Publication

Publisher:
 Springer International Publishing
Publication Type:
 Journal
Publication Title:
 The Influence Of Global Climate Drivers On Monsoon Onset Variability In Nigeria Using S2S Models
Publication Authors:
 Eniola Olaniyan, Elijah A Adefisan, Ahmed A Balogun, Kamoru A Lawal
Year Published:
 2019
Abstract:
Rainfall onset has a lot of implications on the sustainability of the socio-economic activities in Nigeria. This study assesses the skills of CMA, ECMWF, and UKMO sub-seasonal-to-seasonal (S2S) models in predicting monsoon onset and its variability over Nigeria. It also investigates the global drivers modulating the variability and their teleconnections with rainfall onset anomaly. All the models, their ensemble members, and the observations were subjected to quantitative statistical analyses from 1998 to 2016. Results show that the three models are able to simulate the Northwards migration of the onset dates adequately with inherent biases and unique characteristics. They are also able to capture the evolution and variability of the global drivers modulating the monsoon onset. While CMA and the ECMWF models improve progressively towards the Sahel, the UKMO model performance is best over the Gulf of Guinea. In addition, despite the fairly poor performance of the models in predicting the variability of onset dates over the Gulf of Guinea and the Sahel, there is a considerable improvement in the correlation skill of the models over the Savannah. Furthermore, results show that only the ECMWF model was able to produce the strength of both the African Easterly Jets (AEJ) and the Tropical Easterly Jet (TEJ) in spatio-temporal mode. These are two of the crucial global drivers modulating the dynamics of West African monsoon. It was also found out that most global drivers, especially the Inter-tropical Discontinuity (ITD) and the Sea Surface Temperature (SST) over the Central Pacific, exhibit direct teleconnection with the onset anomaly. This direct relationship is shown to be strongest over both the Gulf of Guinea and the Sahel. Although the CMA model might have the least skill, it, however, showed that all the S2S models, despite the inherent biases, are able to predict rainfall onset over Nigeria, within the sub-seasonal timescale. Finally, the results show that improvements in multi-model ensembles are valuable added information able to significantly improve model performance. 
Publisher:
 The Soil Science Society Of America, Inc.
Publication Type:
 Journal
Publication Title:
 The WASCAL Hydrometeorological Observatory In The Sudan Savanna Of Burkina Faso And Ghana
Publication Authors:
 Jan Bliefernicht, S Berger, S Salack, S Guug, L Hingerl, D Heinzeller, M Mauder, R Steinbrecher, G Steup, AY Bossa, M Waongo, E Quansah, AA Balogun, Y Yira, J Arnault, Sven Wagner, C Klein, U Gessner, K Knauer, Annette Straub, R Schönrock, R Kunkel, EC Okogbue, A Rogmann, F Neidl, C Jahn, B Diekkrüger, A Aduna, B Barry, Harald Kunstmann
Year Published:
 2018
Abstract:
Watersheds with rich hydrometeorological equipment are still very limited in West Africa but are essential for an improved analysis of environmental changes and their impacts in this region. This study gives an overview of a novel hydrometeorological observatory that was established for two mesoscale watersheds in the Sudan Savanna of Southern Burkina Faso and Northern Ghana as part of the West African Science Service Centre on Climate Change and Adapted Land Use (WASCAL) program. The study area is characterized by severe land cover changes due to a strongly increasing demand of agricultural land. The observatory is designed for long-term measurements of >30 hydrometeorological variables in subhourly resolution and further variables such as CO2. This information is complemented by long-term daily measurements from national meteorological and hydrological networks, among several other datasets recently established for this region. A unique component of the observatory is a micrometeorological field experiment using eddy covariance stations implemented at three contrasting sites (near-natural, cropland, and degraded grassland) to assess the impact of land cover changes on water, energy, and CO2 fluxes. The datasets of the observatory are needed by many modeling and field studies conducted in this region and are made available via the WASCAL database. Moreover, the observatory forms an excellent platform for future investigations and can be used as observational foundation for environmental observatories for an improved assessment of environmental changes and their socioeconomic impacts for the savanna regions of West Africa. 
