A systematic review of climate change impacts,adaptation strategies,and policy development in West Africa

Climate change studies are diverse with no single study giving a comprehensive review of climate change impacts,adaptation strategies,and policy development in West Africa.The unavailability of an all-inclusive study to serve as a guide for practitioners affects the effectiveness of climate change adaptation strategies proposed and adopted in the West African sub-region.The purpose of this study was to review the impacts of climate change risks on the crop,fishery,and livestock sectors,as well as the climate change adaptation strategies and climate-related policies aimed at helping to build resilient agricultural production systems in West Africa.The review process followed a series of rigorous stages until the final selection of 56 articles published from 2009 to 2023.Generally,the results highlighted the adverse effects of climate change risks on food security.We found a continuous decline in food crop production.Additionally,the livestock sector experienced morbidity and mortality,as well as reduction in meat and milk production.The fishery sector recorded loss of fingerlings,reduction in fish stocks,and destruction of mariculture and aquaculture.In West Africa,climate-smart agriculture technologies,physical protection of fishing,and inclusion of gender perspectives in programs appear to be the major adaptation strategies.The study therefore recommends the inclusion of ecosystem and biodiversity restoration,weather insurance,replacement of unsafe vessels,and strengthening gender equality in all climate change mitigation programs,as these will help to secure enough food for present and future generations.

Socioenvironmental Drivers of Farmers’ Perceptions of Climate Change Risk in Agroforestry Parklands of West Atacora in Benin (West Africa)

Throughout the world, climate change is threatening the human population. In West Africa, smallholder farmers in indigenous agricultural societies typically hold considerable knowledge. Therefore, this study was conducted in West Atacora of Benin Republic to assess the drivers of farmers’ perceptions of climate change risk. We used a random sampling technique to select 360 households’ heads who were interviewed regarding different climate change risks perception. Binomial logistic regression was used to assess the drivers of farmers’ perceptions of climate change risks. The results showed that the farmers in drier areas had a higher perception of the global risk of climate change than those in humid areas. The same trend was observed for the seven different individual’s climate change risk investigated. The study identified also membership of farm organizations as main sociodemographic characteristic that explains farmers’ perception of climate change risk perception. These findings are helpful tools to sensitize the local people on climate change risk and cope with the risk in agricultural lands.

Assessment of ERA5 and ERA-Interim in Reproducing Mean and Extreme Climates over West Africa

In situ data in West Africa are scarce,and reanalysis datasets could be an alternative source to alleviate the problem of data availability.Nevertheless,because of uncertainties in numerical prediction models and assimilation methods,among other things,existing reanalysis datasets can perform with various degrees of quality and accuracy.Therefore,a proper assessment of their shortcomings and strengths should be performed prior to their usage.In this study,we examine the performance of ERA5 and ERA-interim(ERAI)products in representing the mean and extreme climates over West Africa for the period 1981-2018 using observations from CRU and CHIRPS.The major conclusion is that ERA5 showed a considerable decrease in precipitation and temperature biases and an improved representation of inter-annual variability in much of western Africa.Also,the annual cycle is better captured by ERA5 in three of the region’s climatic zones;specifically,precipitation is well-reproduced in the Savannah and Guinea Coast,and temperature in the Sahel.In terms of extremes,the ERA5 performance is superior.Still,both reanalyses underestimate the intensity and frequency of heavy precipitations and overestimate the number of wet days,as the numerical models used in reanalyses tend to produce drizzle more often.While ERA5 performs better than ERAI,both datasets are less successful in capturing the observed long-term trends.Although ERA5 has achieved considerable progress compared to its predecessor,improved datasets with better resolution and accuracy continue to be needed in sectors like agriculture and water resources to enable climate impact assessment.

