In the Cameroonian sudano-sahelian and sahelian zone, karal soils i.e., vertisoils and soils with vertic similarities largely spread on tropical black clay in depressions and fiat sectors. Those black cotton soils are...In the Cameroonian sudano-sahelian and sahelian zone, karal soils i.e., vertisoils and soils with vertic similarities largely spread on tropical black clay in depressions and fiat sectors. Those black cotton soils are out of season＇s sorghum loft, locally called as muskwari. As the staple diet in the Cameroonian dry areas, this crop becomes more and more an alternative to drying or better to climate changes. Till now, those soils are considered to be lacustrine or they are resulting just from weathering, according to pedologic researchs. The purpose of this communication, therefore, is to show the effects of Harmattan on the basis of our field＇s observations, investigations and superficial deposits＇ analysis： granulometry and diffractometry in the laboratory. Harmattan is a dry and stable air mass which originates from the saharian anticyclone. Its participation in edaphics process is very relevant. Indeed, dust storms take place throughout the dry season and vertisoil spreads out on various topographic locations bringing about homogeneity of texture and similarity of mineralogic spectrum. Their high kaolinite content, thin granulometric component （fine sand, silt and clay） are indicative of Aeolian loessial dust deposits. It could not be something else in this area of the most southern saharian blow of the great Saharo-Sahelian GWAS （global wind action system） in sub-equatorial latitudes, in line with the venturi formed by Ennedi and Tibesti mountains.展开更多
The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diamete...The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diameter range 0.5-25 μm have been sampled at Kumasi （6040＇ N, l°34＇ W） in Ghana during the winter months of January-February from 1997 to 2009. The settling atmospheric dust particles observed during the peak Harmattan and the background Harmattan periods are analysed for the mean particle size, number and mass concentrations as well as the particle size-frequency. It is shown that the average daily particle diameter, number and mass concentrations obtained in the peak Harmattan periods are 1.57 ± 0.54 μm, 50 ± 25 particles/cm3 and 1,130 ± 994 μg/m3, respectively, while for the background Harmattan these values are correspondingly, 1.31 ±0.31 μm, 32 ±12 particles/cm3 and 576 ±429 μg/m3, respectively. These experimental results will be useful for the design of ambient air-filters and for understanding the West African climate change.展开更多
Indoor settled harmattan dusts at seven sampling stations from the University of Agriculture Makurdi were collected between November, 2014 to March, 2015 (five months) using the wipe sampling methodology. Gravimetric ...Indoor settled harmattan dusts at seven sampling stations from the University of Agriculture Makurdi were collected between November, 2014 to March, 2015 (five months) using the wipe sampling methodology. Gravimetric measurement of the dust samples from all the sample locations revealed that dust loading within the institution during the period of assessment ranges from 4.475 - 6.533 g/m2. Masses of indoor settled dust were expectedly higher along high traffic, untarred roads and construction sites as well as in older buildings than others during the period of this study. AAS analysis of the dust samples shows that heavy metal concentrations (mg/kg dry weight) throughout the sampling stations during the period of investigation range from 0.2372 - 0.7152 for Cu, 293.6 - 884.9 for Fe, 4.265 - 68.55 for Mn and 4.239 - 42.53 for Zn. The concentrations of all the metals investigated were found to be lower when compared with related values in literature and were within acceptable limits during the period of this study. Pearson correlation matrix also shows positive correlation between the possible metal pairs at 95% level of confidence, indicating a similar source which may be from anthropogenic activities within and outside the area.展开更多
The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations o...The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations of aerosol optical properties over Ilorin (8䓠'N, 4䓢'E), Nigeria. Long-term (1998-2013) records of aerosol optical depth (AOD) and angstrom exponent α, from ground-based Aerosol Robotic Network (AERONET) are used to study the seasonal variability, characteristics and types of aerosol. The study showed that seasonal variations (Harmattan and Summer) result in different aerosol concentration, characteristics, and types. The magnitude and sensitivity of AOD to wavelength are found low in Summer with significant increase during Saharan dust transport season (Harmattan). The average mean AODs are 0.73 ± 0.50, 0.97 ± 0.52 and 0.46 ± 0.29 with corresponding mean angstrom of 0.66 ± 0.36, 0.68 ± 0.34, and 0.64 ± 0.37 for the entire period, Harmattan and Summer seasons. High frequency of occurrence of angstrom exponent below 1 (78% and 81%) which were observed during Harmattan and Summer indicates that the particles are generally coarse in mode. The results revealed that for both Harmattan and Summer seasons, the dominant aerosol was dust (DA) with frequency of occurrence of 82% and 79%. However, mixed aerosol (MIXA) (14.4%) is the second dominant case during Harmattan while in Summer maritime aerosol (MA) (9.1%) associated with transport due to southwesterly trade wind is the second dominant aerosol. This conclusion is supported by size distribution data for the study site which showed that large volume of aerosol particle size are enclosed in largely coarse mode range in all seasons. A 7-day back trajectory seasonal frequency plot sourced from the Hysplit Single Particles Lagrangian Integrated Trajectory model (Hysplit_4 model) shows that dust are transported from the Sahara during north-easterly trade wind flow while the observed marine aerosols are conveyed by the southwesterly trade wind influences to the study site.展开更多
