DSpace Repository :: Browsing by Author "Oguntunde, Philip G."

Browsing by Author "Oguntunde, Philip G."

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Atmospheric modeling and integration between meteorology and hydrology
(GLOWA, 2002-04) D Burose,; Friesen, J.; Intsiful, J.; Jung, G.; Kunstmann, H.; Moene, A.; Oguntunde, Philip G.; Van de Giesen, N.
Understanding feedback mechanisms between atmosphere and land surface is crucial for predicting impact of global change on the regional hydrological cycle. Unfortunately, meteorological models have different scales than hydrological land surface models, which hinders feedback analysis. Results from innovative field measurements (scintillometry) are presented that help integrate hydrology and meteorology by bridging this scale gap. Subsequently, the operationalization of the MM5 meteorological model is described. Numerical experimentation with MM5 shows that changes in land surface properties do have large feedback effects on regional circulation patterns.
Effects of charcoal production on maize yield, chemical properties and texture of soil
(Biology and Fertility of soils (Springer-Verlag), 2004-03) Oguntunde, Philip G.; Fosu, Matthias; Ajayi, Ayodele E.; Van de Giesen, Nick
The effects of charcoal production on soil textural and chemical properties were investigated in Ejura, Ghana. The aim was to study the effects of heating and charcoal residue on maize yield, soil texture and soil chemical properties. Composite samples were taken from the 0–10 cm layer of soil at charcoal-making sites and from adjacent fields (control). Twelve sites were randomly selected for the study across the range of the Kotokosu watershed. Maize was planted in four selected locations on charcoal site soils (CSS) and adjacent field soils (AFS) to assess the impact of charcoal production on crop yield. There was a significant increase in soil pH, base saturation, electrical conductivity, exchangeable Ca, Mg, K, Na and available P in the soil at the kiln sites as compared to the adjacent soils. A relative change of up to 329% was observed in K while organic C and total N decreased by 9.8% and 12.8%, respectively. Organic C and total N were highly correlated ( P <0.01) and both parameters significantly ( P <0.05) depended on clay minerals in the soils. Soil texture was also modified with a significantly higher sand content and lower clay fraction in the CSS. The grain and biomass yield of maize increased by 91% and 44%, respectively, on CSS as compared to AFS. Further research to ascertain the longterm effects of charcoal production on the soil environment and the fertility of tropical soils is needed. Keywords Charcoal production · Soil heating · Soil fertility · Maize yield · Ghana
Effects of charcoal production on soil physical properties in Ghana
(WILEY‐VCH Verlag, 2008-08) Oguntunde, Philip G.; Abiodun, Babatunde J.; Ajayi, Ayodele E.; Van De Giesen, Nick
Charcoal production, widespread in Ghana like in other W African countries, is a major driver of land-cover change. Effects of charcoal production on soil physical, including hydrological, properties, were studied in the forest–savannah transition zone of Ghana. Core and composite samples from 12 randomly selected sites across the width of Kotokosu watershed were taken from 0–10 cm layer at charcoal-site soils and adjacent field soils (control). These were used to determine saturated hydraulic conductivity (Ksat), bulk density, total porosity, soil texture, and color. Infiltration rates, surface albedo, and soil-surface temperature were also measured on both sites. The results showed that the saturated hydraulic conductivity of soils under charcoal kilns increased significantly (p < 0.01) from 6.1 ± 2.0 cm h–1 to 11.4 ± 5.0 cm h–1, resulting to a relative increase of 88%. Soil color became darkened under charcoal kilns with hue, value, and chroma decreasing by 8%, 20%, and 20%, respectively. Bulk density on charcoal-site soils reduced by 9% compared to adjacent field soils. Total porosity increased from 45.7% on adjacent field soils to 50.6% on earth kilns. Surface albedo reduced by 37% on charcoal-site soils while soil-surface temperature increased up to 4°C on average. Higher infiltration rates were measured on charcoal-site soils, which suggest a possible decrease in overland flow and less erosion on those kiln sites. Keywords: charcoal production / soil physical properties / Ksat / infiltration rates / reflection coefficient / watershed hydrology
Hydrotope-based protocol to determine average soil moisture over large areas for satellite calibration and validation with results from an observation campaign in the Volta
(IEEE, 2008-05-16) Friesen, Jan; Rodgers, Charles; Oguntunde, Philip G.; Hendrickx, Jan M.H.; Giesen, Nick van de
In West Africa, which is an extremely moisturelimited region, soil water information plays a vital role in hydrologic and meteorologic modeling for improved water resource planning and food security. Recent and upcoming satellite missions, such as SMOS and MetOp, hold promise for the regional observation of soil moisture. The resolution of the satellites is relatively coarse (> 100 km2 ), which brings with it the need for large-scale soil moisture information for calibration and validation purposes. We put forward a soil moisture sampling protocol based on hydrotopes. Hydrotopes are defined as landscape units that show internally consistent hydrologic behavior. This hydrotope analysis helps in the following ways: 1) by ensuring statistically reliable validation via the reduction of the overall pixel variance and 2) by improving sampling schemes for ground truthing by reducing the chance of sampling bias. As a sample application, we present data from three locations with different moisture regimes within the Volta Basin during both dry and wet periods. Results show that different levels of reduction in the overall pixel variance of soil moisture are obtained, depending on the general moisture status. With respect to the distinction between the different hydrotope units, it is shown that under intermediate moisture conditions, the distinction between the different hydrotope units is highest, whereas extremely dry or wet conditions tend to have a homogenizing effect on the spatial soil moisture distribution. This paper confirms that well-defined hydrotope units yield an improvement at pixel-scale soil moisture averages that can easily be applied.