NDVI-Derived Vegetation Trends and Driving Factors in West African Sudanian Savanna

The Sudanian savanna is a key vegetation biome in West Africa providing food and vital ecosystem services. Recently, it has been reported alarming vegetation loss in this biome, calling for more investigation, relevant to tackle land degradation and ensure food security. However, vegetation dynamics in this area remains a matter of debate, and one of the main challenges is to document consistently the underlying driving factors. This study aimed at assessing vegetation trends and driving factors from 2000 to 2022. NDVI trend, detected using the Mann-Kendall’s monotonic trend test, was used as proxy to express vegetation dynamics. In addition to the non-parametric Spearman correlation analysis, variables importance scores, derived from Random Forest (RF) classifications, were used to determine key driving factors among climatic, topographic, edaphic, accessibility and demographic factors. During 2000-2022, no significant trends largely characterised the vegetation cover of the study area. However, patterns of strong (weak) browning and strong (weak) greening affected 7.1% (10.6%) and 12.8% (19.1%) of the study area respectively. According to the driving factors analysis, the observed vegetation trends were mainly driven by rainfall dynamics (trend and mean annual), population growth and anthropogenic activities. The results of this study can support the development of efficient strategies for safeguarding vegetation cover in the Sudanian savanna of Burkina Faso.

Rainfall Variability and Trends in West Africa

Rainfall variability associated with climate change has enormous impacts on ecosystems, agriculture and people in West Africa but few studies have been devoted to it. Monthly rainfall data from 1901 to 2013, provided by the Global Precipitation Climatology Center dataset, were analyzed using segmentation and empirical modal decomposition (EMD) methods to increase our knowledge on past and recent spatio-temporal rainfall trends and their impacts on the West African region. The results obtained showed that the peak of rainfall during the short rainy season is observed in September in Côte d’Ivoire, Ghana and Liberia. The temporal variability of this rainfall is marked by several breakpoints whose durations range from 2 to 70 years. The periods of change in the rainfall regime, characterized by the appearance of breakpoints, vary from one country to another and are of unequal duration. The main breakpoint appears after 1960. Periods of relative or normal increase or decrease in precipitation are observed before and after 1960. The long-term variability of this rainfall is characterized by a decrease in the amount of rainfall over all West African countries. The results of this study can be used as a tool to help raise awareness among populations for sustainable management of water resources in response to climate change and its adverse effects.

Effects of Bush Fires on Biodiversity in West Africa Sahel: A Review

Bush fire is one of the drivers of biodiversity loss worldwide.However,the impact of bush fires on biodiversity in the West Africa Sahel is not well documented.Therefore,this study reviewed the effects of bush fires on biodiversity,the typology of the bush fire drivers and bush fires solutions in the West Africa Sahel via a systematic review.The authors used many research engines such as Google Scholar and Mendeley from 2010 to 2022 with some keywords in French and English.It comes from the analysis of the data that Mali is the most country affected by bush fires with an average of 35,000,000 ha burned.In Burkina Faso,bush fires burned more than 2 million hectares each year.The analysis showed also a loss of 1,675,157 ha in Niger and 56,568.10 ha in Senegal.The study recommends that climate actions should target bush fires prevention and fighting as climate response in order to promote sustainable biodiversity management in the West Africa Sahel.The study recommends also that West Africa Sahel countries develop bushfire community education programs for fire prevention.

Sensitivity Study of the RegCM4’s Surface Schemes in the Simulations of West Africa Climate

Two simulations of five years (2003-2007) were conducted with the Regional Climate models RegCM4, one coupled with Land surface models BATS and the other with CLM4.5 over West Africa, where simulated air temperature and precipitation were analyzed. The purpose of this study is to assess the performance of RegCM4 coupled with the new CLM4.5 Land surface scheme and the standard one named BATS in order to find the best configuration of RegCM4 over West African. This study could improve our understanding of the sensitivity of land surface model in West Africa climate simulation, and provide relevant information to RegCM4 users. The results show fairly realistic restitution of West Africa’s climatology and indicate correlations of 0.60 to 0.82 between the simulated fields (BATS and CLM4.5) for precipitation. The substitution of BATS surface scheme by CLM4.5 in the model configuration, leads mainly to an improvement of precipitation over the Atlantic Ocean, however, the impact is not sufficiently noticeable over the continent. While the CLM4.5 experiment restores the seasonal cycles and spatial distribution, the biases increase for precipitation and temperature. Positive biases already existing with BATS are amplified over some sub-regions. This study concludes that temporal localization (seasonal effect), spatial distribution (grid points) and magnitude of precipitation and temperature (bias) are not simultaneously improved by CLM4.5. The introduction of the new land surface scheme CLM4.5, therefore, leads to a performance of the same order as that of BATS, albeit with a more detailed formulation.