The objective of this work is to study the diurnal evolution of the radiative impact of atmospheric aerosols in an urban city located in the West African Sahel and the correlations with the main influencing factors of...The objective of this work is to study the diurnal evolution of the radiative impact of atmospheric aerosols in an urban city located in the West African Sahel and the correlations with the main influencing factors of local climate dynamics. The simulation was performed using a treatment chain including the GAME code. In the methodology, the atmosphere is modeled by 33 plane parallel layers and the effects of absorption, multiple scattering by particles and gas are taken account. An hour-by-hour calculation of radiative forcing at the top of the atmosphere, in the atmospheric layer and at the earth’s surface was performed. The data used as input are the monthly averages of optical properties, radiosonde measurements, daily synoptic measurements and surface albedo. The results show a parabolic diurnal course of a negative radiative impact at the top of the atmosphere with an extremum at 12 o'clock. Maximum cooling is observed shortly after sunrise and shortly after sunset. The largest annual deviations are noted between the months of March and December with respective maximum cooling values of -34 W/m<sup>2</sup> and -15.60 W/m<sup>2</sup>. On the earth’s surface, a cooling impact is observed with two diurnal peaks at sunrise and sunset, the greatest difference between the diurnal maximums is noted between March (-104.45 W/m<sup>2</sup>) and August (-54 W/m<sup>2</sup>). In the atmospheric layer, there is almost constant diurnal warming between 9 a.m. and 4 p.m. The maximum difference between the diurnal extremes is also noted between March (about 85 W/m<sup>2</sup>) and August (35 W/m<sup>2</sup>). Likewise, the study of the diurnal warming of the first atmospheric layer showed the extreme values in March (5.6°C) and August (2.4°C), these maximum values being always observed at around 12 o’clock. An analysis of similar works carried out in urban cities in various locations of the world has shown a relatively good accordance with the values obtained. This study highlights the radiative impact of Saharan desert dust, the effect of the local climate and the succession between dry season (November to May) and the rainy one (July to October), as well as the zenith solar angle and human activity.展开更多
This study analyzed the impact of the local dry and rainy seasons on diurnal temperature range (DTR), for each major climatic zone of Nigeria namely the tropical monsoon, tropical savannah and semi-arid, using meteoro...This study analyzed the impact of the local dry and rainy seasons on diurnal temperature range (DTR), for each major climatic zone of Nigeria namely the tropical monsoon, tropical savannah and semi-arid, using meteorological data from thirteen observation stations for the period 1981 to 2021. DTR was computed from the difference of minimum temperature from maximum temperature and yearly and forty one years’ monthly averages of DTR and rainfall were computed and plotted in different graphs. The overall results from each climatic zone showed that DTR fluctuates with the seasons and there is an inverse relationship between DTR and rainfall whereby the value of DTR decreases as the rainy season approaches but increases as the rainy season departs ushering in the dry season or conversely DTR increases as the dry season approaches and decreases as the dry season departs ushering-in the rainy season. Secondly, the average yearly patterns of rainfall and DTR are roughly and oppositely shaped parabolas where the peak value of rainfall is diametrically opposite to the trough value of DTR and the least or nil volume of rainfall corresponds to the highest value of DTR. Thirdly, due to the yearly seasonal cycle of dry and rainy seasons in Nigeria coupled with the inverse relationship between DTR and Rainfall, the seasonal plot of DTR and rainfall is also cyclic in pattern with DTR cycle lagging 180 degrees with the rainfall cycle and the intersection of the two cycles represents the departure of one season and onset of another season while each half-cycle represents either the dry or rainy season. Fourthly, the dependence of DTR on any season at hand in Nigeria makes DTR season-forcing. This fourth result is underpinned by a result that showed that the 1981 and 2021 patterns of DTR and 1981 and 2021 patterns of rainfall when compared were similar, the differences were in the volume of rainfall which was due to climate change that has taken place over the four decades and which also impacted DTR since DTR varies inversely with rainfall. Finally and notwithstanding the common grounds of the results stated above, the result further showed that each climatic zone of Nigeria reacts differently to the local and global climate changes leading to the magnitude of DTR and the volume of rainfall being different across climatic zones, with rainfall volume and duration decreasing towards the arid North from the Coastal South while contrariwise DTR increases towards the arid North from the Coastal South.展开更多
