as occurred in the 1970s and 1980s. Rainfall levels have subsequently recovered, but future projections remain uncertain. Here we show that Sahel rainfall is skilfully predicted on inter-annual and multi-year (that is, 5 years) timescales and use these predictions to better understand the driving mechanisms.
C.M. Taylor, D. Belušić, FGuichard, D. J. Parker, T. Vischel, O. Bock, P.P. Harris, S. Janicot, C. Klein & Gérémy Panthou (2017) Frequency of extreme Sahelian storms tripled since 1982 in satellite observations Nature 544, 475–478 doi:10.1038/nature22069
This study reveals global warming is responsible for a tripling in the frequency of extreme West African Sahel storms observed in just the last 35 years. The study, which has analysed trends from 35 years of satellite observations across Africa, provides unique insight into how some of the most violent storms in the world are responding to rising global temperatures. The research indicates that MCS intensification is linked to increasingly hot conditions in the Sahara desert resulting from man-made greenhouse gas emissions.
A. J. Hartley, D.J. Parker, L. Garcia-Carreras, S. Webster (2016) Simulation of vegetation feedbacks on local and regional scale precipitation in West Africa Agricultural and Forest Meteorology http://dx.doi.org/10.1016/j.agrformet.2016.03.001
Planned changes to land use in West Africa have been proposed to both combat desertification and to preserve biodiversity in the region, however, there is an urgent need for tools to assess the effects of these proposed changes on local and regional scale precipitation. We use a high-resolution, convection-permitting numerical weather prediction (NWP) model to study how the initiation and propagation of mesoscale convective systems (MCS) depends on the surface vegetation cover.
B. Sultan and M. Gaetani (2016): Agriculture in West Africa in the Twenty-first Century: climate change and impacts scenarios, and potential for adaptation, Crop Science and Horticulture, http://dx.doi.org/10.3389/fpls.2016.01262
This review paper provides a comprehensive overview of climate change impacts on agriculture in West Africa based on the recent scientific literature.
P. Good, B. B.B. Booth, R. Chadwick, E. Hawkins, A. Jonko & J. A. Lowe (2016) Large differences in regional precipitation change between a first and second 2 K of global warming Nature Communications DOI: 10.1038/ncomms13667
For adaptation and mitigation planning, stakeholders need reliable information about regional precipitation changes under different emissions scenarios and for different time periods. A significant amount of current planning effort assumes that each K of global warming produces roughly the same regional climate change. Here using 25 climate models, we compare precipitation responses with three 2 K intervals of global ensemble mean warming.
K. Guan, B. Sultan, M. Biasutti, C. Baron, D.B. Lobell (2016): Assessing climate adaptation options and uncertainties for cereal systems in West Africa, Agricultural and Forest Meteorology, http://dx.doi.org/10.1016/j.agrformet.2016.07.021
In the coming decades, the fragile agricultural system in West Africa will face further challenges in meeting food security, both from increasing population and climate change. Optimal prioritization of adaptation investments requires the assessment of possible adaptation options and their uncertainties. We adopt a new assessment framework to account for the impacts of proposed adaptation options in the historical climate and their ability to reduce the impacts of future climate change.
A. J. Challinor, A.-K. Koehler, J. Ramirez-Villegas, S. Whitfield and B. Das (2016): Current warming will reduce yields unless maize breeding and seed systems adapt immediately, Nature Climate Change, doi:10.1038/nclimate3061
Crop yields will fall within the next decade due to climate change unless immediate action is taken to speed up the introduction of new and improved varieties, experts have warned. The research, led by the University of Leeds and published in the journal Nature Climate Change, focusses on maize in Africa but the underlying processes affect crops across the tropics. The CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) funded the study. This research was partly funded by the NERC/DFID Future Climate For Africa programme.