Influence of climatic variables on whole-plant water use of cocoa under limited soil moisture condition
(Journal of Agriculture and Ecology Research International, 2019-10-21) Omotayo, Femi S.; Oguntunde, Philip G.; Olufayo, Ayorinde A.
Cocoa (Theobroma cacao L.) is a cash crop that is cultivated in many tropical regions of the world and is highly productive under favourable climatic conditions. Cocao, being originally an under storey tree of rainforests in tropical America, is traditionally cultivated below the canopy of shade trees. This study is carried out to establish the influence of climatic variables on whole-plant water use of cocoa under limited soil moisture conditions. An experimental plot was made in an even – aged 54 years old cocoa plantation which was demarcated while Water use measurement carried out for 20 consecutive days at the center of the cocoa plantation field at the Federal University of Technology, Akure using the temperature difference method (Sap flow meter). The results of evaporation rate and water consumed by crops led to decrease in soil water in the monitored root zone from 0.049 to 0.015 m3 m-3. Solar radiation reached a high value of 1002.37 Wm-2, with day time average of 238.02 Wm-2. Temperature ranges between 16.41 and 34.19ºC with a daily average of about 24.39ºC. Relative humidity varied from 98.60% to less than 32.37% with daily mean of around 74.90%. Vapour pressure varied from 0.01 to 2.87 kpa. The day time wind speeds rarely exceed 5.2 ms-1 while the daily averages were generally around 1.09 ms-1. The results also show that transpiration, (Ec) is mostly influenced by solar radiation with a correlation coefficient of 0.71 while other variable like temperature, Vapour pressure deficit, and Relative humidity has correlation coefficient of 0.62, 0.50 and 0.58 respectively. The total amount of rainfall during the experiment was 38.9 mm. This shows that solar radiation has greater influence on the transpiration of the cocoa plant than other variables in the study area
Influence of Tree Age and Variety on Allometric Characteristics and Water Use of Mangifera indica L. Growing in Plantation
(Hindawi Publishing Corporation, 2011-09-22) Oguntunde, Philip G.; Fasinmirin, Johnson T.; Van de Giesen, Nick
Mango (Mangifera indica L.), a diffuse-porous species and one of the most important tropical tree crops [1], belongs to the family Anacardiaceae [2]. It is believed that mango was brought from Arabia to Africa in the first millennium AD [3]. Ghana received more than a dozen cultivars in the early 1920s and more than a dozen other cultivars were brought in later from Florida and India [2]. However, because of identification problems, an effort was initiated in 1967 to classify the seedlings in the Ejura district, the Ejura Agricultural Station, and the plantation of the Faculty of Agriculture, University of Science and Technology, Kumasi, in order to eliminate confusions and have identifiable cultivars marked for future research. There is great potential for the rapid growth of mango industry in West Africa if the current planting rate and government encouragements are sustained. Although mango is drought tolerant and could be conveniently cropped under rain-fed conditions, supplemental irrigation may be required for optimising growth, fruit set, and yield [4]. Poor and unreliable flowering is one of the factors leading to low productivity [5], but applying irrigation from peak flowering to fruit maturity could induce reliable flowering leading to high yield [6, 7]. Preflowering irrigation was reported to increase the overall photosynthetic activity of the tree at the time of flowering [8]. The necessity to directly and continuously monitor water use for precise irrigation scheduling in mango plantations has been reported [4, 7]. Subsequently, a Granier sap flow measurement method was evaluated and applied successfully to measure sap flow per unit sapwood area in young to mature mango trees. Despite current advances, especially in Australia, there is little or no information regarding water use of mango trees in West Africa. In the study area, the planting practices have resulted in age differences of adjacent plantations coupled with indiscriminate mixtures of varieties or cultivars. These lead to differences in cultivars composition on different stands. Previous studies reported that young/mature trees use more water per unit sapwood area than old trees of the same species in a similar environment due to changes in stem and branch hydraulics with age [9, 10] as well as pressure gradient due to gravity [11]. The objectives of this study were 2 Journal of Botany to examine the degree to which differences in tree age and variety mixture affect water use and allometric characteristics of mango trees under subhumid tropical environment of West Africa. The study was part of the just concluded GLOWA Volta project (http://www.glowa-volta.de/), which lasted between 2000 and 2009. In the context of this project, designed to study “sustainable water use under various land use change and rainfall reliability,” understanding the hydrological process in the basin water balance is very important. Determinations of water use from each component of ecosystem vegetation were required and therefore partly motivated this study
Rainfall trends in Nigeria, 1901–2000
(Elsevier (Journal of Hydrology), 2011-12-09) Oguntunde, Philip G.; Abiodun, Babatunde J.; Lischeid, Gunnar
There is the need to evaluate changes in the spatial and temporal patterns of rainfall in order to improve water management strategies of a given region. In this study, standard tests are used to examine the existence of trend in annual and monthly rainfall of Nigeria over the last century. Rainfall variability index was estimated as standardized rainfall departure while autocorrelation spectral analysis is used to obtain the periodicities inherent therein. Rainfall spatial distribution was highly latitudinal dependent (r2 > 0.90) and had no clearly linear relations with the longitude. Rainfall variability index showed that 1950s was the wettest decade (+0.84) while 1980s was the driest (−1.19), with the two decades between 1970 and 1990 being drier than any other comparable period in the last century. Observed rainfall changes varied between −3.46 and +0.76 mm yr−2. About 90% of the entire landscape exhibited negative trends but only 22% showed significant changes at 5% level. There was a sharp difference between changes in rainfalls in 1931–1960 and 1961–1990 periods. Annual precipitation reduced by 7% between the two periods. While more than 90% of the landscape showed no significant rainfall change in the first period, about 57% of Nigeria showed a significant (P < 0.05) decrease in the second. The dominant peaks can be classified into four distinct rainfall cycles with periods 2–3, 5–7, 10–15 and 30 yr. These cycles may be associated with the stratospheric Quasi-Biennial Oscillation (QBO), the El-Nino Southern Oscillation (ENSO); the sunspot cycles and the Atlantic Multi-Decadal Oscillation (AMO) sea surface temperature, respectively.
Simulating the impacts of tree, C3, and C4 plant functional types on the future climate of West Africa
(MDPI, 2018-05-02) Olusegun, Christiana Funmilola; Oguntunde, Philip G.; Gbobaniyi, Emiola O.
This study investigates the future climatic impacts of different percentages of trees/shrubs, C4 and C3 plant functional types (PFTs) over the West Africa region. The ratio of co-existence among the different PFTs was done as a representation of agri-silviculture practices over the region. Nine sensitivity experiments of different percentages of trees/shrubs, and C4 and C3 PFTs were carried out with a regional climate model (RegCM4) driven by Global Climate Model (HADGEM2-ES) outputs. These experiments were carried out along the Guinea Savana zone of West Africa using both prescribed and dynamic vegetation options of the model. The model simulated the seasonal evolution of precipitation and temperature fields quite well, with correlations greater than 0.8, but exhibited cold and wet biases of about 1–2 °C and 1–4 mm/day, respectively. Widespread warming (1–3 °C) and drying (1–2 mm/day) is projected in the near future across most parts of West Africa all year round. The West African future climate change associated with the different percentages of trees/shrubs, and C4 and C3 PFTs varied with the vegetation state (prescribed or dynamic) and model domain sizes. The prescribed vegetation experiments induced cooling of about 0.5–2 °C in most areas along the designated agri-silviculture zone, except Liberia and Sierra Leone. Similarly, enhanced precipitation occurred over most parts of Ghana and coastal parts of Nigeria (0.5–3 mm/day). On the other hand, the dynamic vegetation option did not exhibit pronounced changes in temperature and precipitation, except with a larger domain size. This study suggests the implementation of agri-silviculture as a mitigation and adaptation land-use practice across West Africa if drought-tolerant crops and the deciduous trees are adopted.

Browsing by Author "Oguntunde, Philip G."

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