Background:Garcinia kola is an indigenous multipurpose tree species commonly found in the tropical rain forest zone of West and Central Africa.Providing economic,ecological,and socio-cultural benefits for people,they ...Background:Garcinia kola is an indigenous multipurpose tree species commonly found in the tropical rain forest zone of West and Central Africa.Providing economic,ecological,and socio-cultural benefits for people,they have potentials to improve the regional and local income generation to the farmers but the cultivation of the species is very limited in Nigeria.Methods:The study investigated cultivation and farmers’perceptions on the impacts of climate change on goods and services provided by G.kola in Nigeria.Structured questioners and interviews were used.The data obtained was analyzed using descriptive and inferential statistic such as frequency,percentage,chi-square,and multinomial logit regressions with SPSS Version 20 and R software Version 3.1.0.Results:The results show that farmers are presently not cultivating G.kola,and most of the available stands were inherited from grandparents.The farmers still believe it is only God that can make G.kola to germinate;however,information about the new improved methods of raising G.kola was not spread across farmers’communities.Over 93%of these farmers were not aware of these new methods,and the only means they raise the species is by picking the wildlings that regenerate naturally close to mother tree and are rarely found.The finding also shows that farmers are well aware of climate change and its impact on crop productivity is not clear to them.The result shows that five explanatory variables(age,gender,marital status,education level,household size and primary occupation)are the main factors significantly influencing farmers’perception of climate change and the cultivation of the G.kola.During interview section,the farmers reported variability of Harmattan season influences fruit production of the species;according to them,increase in Harmattan season usually leads to increase in fruiting of G.kola.Conclusions:Based on our findings,all the 215 respondent interviewed agree that climatic variability influences the availability of G.kola which will in turn have significant effects on the goods and services provided to the people.Efforts should be made at educating the rural farmers on propagation possibilities,potential ecosystem services,and the impact of climate change on multiple-purpose agroforestry species.展开更多
文摘In the Cameroonian sudano-sahelian and sahelian zone, karal soils i.e., vertisoils and soils with vertic similarities largely spread on tropical black clay in depressions and fiat sectors. Those black cotton soils are out of season＇s sorghum loft, locally called as muskwari. As the staple diet in the Cameroonian dry areas, this crop becomes more and more an alternative to drying or better to climate changes. Till now, those soils are considered to be lacustrine or they are resulting just from weathering, according to pedologic researchs. The purpose of this communication, therefore, is to show the effects of Harmattan on the basis of our field＇s observations, investigations and superficial deposits＇ analysis： granulometry and diffractometry in the laboratory. Harmattan is a dry and stable air mass which originates from the saharian anticyclone. Its participation in edaphics process is very relevant. Indeed, dust storms take place throughout the dry season and vertisoil spreads out on various topographic locations bringing about homogeneity of texture and similarity of mineralogic spectrum. Their high kaolinite content, thin granulometric component （fine sand, silt and clay） are indicative of Aeolian loessial dust deposits. It could not be something else in this area of the most southern saharian blow of the great Saharo-Sahelian GWAS （global wind action system） in sub-equatorial latitudes, in line with the venturi formed by Ennedi and Tibesti mountains.
文摘The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diameter range 0.5-25 μm have been sampled at Kumasi （6040＇ N, l°34＇ W） in Ghana during the winter months of January-February from 1997 to 2009. The settling atmospheric dust particles observed during the peak Harmattan and the background Harmattan periods are analysed for the mean particle size, number and mass concentrations as well as the particle size-frequency. It is shown that the average daily particle diameter, number and mass concentrations obtained in the peak Harmattan periods are 1.57 ± 0.54 μm, 50 ± 25 particles/cm3 and 1,130 ± 994 μg/m3, respectively, while for the background Harmattan these values are correspondingly, 1.31 ±0.31 μm, 32 ±12 particles/cm3 and 576 ±429 μg/m3, respectively. These experimental results will be useful for the design of ambient air-filters and for understanding the West African climate change.