The Characteristics and Distribution Pattern of Seafloor Sinuous Pockmark Train in the Niger Delta Basin,West Africa

Objective The term ＂pockmark＂ was introduced by King and MacLean （1970） to describe small ＂circular＂ on echosounder records in Nova Scotia. described as circular, near Pockmarks are usually circular or elongated depressions, generally 10--400 m in diameter and 30-50 m in deep. Pockmarks are normally regarded to be manifestations of fluids escape through the seabed. Pockmarks are valuable features on the seafloor and are useful in constraining the hydrodynamics of sedimentary basins. Since then pockmarks have been recognized in many areas around the world. They occur predominantly in fine-grained siliciclastic depositional settings, although a few case studies have been reported in carbonate settings. In this paper we illustrate a suite of fluid escape features, discovered during the course of petroleum exploration on the West Africa continental margin （Fig. 1）. They are particularly of interest to the oil and gas industry because they could be potential indicators of deeply buried hydrocarbon reservoirs, and fluid flow phenomena in the deep water oilfield are important for the safe and efficient exploration, development and production of hydrocarbons in the area.

The Fintech Revolution: An Opportunity for the West African Financial Sector

Fintech provides alternative solutions and business models that could render traditional banking processes obsolete. This paper assesses the opportunity that could be taken to West Africa by using Fintech’s financial system. It describes the current West African financial sector, the way of digitization settlement, and lastly, the financial market segments of Fintech. Financial sector creates a massive amount of data exploiting by Fintech companies that are using to segment customer populations, identify opportunities for new products and services and optimize pricing. In this segment, products may use data and analytics to computerize the decision- making processes. Innovative start-ups, retailers, established banks, card companies and other payment services providers are the Payment systems that underpin the services that enable funds to be transferred between people and institutions. For the financial system (banking), Fintech offers sustainable and realistic opportunities by enhancing the value proposition and driving sales, reducing operating costs, making easy access to loans, and lowering interest rates. After showing the advantages of using Fintech services, the findings are that Fintech could improve both financial services and access to services in the West African economy.

New Approach of Structural Setting of Gold Deposits in Birimian Volcanic Belt in West African Craton: The Example of the Sabodala Gold Deposit, SE Senegal

The Sabodala gold deposit in the Mako volcanic Belt (SE-Senegal, West African Craton) occurs in mafic and ultramafic rocks overlain by clastic sedimentary rocks and felsic volcanic-volcaniclastic sequences. It is a structurally controlled mesothermal vein gold deposit developed in deformed rocks units near the Falombo pluton. The Sabodala Goldfield comprises several faults systems striking N-S to NE-SW. New structural evolution consisting of both thrusting and transcurrent events has been defined for the Sabodala Goldfield. The majority of the gold at Sabodala occurs on the western flank of a large, doubling plunging dome (the Sabodala Antiform) and is also associated with sinistral wrenching that overprints early structures within the Sabodala Mine. The gold bearing veins are hosted by flat lying and NW-trending shear zones. The NW-trending faults acted as transfers syn-gold mineralization, although only discrete segments of these faults were active during the main stage of gold mineralization. Late exhumation resulted in extension along fault zones was responsible for the juxtaposition of medium and low grade metamorphic rocks. The granitic suite of the Falombo pluton is linked to exhumation. Final dextral transpression postdating exhumation produced shearing and folding. Gold lodes developed during brittle deformation are associated with high fluid pressures in a northwest-southeast shortening regime. These are termed mainly the Sabodala deposit, and secondary the Niakafiri and Masato deposits.