Publisher:
 Frontier
Publication Type:
 Journal
Publication Title:
 Evaluation Of The ECMWF Sub-seasonal To Seasonal Precipitation Forecasts During The Peak Of West Africa Monsoon In Nigeria
Publication Authors:
 Eniola Olaniyan, Elijah A Adefisan, Feyi Oni, Earnest Afiesimama, Ahmed A Balogun, Kamoru A Lawal
Year Published:
 2018
Abstract:
Motivated by the increasing needs for reliable seasonal climate forecasts for enhanced living and protection of property, this study evaluates the predictive skill of the European Center for Medium-range Weather Forecast's Sub-seasonal to Seasonal (ECMWF-S2S) precipitation forecasts during the peak of West Africa Monsoon in Nigeria. It investigates the ability of the ECMWF-S2S model to reproduce the atmospheric dynamics that influence the monsoon variability in West-Africa. Rain gauge values of 46 meteorological stations and 10-member ensemble of ECMWF-S2S forecasts from the Ensemble Prediction System (EPS) version of the ECMWF were subjected to quantitative statistical analyses. Results show that the model has weak capability in predicting wind strength at 700 mb level to depict the African Easterly Jet (AEJ). However, irrespective of the ENSO phases, ECMWF-S2S model is capable of adequately and reliably predicting the latitudinal positions of the Inter-Tropical Discontinuity (ITD), mean sea level pressure component of the thermal lows and sea surface temperature (SST) anomalies over the Pacific and Atlantic Oceans. On inter-annual time-scales, results also show that ECMWF-S2S model performs best over the Savannah in forecasting of rainfall anomalies (synchronization = 75%) and over the Sahel in the prediction of rainfall accumulation. The model may however not be able to forecast extreme precipitation reliably because the disagreement between the model's ensemble members increases as higher rainfall accumulation values are attained. The implication here is that the reproducibility of the atmospheric dynamic by the model is a better measure of rainfall prediction than the actual quantitative rainfall forecasts especially in areas south of latitude 10°N. The study therefore suggests considering some climate driving mechanisms as predictability sources for the ECMWF-S2S model to enable the atmospheric dynamics to be better represented in the model. 
Publisher:
 Hindawi
Publication Type:
 Journal
Publication Title:
 Numerical Simulation Of Surface Energy And Water Balances Over A Semiarid Grassland Ecosystem In The West African Savanna
Publication Authors:
 Emmanuel Quansah, Genki Katata, Matthias Mauder, Thompson Annor, Leonard K Amekudzi, Jan Bliefernicht, Dominikus Heinzeller, Ahmed A Balogun, Harald Kunstmann
Year Published:
 2017
Abstract:
To understand surface energy exchange processes over the semiarid regions in West Africa, numerical simulations of surface energy and water balances were carried out using a one-dimensional multilayer atmosphere-SOil-VEGetation (SOLVEG) model for selected days of the dry and rainy seasons over a savanna grassland ecosystem in Sumbrungu in the Upper East region of Ghana. The measured Bowen ratio was used to partition the residual energy into the observed sensible heat flux (????) and latent heat flux (LE) in order to investigate the impact of the surface energy closure on model performance. The results showed that the model overall reproduced the diurnal changes in the observed energy fluxes, especially the net radiation (Rn), compared to halfhourly eddy covariance flux measurements, for the study periods. The performance measure in terms of the correlation coefficient (????), centred root mean square error (RMSE), and normalized standard deviation (????) between the simulated ???? and LE and their corresponding uncorrected observed values ranged between R = 0.63–0.99 and 0.83–0.94, RMSE = 0.88–1.25 and 0.88–1.92, and ???? = 0.95–2.23 and 0.13–2.82 for the dry and rainy periods respectively, indicating a moderate to good model performance. The partitioning of ???? and LE by SOLVEG was generally in agreement with the observations during the dry period but showed clear discrepancies during the rainy period, particularly after rainfall events. Further sensitivity tests over longer simulation periods (e.g., 1 year) are required to improve model performance and to investigate seasonal exchanges of surface energy fluxes over the West African Savanna ecosystems in more details. 
Publisher:
 Elsevier
Publication Type:
 Journal
Publication Title:
 Modelling The Effect Of Tree-shading On Summer Indoor And Outdoor Thermal Condition Of Two Similar Buildings In A Nigerian University
Publication Authors:
 Tobi Eniolu Morakinyo, KWD Kalani C Dahanayake, Olumuyiwa Bayode Adegun, Ahmed Adedoyin Balogun
Year Published:
 2016
Abstract:
Using field measurement and numerical simulation techniques, this study assessed the impact of tree-shading on indoor and outdoor summer thermal conditions of two similar buildings at the Federal University of Technology Akure (FUTA), Nigeria. One of the buildings was shaded by trees, while the other was unshaded. For the numerical simulation, outdoor micro-climate model, ENVI-met and Building Energy Simulation (BES) program, EnergyPlus were integrated. This modelling approach was validated using simultaneously observed air temperature and relative humidity data inside and outside both buildings during the summer period (September–November) of year 2010. Model performance statistics results indicate reasonable agreement between simulated and observed micro-climatic data at the indoor and outdoor of both buildings. The integrated models captured the evolution and magnitude of a warm-humid micro-climate of West Africa sub-region and impact of tree-shades on local thermal comfort. Furthermore, micro-scale relationship between non-radiation based thermal comfort indices (Temperature-Humidity Index, THI and Wet Bulb Globe Temperature, WBGT) and Physiological Equivalent Temperature, PET at the interior and exterior of both buildings was investigated. Result suggests preference of WBGT to THI for the assessment of local thermal condition where technical instrumentation (required for PET estimation) and/or model capability is lacking irrespective of shading condition and environment (indoor or outdoor). 
Publisher:
 Multidisciplinary Digital Publishing Institute
Publication Type:
 Journal
Publication Title:
 Urban-rural Temperature Differences In Lagos
Publication Authors:
 Vincent Ojeh, A Balogun, A Okhimamhe
Year Published:
 2016
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. 