文摘Indoor settled harmattan dusts at seven sampling stations from the University of Agriculture Makurdi were collected between November, 2014 to March, 2015 (five months) using the wipe sampling methodology. Gravimetric measurement of the dust samples from all the sample locations revealed that dust loading within the institution during the period of assessment ranges from 4.475 - 6.533 g/m2. Masses of indoor settled dust were expectedly higher along high traffic, untarred roads and construction sites as well as in older buildings than others during the period of this study. AAS analysis of the dust samples shows that heavy metal concentrations (mg/kg dry weight) throughout the sampling stations during the period of investigation range from 0.2372 - 0.7152 for Cu, 293.6 - 884.9 for Fe, 4.265 - 68.55 for Mn and 4.239 - 42.53 for Zn. The concentrations of all the metals investigated were found to be lower when compared with related values in literature and were within acceptable limits during the period of this study. Pearson correlation matrix also shows positive correlation between the possible metal pairs at 95% level of confidence, indicating a similar source which may be from anthropogenic activities within and outside the area.
文摘The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations of aerosol optical properties over Ilorin (8䓠'N, 4䓢'E), Nigeria. Long-term (1998-2013) records of aerosol optical depth (AOD) and angstrom exponent α, from ground-based Aerosol Robotic Network (AERONET) are used to study the seasonal variability, characteristics and types of aerosol. The study showed that seasonal variations (Harmattan and Summer) result in different aerosol concentration, characteristics, and types. The magnitude and sensitivity of AOD to wavelength are found low in Summer with significant increase during Saharan dust transport season (Harmattan). The average mean AODs are 0.73 ± 0.50, 0.97 ± 0.52 and 0.46 ± 0.29 with corresponding mean angstrom of 0.66 ± 0.36, 0.68 ± 0.34, and 0.64 ± 0.37 for the entire period, Harmattan and Summer seasons. High frequency of occurrence of angstrom exponent below 1 (78% and 81%) which were observed during Harmattan and Summer indicates that the particles are generally coarse in mode. The results revealed that for both Harmattan and Summer seasons, the dominant aerosol was dust (DA) with frequency of occurrence of 82% and 79%. However, mixed aerosol (MIXA) (14.4%) is the second dominant case during Harmattan while in Summer maritime aerosol (MA) (9.1%) associated with transport due to southwesterly trade wind is the second dominant aerosol. This conclusion is supported by size distribution data for the study site which showed that large volume of aerosol particle size are enclosed in largely coarse mode range in all seasons. A 7-day back trajectory seasonal frequency plot sourced from the Hysplit Single Particles Lagrangian Integrated Trajectory model (Hysplit_4 model) shows that dust are transported from the Sahara during north-easterly trade wind flow while the observed marine aerosols are conveyed by the southwesterly trade wind influences to the study site.
文摘The objective of this work is to study the diurnal evolution of the radiative impact of atmospheric aerosols in an urban city located in the West African Sahel and the correlations with the main influencing factors of local climate dynamics. The simulation was performed using a treatment chain including the GAME code. In the methodology, the atmosphere is modeled by 33 plane parallel layers and the effects of absorption, multiple scattering by particles and gas are taken account. An hour-by-hour calculation of radiative forcing at the top of the atmosphere, in the atmospheric layer and at the earth’s surface was performed. The data used as input are the monthly averages of optical properties, radiosonde measurements, daily synoptic measurements and surface albedo. The results show a parabolic diurnal course of a negative radiative impact at the top of the atmosphere with an extremum at 12 o'clock. Maximum cooling is observed shortly after sunrise and shortly after sunset. The largest annual deviations are noted between the months of March and December with respective maximum cooling values of -34 W/m<sup>2</sup> and -15.60 W/m<sup>2</sup>. On the earth’s surface, a cooling impact is observed with two diurnal peaks at sunrise and sunset, the greatest difference between the diurnal maximums is noted between March (-104.45 W/m<sup>2</sup>) and August (-54 W/m<sup>2</sup>). In the atmospheric layer, there is almost constant diurnal warming between 9 a.m. and 4 p.m. The maximum difference between the diurnal extremes is also noted between March (about 85 W/m<sup>2</sup>) and August (35 W/m<sup>2</sup>). Likewise, the study of the diurnal warming of the first atmospheric layer showed the extreme values in March (5.6°C) and August (2.4°C), these maximum values being always observed at around 12 o’clock. An analysis of similar works carried out in urban cities in various locations of the world has shown a relatively good accordance with the values obtained. This study highlights the radiative impact of Saharan desert dust, the effect of the local climate and the succession between dry season (November to May) and the rainy one (July to October), as well as the zenith solar angle and human activity.
