New empirical long-range schemes for the prediction of dates of onset and cessation and of the monthly and annual amounts of rainfall are developed for Kano, in the West African Sahel, using only surface synoptic data. They are based on variations in equivalent potential temperature, q e , which occur as a result of the seasonal, monthly and daily variations of moisture in the summer monsoon flow over West Africa. Agricultural activities may begin about 72 days after the day the anomalies of q e (i.e. q%) first become positive for at least 15 days, essentially signifying the beginning of adequate moisture supply associated with a well established monsoon flow.The new schemes ensure that both the cessation date and the annual amount of rainfall can be predicted prior to the onset of the rains, thus providing, in conjunction with the onset date, very important and useful information for reliable and effective planning of agricultural and water resource activities. Performance tests using an 11-year independent data set indicate that the schemes possess reliable skill.Because the weather over Nigeria is very typical of the entire West African region, being affected by the same wind regime and weather phenomena, these prediction schemes will provide tremendous assistance for enhanced and sustainable agriculture, as well as for efficient water resources management, if extended to the whole area. Furthermore, the methods have the important advantage that, bearing in mind the fact that the majority of West African countries have very sparse, if indeed, any upper-air data, the surface synoptic data needed for their use are readily available in all of the countries.

BackgroundThe terrestrial land surface in West Africa is made up of several types of savanna ecosystems differing in land use changes which modulate gas exchanges between their vegetation and the overlying atmosphere. This study compares diurnal and seasonal estimates of CO2 fluxes from three contrasting ecosystems, a grassland, a mixture of fallow and cropland, and nature reserve in the Sudanian Savanna and relate them to water availability and land use characteristics.ResultsOver the study period, and for the three study sites, low soil moisture availability, high vapour pressure deficit and low ecosystem respiration were prevalent during the dry season (November to March), but the contrary occurred during the rainy season (May to October). Carbon uptake predominantly took place in the rainy season, while net carbon efflux occurred in the dry season as well as the dry to wet and wet to dry transition periods (AM and ND) respectively. Carbon uptake decreased in the order of the nature reserve, a mixture of fallow and cropland, and grassland. Only the nature reserve ecosystem at the Nazinga Park served as a net sink of CO2, mostly by virtue of a several times larger carbon uptake and ecosystem water use efficiency during the rainy season than at the other sites. These differences were influenced by albedo, LAI, EWUE, PPFD and climatology during the period of study.ConclusionThese results suggest that land use characteristics affect plant physiological processes that lead to flux exchanges over the Sudanian Savanna ecosystems. It affects the diurnal, seasonal and annual changes in NEE and its composite signals, GPP and RE. GPP and NEE were generally related as NEE scaled with photosynthesis with higher CO2 assimilation leading to higher GPP. However, CO2 effluxes over the study period suggest that besides biomass regrowth, other processes, most likely from the soil might have also contributed to the enhancement of ecosystem respiration.

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Abstract:In this study, the hourly air temperature differences between City hall (urban) and Okoafo (rural) in Lagos, Nigeria, were calculated using one year of meteorological observations, from June 2014 to May 2015. The two sites considered for this work were carefully selected to represent their climate zones. The city core, City hall, is within the Local Climate Zone (LCZ 2) (Compact midrise) while the rural location, Okoafo, falls within LCZ B (Scattered Trees) in the south-western part on the outskirt of the city. This study is one of very few to investigate urban temperature conditions in Lagos, the largest city in Africa and one of the most rapidly urbanizing megacities in the world; findings show that maximum nocturnal UHI magnitudes in Lagos can exceed 7˝C during the dry season, and during the rainy season, wet soils in the rural environment supersede regional wind speed as the dominant control over UHI magnitude.

Previous measurements of urban energy balances generally have been limited to densely built, central city sites and older suburban locations with mature tree canopies that are higher than the height of the buildings. In contrast, few data are available for the extensive, open vegetated types typical of low-density residential areas that have been newly converted from rural land use. We made direct measurements of surface energy fluxes using the eddy-covariance technique at Greenwood, a recently developed exurban neighbourhood near Kansas City, Missouri, USA, during an intensive field campaign in August 2004. were 253 and 370 W m −2 , respectively for the cloudy and near clear-sky conditions, while mean daily values were 114 for cloudy and 171 W m −2 for near clear-sky conditions, respectively. Midday surface albedo values were 0.25 and 0.24 for the cloudy and near clear-sky conditions, respectively. The site exhibited an angular dependence on the solar elevation angle, in contrast to previous observations over urban and suburban areas, but similar to vegetated surfaces. The latent heat flux (Q E ), sensible heat flux (Q H ), and the residual heat storage Q s terms accounted for between 46-58%, 21-23%, and 18-31% of R n , respectively, for all-sky conditions and time averages. The observed albedo, R n , and Q E values are higher than the values that have been reported for suburban areas with high summer evapotranspiration rates in North America. These results suggest that the rapidly growing residential areas at the exurban fringe of large metropolitan areas have a surface energy balance that is more similar to the rural areas from which they were developed than it is to the older suburbs and city centres that make up the urban fabric to which they are being joined.