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This work concerns the rainy season delay in Western of Africa toward Dakar area in the country of Senegal. Since 2006, continuous dry air intrusions from Western Sahara have been recorded in the lower layers at the beginning of the monsoon season from Western Sahara. This dust by indirect effect tends to inhibit convective systems. Here, we present one among several cases where convection was inhibited by dry air intrusions near the coastlines in 2012 between 23 and 24 July in Dakar, Senegal. Meanwhile, Tambacounda (East of Senegal) recorded 75 mm of rainfall, unlike Dakar where there has been only traces of rain. For these days, the convective activity monitoring is carried from ORL data and METEOSAT images. The in situ data, such as radiosondes and lidar pictures, clearly show that the dry air is located in the low layers between 200 and 400 m. The AERONET data confirm that this dry layer is composed of dust with 2.2 microns of size. HYPLIT-4 back-trajectory model and NCAR/NCEP reanalysis indicate that the dry air in Dakar area is from Western Sahara (Morocco). They also show subsiding movements, accompanied by a strong North wind and a weak Easterly wind during these 2 days in Dakar. The results of this study clearly show that the dry air tends to slow down the Eastern movements of waves and inhibit some convective cells like those of July 23–24.

Backgrond: The Sahelian zone of Senegal is marked by heatwave events due to temperatures increase especially in 2013 exceeding 45 ° C with an impact on morbidity and mortality rise. In order to document health impacts of recurrent extreme temperatures in this part of the country, a study was carried out combining heatwaves detection, occurrence of climate-sensitive diseases and risk factors for exposure.Methods: To do this, a set of climatic (temperatures) and health (morbidity, mortality) data were collected for April, May and June season from 2009 to 2019. These data were complemented by surveys on exposure risk factors of 1246 households. Statistical methods were used to carry out univariate and bivariate analyzes while cartographic techniques allowed visualization of the main climatic and health indicators.Results: The results show an increase in temperatures compared to seasonal normal for the 1971-2000 reference period with threshold exceedances of the 90th percentiles (42°C) for the maxima and (27°C) the minima and higher temperatures during the months of May and June. From health perspective, it was noted an increase in cases of consultation on health facilities as well as a rise in declared morbidity by households especially in the departments of Kanel (17.7%), Ranérou (16.1 %), Matam (13.7%) and Bakel (13.7%). The heatwaves of May 2013 were also associated with cases of death with a reported mortality (observed by medical staff) of 12.4% unevenly distributed according to the departments with a higher number of deaths in Matam (25, 2%) and in Bakel (23.5%) than in Podor (8.4%) and Kanel (0.8%). The morbidity and mortality distribution according to gender shows that women (57%) were more affected than men (43%). These health risks have been associated with a number of factors including age, access to drinkable water, type of fuel, type of housing and construction materials, existence of fan, an air conditioner, health antecedents, etc.Conclusion: The heatwaves recurrence has led to an upsurge in certain diseases sensitive to rising temperatures, which is increasingly a public health issue in the Sahelian zone of Senegal.

The Sahelian zone of Senegal experienced heat waves in the previous decades, such as 2013, 2016 and 2018 that were characterised by temperatures exceeding 45°C for up to 3 successive days. The health impacts of these heat waves are not yet analysed in Senegal although their negative effects have been shown in many countries. This study analyses the health impacts of observed extreme temperatures in the Sahelian zone of the country, focusing on morbidity and mortality by combining data from station observation, climate model projections, and household survey to investigate heat wave detection, occurrence of climate-sensitive diseases and risk factors for exposure. To do this, a set of climatic (temperatures) and health (morbidity, mortality) data were collected for the months of April, May and June from 2009 to 2019. These data have been completed with 1246 households' surveys on risk factor exposure. Statistical methods were used to carry out univariate and bivariate analyses while cartographic techniques allowed mapping of the main climatic and health indicators. The results show an increase in temperatures compared to seasonal normal for the 1971-2000 reference period with threshold exceedances of the 90th percentiles (42°C) for the maxima and (27°C) the minima and higher temperatures during the months of May and June. From health perspective, it was noted an increase in cases of consultation in health facilities as well as a rise in declared morbidity by households especially in the departments of Kanel (17.7%), Ranérou (16.1 %), Matam (13.7%) and Bakel (13.7%). The heat waves of May 2013 were also associated with cases of death with a reported mortality (observed by medical staff) of 12.4% unequally distributed according to the departments with a higher number of deaths in Matam (25, 2%) and in Bakel (23.5%) than in Podor (8.4%) and Kanel (0.8%). The morbidity and mortality distribution according to gender shows that women (57%) were more affected than men (43%). These health risks have been associated with a number of factors including age, access to drinkable water, type of fuel, type of housing and construction materials, existence of fan and an air conditioner, and health history.The heat wave recurrence has led to a frequency in certain diseases sensitive to rising temperatures, which is increasingly a public health issue in the Sahelian zone of Senegal.