文摘This study analyzed the impact of the local dry and rainy seasons on diurnal temperature range (DTR), for each major climatic zone of Nigeria namely the tropical monsoon, tropical savannah and semi-arid, using meteorological data from thirteen observation stations for the period 1981 to 2021. DTR was computed from the difference of minimum temperature from maximum temperature and yearly and forty one years’ monthly averages of DTR and rainfall were computed and plotted in different graphs. The overall results from each climatic zone showed that DTR fluctuates with the seasons and there is an inverse relationship between DTR and rainfall whereby the value of DTR decreases as the rainy season approaches but increases as the rainy season departs ushering in the dry season or conversely DTR increases as the dry season approaches and decreases as the dry season departs ushering-in the rainy season. Secondly, the average yearly patterns of rainfall and DTR are roughly and oppositely shaped parabolas where the peak value of rainfall is diametrically opposite to the trough value of DTR and the least or nil volume of rainfall corresponds to the highest value of DTR. Thirdly, due to the yearly seasonal cycle of dry and rainy seasons in Nigeria coupled with the inverse relationship between DTR and Rainfall, the seasonal plot of DTR and rainfall is also cyclic in pattern with DTR cycle lagging 180 degrees with the rainfall cycle and the intersection of the two cycles represents the departure of one season and onset of another season while each half-cycle represents either the dry or rainy season. Fourthly, the dependence of DTR on any season at hand in Nigeria makes DTR season-forcing. This fourth result is underpinned by a result that showed that the 1981 and 2021 patterns of DTR and 1981 and 2021 patterns of rainfall when compared were similar, the differences were in the volume of rainfall which was due to climate change that has taken place over the four decades and which also impacted DTR since DTR varies inversely with rainfall. Finally and notwithstanding the common grounds of the results stated above, the result further showed that each climatic zone of Nigeria reacts differently to the local and global climate changes leading to the magnitude of DTR and the volume of rainfall being different across climatic zones, with rainfall volume and duration decreasing towards the arid North from the Coastal South while contrariwise DTR increases towards the arid North from the Coastal South.
基金The study was funded by West African Climate Change and Adapted Land use programme through the German Federal Ministry for Education and Research.
文摘Background:Garcinia kola is an indigenous multipurpose tree species commonly found in the tropical rain forest zone of West and Central Africa.Providing economic,ecological,and socio-cultural benefits for people,they have potentials to improve the regional and local income generation to the farmers but the cultivation of the species is very limited in Nigeria.Methods:The study investigated cultivation and farmers’perceptions on the impacts of climate change on goods and services provided by G.kola in Nigeria.Structured questioners and interviews were used.The data obtained was analyzed using descriptive and inferential statistic such as frequency,percentage,chi-square,and multinomial logit regressions with SPSS Version 20 and R software Version 3.1.0.Results:The results show that farmers are presently not cultivating G.kola,and most of the available stands were inherited from grandparents.The farmers still believe it is only God that can make G.kola to germinate;however,information about the new improved methods of raising G.kola was not spread across farmers’communities.Over 93%of these farmers were not aware of these new methods,and the only means they raise the species is by picking the wildlings that regenerate naturally close to mother tree and are rarely found.The finding also shows that farmers are well aware of climate change and its impact on crop productivity is not clear to them.The result shows that five explanatory variables(age,gender,marital status,education level,household size and primary occupation)are the main factors significantly influencing farmers’perception of climate change and the cultivation of the G.kola.During interview section,the farmers reported variability of Harmattan season influences fruit production of the species;according to them,increase in Harmattan season usually leads to increase in fruiting of G.kola.Conclusions:Based on our findings,all the 215 respondent interviewed agree that climatic variability influences the availability of G.kola which will in turn have significant effects on the goods and services provided to the people.Efforts should be made at educating the rural farmers on propagation possibilities,potential ecosystem services,and the impact of climate change on multiple-purpose agroforestry species.
