Akpofure E. Taigbenu

Bio: Akpofure E. Taigbenu is an academic researcher from University of the Witwatersrand. The author has contributed to research in topics: Nonlinear system & Fundamental solution. The author has an hindex of 19, co-authored 69 publications receiving 1472 citations. Previous affiliations of Akpofure E. Taigbenu include Cornell University & National University of Science and Technology.

Domestic rainwater harvesting to improve water supply in rural South Africa

Abstract: Halving the proportion of people without sustainable access to safe drinking water and basic sanitation, is one of the targets of the 7th Millennium Development Goals (MDGs). In South Africa, with its mix of developed and developing regions, 9.7 million (20%) of the people do not have access to adequate water supply and 16 million (33%) lack proper sanitation services. Domestic Rainwater Harvesting (DRWH), which provides water directly to households enables a number of small-scale productive activities, has the potential to supply water even in rural and peri-urban areas that conventional technologies cannot supply. As part of the effort to achieve the MDGs, the South African government has committed itself to provide financial assistance to poor households for the capital cost of rainwater storage tanks and related works in the rural areas. Despite this financial assistance, the legal status of DRWH remains unclear and DRWH is in fact illegal by strict application of the water legislations. Beyond the cost of installation, maintenance and proper use of the DRWH system to ensure its sustainability, there is risk of waterborne diseases. This paper explores challenges to sustainable implementation of DRWH and proposes some interventions which the South African government could implement to overcome them.

Developing suitability maps for rainwater harvesting in South Africa

Abstract: Dry spells are a direct consequence of spatial and temporal variability of rainfall, and these jeopardise the success of rainfed agriculture by causing crop yield reduction and crop failure in rural South Africa. The potential of rainwater harvesting (RWH) to mitigate the spatial and temporal variability of rainfall has brought about its revival during the last two decades. For planning and implementation purposes, it is critical to be able to identify areas suitable for RWH. The paper presents a methodology that enable water managers to assess the suitability of RWH for any given area of South Africa. Previous methodologies developed to assess RWH suitability recognised the importance of the socio-economic factors but did not incorporate them in their assessment. This non-integration of socio-economic factors is pointed as the main cause of failure of rainwater harvesting projects. In this study, in-field RWH and ex-field RWH suitability maps are developed based on a combination of physical, ecological and socio-economic factors. Model Builder, an extension of ArcView 3.3 that enables a weighted overlay of datasets, is used to create the suitability model, comprising the physical, ecological and vulnerability sub-models from which the physical, the ecological and the vulnerability maps are derived respectively. Results indicate that about 30% is highly suitable for in-field RWH and 25% is highly suitable for ex-field RWH. Details of the proposed method as well as the suitability maps produced are presented in this paper. The implementation of this method is envisaged to support any policy shifts towards wide spread adoption of RWH.

The green element method

Abstract: This paper discusses an element-by-element approach of implementing the Boundary Element Method (BEM) which offers substantial savings in computing resource, enables handling of a wider range of problems including non-linear ones, and at the same time preserves the second-order accuracy associated with the method. Essentially, by this approach, herein called the Green Element Method (GEM), the singular integral theory of BEM is retained except that its implementation is carried out in a fashion similar to that of the Finite Element Method (FEM). Whereas the solution procedure of BEM couples the information of all nodes in the computational domain so that the global coefficient matrix is dense and full and as such difficult to invert, that of GEM, on the other hand, involves only nodes that share common elements so that the global coefficient matrix is sparse and banded and as such easy to invert. Thus, GEM has the advantage of being more computationally efficient than BEM. In addition, GEM makes the singular integral theory more flexible and versatile in the sense that GEM readily accommodates spatial variability of medium and flow parameters (e.g., flow in heterogeneous media), while other known numerical features of BEM—its second-order accuracy and ability to readily handle problems with singularities are retained by GEM. A number of schemes is incorporated into the basic Green element formulation and these schemes are examined with the goal of identifying optimum schemes of the formulation. These schemes include the use of linear and quadratic interpolation functions on triangular and rectangular elements. We found that linear elements offer acceptable accuracy and computational effort. Comparison of the modified fully implicit scheme against the generalized two-level scheme shows that the modified fully implicit scheme with weight of about 1·25 offers a marginally better approximation of the temporal derivative. The Newton–Raphson scheme is easily incoporated into GEM and provides excellent results for the time-dependent non-linear Boussinesq problem. Comparison of GEM with conventional BEM is done on various numerical examples, and it is observed that, for comparable accuracy, GEM uses less computing time. In fact, from the numerical simulations carried out, GEM uses between 15 and 45 per cent of the simulation time of BEM.

Domestic rainwater harvesting as an adaptation measure to climate change in South Africa

Abstract: Climate change is an additional threat that puts increased pressure on already stressed hydrological systems and water resources. The impacts of climate change are already visible given that temperature and rainfall variabilities have increased and intensified over the last two decades. Recent studies indicate the extreme vulnerability of Southern Africa to the impacts of climate change and recommend that appropriate adaptation measures be put in place. Rainwater harvesting (RWH) is listed among the specific adaptation measures that the water sector in Africa needs to undertake to cope with future climate change. At present, there is limited application of RWH, despite its high potential for alleviating the impacts of climate change on water security in many areas of Africa. The paper presents a methodology that enables water managers to incorporate the climate change component during the design phase of domestic RWH (DRWH) systems. The Roof model was used to calculate the optimum size of the RWH tank and appraise its water security (percentage of demand satisfied) under different scenarios (with and without climate change). Results indicate that the optimum RWH tank volume is 0.5 m 3 in the four quaternary catchments (QCs) studied with the humid QC, as expected, providing the highest water security of about 30%. On the basis of forecasted rainfall downscaled from six global circulation models, the ranges of water security attained by a 0.5 m 3 RWH tank are 10–15% in the arid QC, 15–20% in both the semi-arid and dry sub humid QCs and 30–40% in the humid QC. Furthermore, the high value of the water security climate induced index ( γ > 0.6) confirms the high susceptibility of South Africa to climate change and, therefore, the need for appropriate adaptation measures.