Backgrond: The Sahelian zone of Senegal is marked by heatwave events due to temperatures increase especially in 2013 exceeding 45 ° C with an impact on morbidity and mortality rise. In order to document health impacts of recurrent extreme temperatures in this part of the country, a study was carried out combining heatwaves detection, occurrence of climate-sensitive diseases and risk factors for exposure. Methods To do this, a set of climatic (temperatures) and health (morbidity, mortality) data were collected for April, May and June season from 2009 to 2019. These data were complemented by surveys on exposure risk factors of 1246 households. Statistical methods were used to carry out univariate and bivariate analyzes while cartographic techniques allowed visualization of the main climatic and health indicators. Results The results show an increase in temperatures compared to seasonal normal for the 1971-2000 reference period with threshold exceedances of the 90th percentiles (42°C) for the maxima and (27°C) the minima and higher temperatures during the months of May and June. From health perspective, it was noted an increase in cases of consultation on health facilities as well as a rise in declared morbidity by households especially in the departments of Kanel (17.7%), Ranérou (16.1%), Matam (13.7%) and Bakel (13.7%). The heatwaves of May 2013 were also associated with cases of death with a reported mortality (observed by medical staff) of 12.4% unevenly distributed according to the departments with a higher number of deaths in Matam (25, 2%) and in Bakel (23.5%) than in Podor (8.4%) and Kanel (0.8%). The morbidity and mortality distribution according to gender shows that women (57%) were more affected than men (43%). These health risks have been associated with a number of factors including age, access to drinkable water, type of fuel, type of housing and construction materials, existence of fan, an air conditioner, health antecedents, etc. Conclusion The heatwaves recurrence has led to an upsurge in certain diseases sensitive to rising temperatures, which is increasingly a public health issue in the Sahelian zone of Senegal.

Observed rainfall data of the National Meteorological Service of Guinea (NMS) exhibit that synoptic station usually records the largest rainfall amount in Guinea. Only few studies have been done on this rainfall peak observed in Conakry. This work better analyses the atmospheric dynamics leading to rainfall particularity. Using NMS data from 1981 to 2010, the monthly contribution and mean seasonal cycle of each station has been done. These findings of the study show that between July and August (rainfall season peak), the coastline particularly Conakry records the largest amount of rainfall. Using Era Interim data for the common period (1981-2010), we also investigate the rainfall dynamics in the lower level (1000 hPa - 850 hPa) from precipitable water, divergence, and moisture flow transport. There is a west and southwest moisture flow transport explained by a strong moisture convergence in the coastal region (Lower-Guinea). Furthermore, values of precipitable water in the same region are found, in agreement with the high moisture flow transport gradient. These incoming flow (west and south-west) undergo a return by blocking’s Kakoulima range (foehn effect) and Fouta Djallon massif to initiate convection clouds on the Guinean coast. These processes enhance a convergence of moisture associated with orographic origin convection. This has an important effect by increasing the rainfall amount in Conakry.

Bush fires are increasingly becoming a threat to Guinean ecosystems and their understanding is a big challenge to scientists and environmental managers. Using the FARSITE model (Fire Area Simulator), this paper presents the prediction of the spread and characteristics of bush fires in the savannahs of North-eastern Guinea, specifically in Malea/Siguiri prefecture. Inputs, vegetation and topography dataset from satellite imagery (30 m resolution, Landsat and SRTM respectively) as well as in-situ meteorological data (wind, temperature and humidity) were used. These data obtained from the boundaries of the area of study were prepared using Geographic Information System (GIS). The burning time and the ignition points were fixed while admitting 3 scenarios: spread of fire in a plain without wind; spread on hills without wind effect and spread with wind effect. The results show that, in these savannahs, the intensity of the fire lines can reach 4133,3 KW/m under the effect of winds. Without winds, a decrease of 69% over plains and 68% over hills is noted. The amount of heat released could go up to 38000 KJ/m2 with the wind effect. While, without the wind effect a decrease of 10 and 9% over the plains and hills is observed respectively. Eventually, the speed of propagation reaches 8 m/min (0.5 km/h), but without the wind, it would decrease up to 73 and 61% over plains and hills, respectively. This study could be improved to serve as a decision support tool for the management of ecosystems North-eastern Guinea. Key words: Fire area, prediction modeling, simulator, ecosystem managers, Guinea.