Assessment of Intra-Seasonal Variability and Trends of Precipitations in a Climate Change Framework in West Africa

Climate change has led human beings to take an interest in the study of meteorological and climatic phenomena. In fact, the main impact of climate change on different sectors of society is caused by extreme events since the occurrence of extreme events leads to more impact related to change in mean climate. Unfortunately, the West African region is vulnerable to extreme rainfall impact because its economy is based on rain-fed agriculture. This study examined the seasonal variability of extreme rainfall in West Africa. Eight (8) climate indices were chosen from among the 27 defined by the Expert Team on Climate Change Detection and Indices (ETCCDI). The nonparametric Mann-Kendall test was used to assess the seasonal trends. The indices of the same types (frequency or intensity) were compared to assess the intra-seasonal variation of extreme precipitation. The results indicate that, regardless of the season, the Gulf of Guinea receives more rainfall than the Sahel. This phenomenon is due to the fact that the coastal part of West Africa is under the influence of evaporation which is observed at the Atlantic Ocean and during the monsoon, while the other part is dominated by the desert. Mann-Kendall’s test revealed upward and downward trends during each season. The increase in extreme rainfall trends in the number of consecutive dry days suggests that droughts, due to global warming, could be observed and could have severe consequences in terms of water availability, energy supply, agricultural yields and ecosystems in West Africa. In addition, it can lead to the loss of biodiversity and health issues. It is therefore essential for policymakers or decisions makers to determine strategies and mitigation measures against climate change and its impacts on populations.

Improvement of Rice Production under Drought Conditions in West Africa:Application of QTLs in Breeding for Drought Resistance

Rice plays a paramount role in food and nutrition security in many West African countries.Despite the doubling of production during the last decade,rice consumption has grown faster,creating a deficit between the demand and supply.Although the West African sub-region remains the main rice-producing centre on the continent,production is severely hampered by biotic and abiotic stresses.Drought is one of the factors that most severely reduce grain yields of rice.Systems of production need to be established in order to mitigate yield loss as a result of drought.This review discusses the effects of drought on rice production in West Africa and its mitigation with an emphasis on the improvement of tolerance to drought stress.Yield stability can be achieved by developing drought-tolerant varieties through several processes encompassing profiling of known QTLs and identification of new ones,marker-assisted selection,genomic selection,and extensive multi-locational yield trials.We suggest a comprehensive strategy for breeding drought-tolerant rice varieties in West Africa.

Spatial distribution and impacts of climate change on Milicia excelsa in Benin,West Africa

African teak(Milicia excelsa(Welw.)C.C.Berg)is an endangered multi-use species.Understanding the impact of climate change on the distribution of this species may improve the ability to anticipate or recognize its decline or expansion and to take appropriate conservation measures if necessary.Ecological niche modeling was projected in geographical space to study the current and future distribution of M.excelsa in Bénin.MaxEnt was used to estimate the potential geographic distribution of the species under two Representative Concentration Pathways(RCP).Miroc 5 summaries and two RCP 4.5 and RCP 8.5 scenarios were used as predictor variables for projections of the geographic potential of this species.The performance of the model was assessed by the area under the curve(AUC),true skill statistics(TSS)and partial receiver operating characteristics(Partial ROC).From the results,M.excelsa was more a secondary species in the Guinean climatic zone and part of the Sudanian-Guinean and Sudanian climatic zone.The projections show a signifi cant decrease in suitable habitats for the species from the two RCP scenarios.Only a part of the Guinean climatic zone remained suitable and few protected areas will conserve in situ M.excelsa.For the sustainable conservation of M.excelsa,it is essential to strengthen the protection of sacred forests located in the Guinean climatic zone.