Rainwater harvesting to enhance water productivity of rainfed agriculture in the semi-arid Zimbabwe

Abstract: Zimbabwe’s poor are predominantly located in the semi-arid regions and rely on rainfed agriculture for their subsistence. Decline in productivity, scarcity of arable land, irrigation expansion limitations, erratic rainfall and frequent dry spells, among others cause food scarcity. The challenge faced by small-scale farmers is to enhance water productivity of rainfed agriculture by mitigating intra-seasonal dry spells (ISDS) through the adoption of new technologies such as rainwater harvesting (RWH). The paper analyses the agro-hydrological functions of RWH and assesses its impacts (at field scale) on the crop yield gap as well as the Transpirational Water Productivity (WPT). The survey in six districts of the semi-arid Zimbabwe suggests that three parameters (water source, primary use and storage capacity) can help differentiate storage-type-RWH systems from “conventional dams”. The Agricultural Production Simulator Model (APSIM) was used to simulate seven different treatments (Control, RWH, Manure, Manure + RWH, Inorganic Nitrogen and Inorganic Nitrogen + RWH) for 30 years on alfisol deep sand, assuming no fertiliser carry over effect from season to season. The combined use of inorganic fertiliser and RWH is the only treatment that closes the yield gap. Supplemental irrigation alone not only reduces the risks of complete crop failure (from 20% down to 7% on average) for all the treatments but also enhances WPT (from 1.75 kg m−3 up to 2.3 kg m−3 on average) by mitigating ISDS

Advanced Engineering Mathematics. By C. R. Wylie. Pp. xiv, 813. 1966. (McGraw-Hill.)

Abstract: Ordinary differential equations of the first order linear differential equations complex numbers and linear algebra simultaneous linear differential equations numerical methods the descriptive theory of nonlinear differential equations mechanical systems and electric circuits Fourier series Fourier integrals and Fourier transforms the Laplace transformation partial differential equations Bessel functions and Legendre polynomials applications and further properties of matrices vector analysis the calculus of variations analytic functions of a complex variable infinite series in the complex plane the theory of residues conformal mapping.

Phenotyping for drought tolerance of crops in the genomics era.

Abstract: Improving crops yield under water-limited conditions is the most daunting challenge faced by breeders. To this end, accurate, relevant phenotyping plays an increasingly pivotal role for the selection of drought-resilient genotypes and, more in general, for a meaningful dissection of the quantitative genetic landscape that underscores the adaptive response of crops to drought. A major and universally recognized obstacle to a more effective translation of the results produced by drought-related studies into improved cultivars is the difficulty in properly phenotyping in a high-throughput fashion in order to identify the quantitative trait loci that govern yield and related traits across different water regimes. This review provides basic principles and a broad set of references useful for the management of phenotyping practices for the study and genetic dissection of drought tolerance and, ultimately, for the release of drought-tolerant cultivars.

A Framework for Dealing With Uncertainty due to Model Structure Error

Abstract: Although uncertainty about structures of environmental models (conceptual uncertainty) is often acknowledged to be the main source of uncertainty in model predictions, it is rarely considered in environmental modelling. Rather, formal uncertainty analyses have traditionally focused on model parameters and input data as the principal source of uncertainty in model predictions. The traditional approach to model uncertainty analysis, which considers only a single conceptual model, may fail to adequately sample the relevant space of plausible conceptual models. As such, it is prone to modelling bias and underestimation of predictive uncertainty. In this paper we review a range of strategies for assessing structural uncertainties in models. The existing strategies fall into two categories depending on whether field data are available for the predicted variable of interest. To date, most research has focussed on situations where inferences on the accuracy of a model structure can be made directly on the basis of field data. This corresponds to a situation of ‘interpolation’. However, in many cases environmental models are used for ‘extrapolation’; that is, beyond the situation and the field data available for calibration. In the present paper, a framework is presented for assessing the predictive uncertainties of environmental models used for extrapolation. It involves the use of multiple conceptual models, assessment of their pedigree and reflection on the extent to which the sampled models adequately represent the space of plausible models. � 2005 Elsevier Ltd. All rights reserved.

Climate change and challenges of water and food security

Abstract: Water and food security are the key challenges under climate change as both are highly vulnerable to continuously changing climatic patterns. Studies have predicted that the average global temperature may increase by 1.4–5.8 °C and there would be substantial reduction in fresh water resources and agricultural yield by the end of the 21st century. Approximately 75% of the Himalayan glaciers are on retreat and will disappear by 2035. Moreover in Africa (Sub-Saharan Africa) by 2050 the rainfall could drop by 10%, which would reduce drainage by 17%. Majority of the fresh water resources has already been depleted and there is reduction in agricultural production globally with escalation in population and food demand. Some of the prominent climate change impacts are, growing deserts, and increase in the magnitude of floods and droughts. An extreme decline in crop yields in arid and semi arid areas globally has caused food shortages and a manifold increase in food inflation. Countries of Africa, Middle East, Arab and Asia have close economic ties with natural resource and climate-dependent sectors such as forestry, agriculture, water, and fisheries. This manuscript highlights groundwater recharge by utilization of wastewater using the Soil Aquifer Treatment (SAT) method in irrigation and the significance and methods of artificial recharge of groundwater. This paper also presents easily and economically feasible options to ensure water and food security under climate change and recommend formation of effective adaptation and mitigation polices and strategies to minimizing the impact of climate change on water resources and irrigation.