Following the high temperatures recorded in the Sahel during 2010 and most recently in May 2013 in the northern part of Senegal where the temperature oscillated between 45 and 50 degrees, significant human deaths were recorded. A good understanding of the dynamics of these heat waves thus become necessary not only to improve the prediction of these events, but also to better assess the impact of future climate change on the occurrence and intensification of these heat waves. To address this issue, simulated CMIP5 daily bias-corrected temperature data interpolated on a 0.5° grid over 1950-2099 have been used by focusing on 3 RCP (Representative Concentration Pathways) scenarios, RCP8.5, RCP4.5 and RCP2.6 . The heat waves in Senegal are defined by relying on exceeding of a moving percentile relative to maximum, minimum and mean temperature during 3 consecutive days over the MAM (March-April-May), the hottest season of the year. Senegal is characterized by a steep zonal temperature gradient from the coast to hinterland. In RCP8.5, the general temperature increase present for the last 60 years (+1.5°C) will continue and reach ~ +5°C in 2100. In this context, at the end of the century the mean temperatures of the western coastal zone will be similar to the present ones of the eastern continental zone, and the warmest spring seasons recorded over the last 15 years will be the norm around 2040. Then exceptional and yet unknown intense heat waves are planned and policy and decision makers will have to anticipate reliable adaptation strategies.

International audience

Monthly means of boundary layer height (BLH) over West Africa are presented based on 36 years (1979-2014) of six-hourly ERA-Interim reanalysis. In this region, we found that there is a link between the West Africa Monsoon (WAM) and the monthly means of BLH in the summer. The trend and empirical orthogonal function (EOF) of BLH are presented, including the mid July variability of BLH with the precipitation. The dominant EOF of BLH accounts for around 42% of the variance with slightly large amplitude in the north while relatively small in the equatorial band. The second EOF which accounts for 16.4%, describes a longitudinal contrast with a zonal gradient. The relationship between BLH and precipitation is found using the canonical correlation analysis (CCA). Significant trends of the first and second pairs of BLH with precipitation are shown. The first and second CCA pair has a correlation of 68% and 60% with 12.2 and 10.8 degrees of freedom respectively. The critical correlation coefficients at the 95% level are 0.21 and 0.65 for the first and second CCA pairs respectively. This first CCA pair mostly determines the arid and semi-arid areas where the rate of explained regional variance is about 78% in the arid area and 73% in the semi-arid area. For the second pair of CCA, the rate of explained regional variance is more than 60% in the Guinea coast and wet equatorial area.

This study investigates the variability and the predictability of bush fire on inter-annual and multi-year timescales in Guinea (latitudes 7° 05 and 12° 51 N and longitudes 7° 30 and 15° 10 W). Using Moderate Resolution Imaging Spectroradiometer (MODIS) with a spatial resolution of 231 m × 231 m and 16 days composite temporal resolution between 2001 and 2016, two brush fire hazard indices are calculated based on the NDVI variability. Results show that both indices could be considered as good indicators of NDVI deficiency corresponding to the drought of vegetation. Multiple linear regression model using these risk indices as predictors and burned areas as predictands has shown a non-significant model skill of 0.33 (lower than the significant threshold equals to 0.42), at the inter-annual scale, while at the multi-year timescale (>5 years), the model’s skill rise up to 0.89. These indices can therefore be used as predictors of Guinea burned areas on multi-year timescale. This novel finding improved our understanding on the forecasting of burned area in Guinea, and could therefore help for successful adaptation strategies. Key words: Bush fire, Guinea, index of risk, NDVI-MODIS, variability and predictability.

18 pages; International audience; 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. The main pattern controlling the presence of HW in Senegal consists in positive pressure anomalies centred around the strait of Gibraltar, promoting easterly to northeasterly wind anomalies. This causes higher temperatures in the three zones of Senegal, and lower temperatures and drier air over the central Sahel. This pattern is opposite to that characteristic of HW in the central Sahel shown in previous studies. From Zone 1 to Zone 3, the temperature and moisture patterns are shifted to the east while pressure anomalies weaken drastically. Night‐time Tn‐HW are characterized by higher water vapour contents than daytime Tx‐HW, corroborating and complementing previous studies over the Sahel. These HW patterns are close to the canonical mode of intra‐seasonal atmospheric variability over Senegal.

Guinea is confronted to the increasing risks of bushfires that destroy thousands of hectares of vegetation cover every year. Very little research is devoted to the variability of those fires, which makes it a serious threat to both wildlife and human habitats. The current study investigates the spatial and temporal distribution of bushfires in the period from 2003 to 2016. The method used is the geospatial technology: we first filter pixels corresponding with active light supplied by MODIS images (Moderate Resolution Imaging Spectroradiometer) and estimate their densities following the square meshing procedure. Burned areas are deducted from the estimated pixel densities by calculations. The results highlight great occurrence of fires: 4 to 48 pixels of active fire per year and per 100 km2 depending on the location; 2 to 5 million hectares per year of burned areas (20,000 to 50,000 sqkm). Almost 8 to 24% the size of the whole country. The prefectures of Beyla, Siguiri, Kouroussa, Kankan, Dinguiraye, Mali and Tougue are the most exposed areas. Every year, fire activities are observed as from October and between May and June. They are however mitigated according to the regions (or the geographical domains). Summits of bushfires activities are generally reached between December and January.