Spatiotemporal Evolution of West Africa's Urban Landscape Characteristics Applying Harmonized DMSP-OLS and NPP-VIIRS Nighttime Light(NTL)Data

Investigating urban expansion patterns aids in the management of urbanization and in ameliorating the socioeconomic and environmental issues associated with economic transformation and sustainable development.Applying Harmonized Defense Meteorological Satellite Program-Operational Line-scan System(DMSP-OLS)and the Suomi National Polar-Orbiting Partnership-Visible Infrared Imagery Radiometer Suite(NPP-VIIRS)Nighttime Light(NTL)data,this paper investigated the characteristics of urban landscape in West Africa.Using the harmonized NTL data,spatial comparison and empirical threshold methods were employed to detect urban changes from 1993 to 2018.We examined the rate of urban change and calculated the direction of the urban expansion of West Africa using the center-of-gravity method for urban areas.In addition,we used the landscape expansion index method to assess the processes and stages of urban growth in West Africa.The accuracy of urban area extraction based on NTL data were R^(2)=0.8314 in 2000,R^(2)=0.8809 in 2006,R^(2)=0.9051 in 2012 for the DMSP-OLS and the simulated NPP-VIIRS was R^(2)=0.8426 in 2018,by using Google Earth images as validation.The results indicated that there was a high rate and acceleration of urban landscapes in West Africa,with rates of 0.0160,0.0173,0.0189,and 0.0686,and accelerations of 0.31,0.42,0.54,and 0.90 for the periods of 1998–2003,2003–2008,2008–2013,and 2013–2018,respectively.The expansion direction of urban agglomeration in West Africa during 1993–2018 was mainly from the coast to inland.However,cities located in the Sahel Region of Africa and in the middle zone expanded from north to south.Finally,the results showed that the urban landscape of West Africa was mainly in a scattered and disordered’diffusion’process,whereas only a few cities located in coastal areas experiencing the process of’coalescence’according to urban growth phase theory.This study provides urban planners with relevant insights for the urban expansion characteristics of West Africa.

Analysis of the Fruit Value Chain of Two Priority Food Woody Species of Central Southern Niger, West Africa

Non-timber forest products provide important socio-economic services to different village and urban communities in West Africa. However, little is known about the links between the different actors and their contribution to the local or national economy. This study was conducted in central southern Niger and aimed to 1) identify and map the main actors in the value chain of Ziziphus mauritiana and Balanites aegyptiaca fruits;and 2) analyse the silvicultural and socio-economic aspects of fruit exploitation of these two species. Socio-economic surveys were conducted in four big villages in two main agroecological zones. Fruit exploitation of these two species affected 3044 people, with estimated 39 tonnes of Z. mauritiana and 27 tonnes of B. aegyptiaca fruit collected in 2017. The surveys revealed that the main actors were women (62.05%), constituting the primary core of the actors of the value chain. Exploitation was mainly conducted in forests (68.6%) or on farms (15.4%) with no restrictions to access. Marketing of Z. mauritiana concerned fresh fruit (68.8%) and fruit processed into biscuits (82.14%), and that of B. aegyptiaca involved fruit (38.5%) and oil extracted from seeds (38.7%);the net margin was estimated at 71.71% ± 21.59% for the first species and 50.31% ± 47.99% for the second. The income was mainly used for the needs of farmers’ households. Links have been identified where consumers and processors supply seeds, after extracting the fruit pulp, to nurserymen for the production of plants for the villages or farms. This study reveals an important potential and opportunity for job creation and improved food and nutritional status of the vulnerable strata of rural communities in Niger. Improving the links between the various actors will establish a more sustainable promotion of the fruits of these two species.