Publisher:
 SAGE Publications
Publication Type:
 Journal
Publication Title:
 The Effect Of Vegetation On Indoor And Outdoor Thermal Comfort Conditions: Evidence From A Microscale Study Of Two Similar Urban Buildings In Akure, Nigeria
Publication Authors:
 Tobi Eniolu Morakinyo, Olumuyiwa Bayode Adegun, Ahmed Adedoyin Balogun
Year Published:
 2016
Abstract:
This study assessed thermal conditions in and around two typical buildings on a university campus in Akure, Nigeria. One of the buildings was shaded by trees, while the other was unshaded. The aim is to evaluate the effect of vegetation (tree shading) on indoor and outdoor thermal comfort. Air temperature and relative humidity were measured simultaneously inside and outside both buildings for six months (September 2010 to February 2011). Results show that the unshaded building is generally less comfortable in comparison with the tree-shaded one, especially during the daytime. The unshaded building becomes less comfortable as early as 10:00?h during the dry season, and that can even extend till around 18:00?h during the wet season. Also, the outdoor area around the tree-shaded building is more thermally comfortable than around the unshaded one, irrespective of the season. A strong relationship between outdoor and indoor comfort conditions, irrespective of seasonal or diurnal variations and thermal comfort index, also emerged. While the positive role of tree shading in thermal comfort is not new, this study contributes additional evidence from an understudied sub-Saharan African region like Nigeria. It points to the need for tree planting (greening) as a means to improve thermal comfort in Nigerian cities. 
Publisher:
 BioMed Central
Publication Type:
 Journal
Publication Title:
 Carbon Dioxide Fluxes From Contrasting Ecosystems In The Sudanian Savanna In West Africa
Publication Authors:
 Emmanuel Quansah, Matthias Mauder, Ahmed A Balogun, Leonard K Amekudzi, Luitpold Hingerl, Jan Bliefernicht, Harald Kunstmann
Year Published:
 2015
Abstract:
The 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. Over 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. These 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. 
Publisher:
 Scientific Research Publishing
Publication Type:
 Journal
Publication Title:
 Changes In Vegetation And Rainfall Over West Africa During The Last Three Decades (1981-2010)
Publication Authors:
 Adama Bamba, Bastien Dieppois, Abdourahamane Konaré, Thierry Pellarin, Ahmed Balogun, Nadine Dessay, Bamory Kamagaté, Issiaka Savané, Arona Diédhiou
Year Published:
 2015
Abstract:
The decadal variability of rainfall and vegetation over West Africa have been studied over the last three decades, 1981-1990, 1991-2000 and 2001-2010 denoted as 1980s, 1990s and 2000s, respectively. Climate Research Unit (CRU) monthly precipitation and Normalized Difference Vegetation Index (NDVI) from the National Oceanic and Atmosphere Administration (NOAA), all covering the period 1981-2010 have been used. This study aimed to assess the changes in the land surface condition and the spatio-temporal distribution of rainfall over West Africa region. The relationship between rainfall and vegetation indices over this region was determined using Pearson’s correlation. Also, the decadal comparison between rainfall and NDVI over the region was based on the significant t-test and the Pearson’s correlation. Results showed that significant return to wet conditions is observed between decade 1980s and decade 1990s over West Africa, and also during decade 2000s with the exception of central Benin and the western Nigeria. Meanwhile, a regreening of the central Sahel and Sudano-Sahel regions is noted. From 1990s to 2000s, this regreening belt is located in the South and the coastal areas: the Guinea Coast, Sudano-Guinea and western Sahel regions. A northward displacement of this re-greening belt is also detected. Thus, a linear relationship occurs between rainfall and NDVI in the Sudanian savannah region, but it is not the case in the rest of West Africa. This may suggest that the re-growth of vegetation in the Sudanian savannah region may be linked to rainfall supplies. Therefore, re-greening over Sahel region in 1990s is related to rainfall recovery. However, this re-greening was not sustained in the decade 2000s due to a slight decrease in rainfall. 
Publisher:
 Elsevier
Publication Type:
 Journal
Publication Title:
 Effect Of Tree-shading On Energy Demand Of Two Similar Buildings
Publication Authors:
 Ahmed Adedoyin Balogun, Tobi Eniolu Morakinyo And Olumuyiwa Bayode Adegun
Year Published:
 2014
Abstract:
This study investigates the effect of tree-shading on energy demand in two similar buildings. Outdoor and indoor air temperature was measured simultaneously for a period of 6 months. Five different base temperatures ranging from 20 °C to 25 °C were chosen and used to calculate cooling degree-days. Degree-day and cooling/warming rate methods were used to estimate cooling energy requirements for the two buildings. Indoor and outdoor cooling degree days were observed to be more for the un-shaded buildings compared to the tree-shaded one. Indoor warming and cooling rate show that the un-shaded building warms earlier and faster than the tree-shaded. Results indicate that tree-shading can save up to 34,500 NGN (US$218) on energy costs. The study shows the role of greening in reducing energy demand in buildings.