ERA-Interim product from the European Center for Medium-Range Weather Forecast (ECMWF) assimilation of African Monsoon Multidisciplinary Analysis (AMMA) resources, Meteosat satellite images, and synoptic observations were used to study local- and regional-scale environments associated with intense convective systems during the AMMA-SOP3 experiment over West Africa in the Northern Hemisphere of summer 2006. The convective system, from the 21st to 23rd of August 2006, was more active at 0000 and 1800 UTC showing diurnal cycle of deep convection over West Africa where the African easterly waves (AEWs) are developed downstream. Downstream barotropic and baroclinic energy conversions associated with strong AEWs are important for the maintenance of AEW activity in West Africa. Barotropic energy conversions dominate south of the African easterly jet (AEJ), while baroclinic energy conversions are most important north of the AEJ. From a dynamical viewpoint, the low-level vorticity presents strong positive values over the sea and Sahara zone, indicating that exists on the cyclonic shear side of the African easterly jet, which is consistent with baroclinic growth. The 925-hPa equivalent potential temperature structure show a maximum over the Sahara which corresponds to the depression observed in this region. A mosaic of three hourly infrared (IR) satellite images, depicts a very distinct signal from an initial region of convection, developing through several stages and moving off the African coast. These observations, along with those available from the World Weather Watch, provide an opportunity to carry out numerical weather prediction (NWP) studies over West Africa utilizing high resolution limited area models.

The relationships between the Canadian Fire Weather Index (FWI) System components and the monthly burned area as well as the number of active fire which has taken from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua/TERRA were investigated in 32 Guinean stations between 2003 and 2013. A statistical analysis based on a multi-linear regression model was used to estimate the skills of FWI components on the predictability of burned area and active fire. This statistical analysis gave performances explaining between 16 to 79% of the variance for the burned areas and between 29 and 82% of the variance for the number of fires (P

Thisstudyaimstoachieveabetterunderstandingoftheinitiationofdeepconvection in the Sahel by using the African Monsoon Multidisciplinary Analyses (AMMA) dataset. Based on the Massachusetts Institute of Technology (MIT) radar, wind profiler,satellitedata,surfacefluxandmeteorologicalstations,wehavecharacterised the atmospheric convection which occurred over Niamey during the onset period of the monsoon. From 6 to 31 July, radar reflectivity fields combined with brightness temperatures were used to classify the type of convection observed each day within a 50km radius of the MIT radar location. Four types of convection have been identified: fair weather (FW) with a clear sky throughout the entire day, shallow convection (SH), afternoon locally initiated deep convection (LC), and propagating deep convection (PC). Subsequently, the mechanisms responsible for the initiation of local deep convection were investigated. Neither early morning convective available potential energy nor the convective triggering potential allowed the onset of local deep convection to be predicted correctly. In effect, they were both favourable to deep convection most of the time, while convective inhibition was typically quite large. Our results show that the daytime growth of the atmospheric boundary layer needed to be sufficient for local deep convection to occur during that period. Convergence lines, which grew within the morning clear-air roll organisation, were found to be precursors of local deep convection. Classes FW, SH and LC ultimately behaved quite similarly, with notable convergence in the lower troposphere, but FW showed smaller boundarylayer growth, and FW and SH classes revealed a significant divergence above the boundary layer. Most cases of LC generated a circular gust front. These density currents almost always generated new convective cells. Copyright c � 2013 Royal

International audience; During 15 August through 30 September 2006 (Special Observing Period 3, SOP3), key weather measurements are obtained from ground and aircraft platforms during the African Monsoon Multidisciplinary Analysis campaign. Key measurements are aimed at investigating African easterly waves (AEWs) and mesoscale convective systems in a coastal environment as they transition to the eastern Atlantic Ocean. Ground and aircraft instruments include polarimetric radar, a coarse and a high-density rain gauge network, surface chemical measurements, 12 m meteorological measurement, broadband IR, solar and microwave measurements, rawinsonde, aircraft dropsonde, lidar, and cloud radar measurements. Ground observations during SOP3 show that Senegal was influenced by 5 squall lines, 6 Saharan air layer intrusions, and 10 AEWs. Downstream tropical cyclones developed were associated with the passage of four AEWs. FA-20 aircraft measurements of microphysical aspects of 22 September squall line and several nondeveloping AEWs over the extreme eastern Atlantic Ocean are presented.