Morphometric Differentiation between Two Closely Related Achatinid Snails (Gastropoda: Achatinidae) of West Africa and Implications for the Conservation of <i>Achatina togoensis</i>(Bequaert &Clench, 1934)

Achatina togoensis is a giant land snail taxa endemic to the northern sectors of the Monts Togo, which has been regarded as full species or subspecies of the highly variable, widespread A. achatina (L.). To address this issue, samples of snails were taken throughout the distribution range of the two taxa in the Dahomey Gap (West Africa) and separated into 112 A. achatina and 141 A. togoensis according to color of the columella and parietal wall. Radulae were compared and shell characters of these 2 species were evaluated through the traditional morphometric method. The results indicate that the species cannot be distinguished by overall shell size and radular morphology, but they exhibit significant differences in shell shape and meristic traits. The typical A. achatina with vinaceous-red columella has a low-spired shell and an expanded aperture (globose shape) whereas A. togoensis has a higher-spired and smaller aperture (a fusiform shape). We suggest that local environmental effects are probably the causes of morphological divergence between the two taxa. It is likely that peripheral populations of the typical form of A. achatina would have isolated and developed in the drier facies of the humid forest that individualized in the northern sector of the mountains after the arid or interpluvial period of Holocene. In addition, we find that A. togoensis meets the criteria B2ab (ii, iii) to categorize as “Endangered”. However, whether this latter should be considered as separate species cannot be decided at the current state of knowledge.

Spatial Availability of Nitrogen and Pesticides in the Surface Layers of Agricultural Soils of Tropical Hydrosystems in the Wet Season: Case of the BéréWatershed in Côte d’Ivoire (West Africa)

The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems to the spatial availability of nitrogen and pesticides during the wet season, such as the Béré watershed (BW) in C?te d’Ivoire. For this purpose, after mapping the spatial distribution of the BW cropping systems based on the likelihood classification methodology of satellite images of the study area, 27 samples from the 0 - 20 cm horizon of the soil surface layers of the agricultural areas were taken during the wet and agricultural season of the year 2016. The Kjeldahl method has been used to evaluate the total nitrogen concentration and high-performance liquid chromatography (HPLC) chain made it possible for the analysis of pesticide residues in the soil solutions. Geostatistical analysis and processing of spatial data and physicochemical and agrochemical soil parameters revealed that two major agricultural areas stand out in the BW, namely the Béré upstream watershed (BUW) dominated at 32.65% by annual croppings (maize, cotton, rainfed or lowland rice, market gardening, etc.) and the Béré downstream watershed (BDW) by large areas of perennial croppings (cashew nuts, cocoa, etc.), i.e. 21.47%. Agricultural soils in BW are usually of the moderately desaturated ferralitic type with a low acid pH and a quite strong temperature, such as those of tropical soils’ characteristics. However, agricultural soils in the BUW are characterized by higher proportions of sand and coarse sand. The parameters such as total porosity, cation exchange capacity, clay, organic matter, silt, fine silt, coarse silt, and potassium ions, are higher in the soils of the agricultural area of the BDW. Moreover, soils in the agricultural areas of the BUW are less rich in total nitrogen (0.84 g·kg-1) in contrast to those of the BDW (1.2 g·kg-1). On the other hand, the median concentrations of total pesticides remain very high in the BUW (193.80 μg·kg-1) in front of those of the BDW (94.81 μg·kg-1). In addition, the biological family of herbicides was the most notable in BW. The chemical families of triazines (100% detection;79.37 μg·kg-1) are the most important in the agricultural area of the BUW with the very significant presence of active molecules of pesticides such as simazine (92.86% detection;13.17 μg·kg-1). However, in the BDW, urea substitute (100% detection;44.02 μg·kg-1) dominate, including the active substance chlortoluron (84.62% detection;10.12 μg·kg-1). The presence and abundance of nitrogen and pesticides in the soils of the agricultural areas of BW are strongly linked to the intensive use of these agrochemicals in cropping systems in recent decades in West African countries, even though most of the active molecules found are forbidden in several countries, especially in European countries. These are applied to tropical agricultural soils with physicochemical characteristics favorable to their retention in wet weather, as confirmed by the case of BW’s agricultural soils. Therefore, the BW’s water resources present worrying risks of contamination during rainy events that deserve to be assessed and monitored. Hence the need to take mitigating measures to this effect in order to preserve the quality of the environment.

Research on the implementation of West Africa-North Africa grid interconnection using new electricity-water composite transmission technology

Combining the characteristics of the reverse distribution of solar resources and water resources in North Africa,West Africa and the Sahara,this paper proposes the West Africa-North Africa grid interconnection project to realize the optimal configuration of desert solar resources and surrounding water resources,and introduce the water resources of West Africa's Niger River and North Africa's desalinated seawater to improve the living environment and development conditions in the hinterland of the Sahara Desert;build photovoltaic bases along the route to send clean electricity to North Africa and West Africa.This paper studies the transmission channel path,electricity-water composite transmission technology and project scheme,and analyzes the economics of the project and the water supply and demand conditions of the Niger River.The research results show that it is feasible in hydrological characteristics to lead the Niger River water along the power transmission channel that crosses the Sahara Desert,and the new electricity-water composite transmission technology has obvious economic advantages.

Characterization of Surface Layer Turbulence across a West African Tropical Climate Belt

This study surveyed the levels of boundary layer surface turbulence across a West African climate region. Five years (2011-2015) temperature and wind speed data at synoptic hours 0000 Hr, 0600 Hr, 1200 Hr and 1800 Hr within 0.125° grid resolution was sourced from Era-Interim Reanalysis platform at 1000 mbar pressure level. Using the Richardson (Ri) number technique, results showed that mechanical turbulence of Ri range 0.04 - 0.57 dominates across the surface layer for study locations of Port Harcourt, Enugu, Jos, Kano and Maiduguri than thermal turbulence. However, the least turbulent area was the coastal zone of surveyed region. Results also indicated that the vertical height (L) at which thermal turbulence replaces mechanical turbulence across study locations ranged from 20 - 250 m with lowest replacement levels (20 - 50 m) occurring mainly in the coastal area of Port Harcourt during periods of dawn. The most turbulent periods in the southern coastal location of study region were during key rainy periods from June-August while that for the rest far northern inland areas occur during the dry season/early rainy periods i.e. November-May. The implication of the lower surface turbulence/replacement level within coastal domains most especially during periods of dawn is that emission releases near surface layer will be dispersed after initial rise due to buoyancy at horizontal levels thereby increasing ground level pollutants concentration across sensitive receptors that are close to emission source. At heights of thermal turbulence replacement, emission releases will be transported vertically and then dispersed further away from emission sources, thus impacting sensitive receptors at farther distances. This is the atmospheric boundary layer dynamics that makes ground level pollution worse in the coastal city of Port Harcourt in recent times during periods of dawn. Efforts must be made by concerned Stakeholders towards ensuring that emissions are reduced during the periods of dawn within and around coastal environments.

Long-Term Behaviour of Temperature in the Lower Atmosphere of Niamey a West African Tropical Station

This paper highlights the global warming of the lower atmosphere of West African tropical area using in-situ data. The study is based on the analysis of 500-m interval vertical profiles of radiosonde temperature above Niamey (13.47°N;2.16°E) a sub-Saharan meteorological station. The annual cycle of surface temperatures shows seasonally two peaks located in April/May and in October and two minimum in December/January and August respectively. In the mid-troposphere (between 5 km and 10 km height), time series of monthly mean temperatures from January 2001 to December 2018, shows an annual variability with a slight downward trend of -0.036°C per decade. In the lower stratosphere (25 - 30 km altitude) a cooling of -0.64°C/decade is observed. Temperatures time series also highlight the presence of two breaking points associated with the El Niño-Southern Oscillation (ENSO) events. When performing a separation regarding Southern Oscillation Index (SOI) time series, model parameters of the linear regression indicate a tropospheric warming during the neutral and La Niña phases and a stratospheric cooling. The analysis of the lower stratosphere zonal wind highlights different behaviours of the quasi-biennial oscillation (QBO) during the neutral and La Niña phases.