ResearchSpace :: Browsing by Author "Kapangaziwiri, Evison"

Browsing by Author "Kapangaziwiri, Evison"

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Application of the rainfall infiltration breakthrough (RIB) model for groundwater recharge estimation in west coastal South Africa
(Water Research Commission, 2013-04) Sun, X; Xu, Y; Jovanovic, Nebojsa; Kapangaziwiri, Evison; Brendonck, L; Bugan, Richard DH
Recharge estimation in arid and semi-arid areas is very challenging. The chloride mass balance method applied in western South Africa fails to provide reliable recharge estimates near coastal areas. A relationship between rainfall events and water level fluctuations (WLF) on a monthly basis was proposed in the rainfall infiltration breakthrough (RIB) model for the purpose of groundwater recharge estimation. In this paper, the physical meaning of parameters in the CRD and previous RIB models is clarified, and the RIB model is reviewed with the algorithm improved to accommodate various time scales, namely, daily, monthly and annual scales. Recharge estimates on a daily and monthly basis using the revised RIB approach in 2 study areas, one in a sandy alluvial aquifer (Riverlands) and the other in the Table Mountain Group (TMG) shallow unconfined aquifer (Oudebosch), are presented, followed by sensitivity analysis. Correlation analysis between rainfall and observed WLF data at daily scale and monthly scale, together with recharge estimates obtained from other methods, demonstrates that the RIB results using monthly data are more realistic than those for daily data, when using long time series. Scenarios using the data from Oudebosch with different rainfall and groundwater abstraction inputs are simulated to explore individual effects on water levels as well as recharge rate estimated on a daily basis. The sensitivity analysis showed that the recharge rate by the RIB model is specifically sensitive to the parameter of specific yield; therefore, the accurate representative specific yield of the aquifer needs to be selected with caution. The RIB model demonstrated in these two cases can be used to estimate groundwater recharge with sufficiently long time series of groundwater level and rainfall available in similar regions. In summary, the RIB model is best suited for shallow unconfined aquifers with relatively lower transmissivity; the utility of the RIB model for application in different climatic areas under different hydrogeological conditions needs to be further explored.
Assessing the impact of global changes on the surface water resources of Southwestern Nigeria
(Taylor & Francis, also IAHS, 2015-12) Ayeni, AO; Kapangaziwiri, Evison; Soneye, ASO; Engelbrecht, FA
Understanding the relative impact of land use, land cover and climate change (LULCC) on basin runoff is necessary in assessing basin water stress. This assessment requires long-term observed rainfall time series and land-use/land-cover (LULC) spatial data. However, there are challenges with the availability of spatio-temporal data, particularly limited range of available historical hydro-meteorological measurements. In order to assess the likely water stress, the study used long-term (1961–2007) rainfall data to drive the Pitman monthly rainfall-runoff model to assess changes to the water resources of three selected basins in Nigeria—Asa, Ogun, and Owena. Three CGCMs—CSIRO Mark3.5, MIROC3.2-medres and UKMO-HadCM3 dynamically downscaled to a 60 km by 60 km grid using the Conformal-Cubic Atmospheric Model (C-CAM)—are used to simulate impacts of future climate changes on water resources. These three models were found suitable for simulating rainfall-runoff based on the insignificant differences of models’ mean with mean of observed rainfall and temperature for pre-2010 data compared to other downscaled C-CAM models (GFDL-CM2.0, GFDL-CM2.1, and ECHAM5/MPI-Ocean model). The model results show increases in the runoff coefficient with decreases in forest cover between 1981 and 2007 with average runoff coefficients of 5.3%, 12.0% and 6.4% for Asa, Ogun and Owena basins respectively. Based on CSIRO, MIROC, and UKMO predicted annual reduction in rainfall trend, the future scenarios revealed a low runoff coefficient for the three basins—Asa (CSIRO 6.0%, MIROC 6.0%, and UKMO 5.9%), Ogun (CSIRO14.6%, MIROC 14.6%, and UKMO 14.4%), and Owena (CSIRO 8.5%, MIROC 8.7%, and UKMO 8.9%). In all scenarios Asa basin has lower runoff coefficient when compared to Ogun and Owena basins, indicating that future water stress in Asa basin would be much higher.
Assessing the impact of global changes on the surface water resources of Southwestern Nigeria
(Taylor & Francis, 2014-12) Ayeni, AO; Kapangaziwiri, Evison; Soneye, ASO; Engelbrecht, FA
Understanding the relative impact of land use, land cover and climate change (LULCC) on basin runoff is necessary in assessing basin water stress. This assessment requires long-term observed rainfall time series and land-use/land-cover (LULC) spatial data. However, there are challenges with the availability of spatio-temporal data, particularly limited range of available historical hydro-meteorological measurements. In order to assess the likely water stress, the study used long-term (1961–2007) rainfall data to drive the Pitman monthly rainfall-runoff model to assess changes to the water resources of three selected basins in Nigeria—Asa, Ogun, and Owena. Three CGCMs—CSIRO Mark3.5, MIROC3.2-medres and UKMO-HadCM3 dynamically downscaled to a 60 km by 60 km grid using the Conformal-Cubic Atmospheric Model (C-CAM)—are used to simulate impacts of future climate changes on water resources. These three models were found suitable for simulating rainfall-runoff based on the insignificant differences of models’ mean with mean of observed rainfall and temperature for pre-2010 data compared to other downscaled C-CAM models (GFDL-CM2.0, GFDL-CM2.1, and ECHAM5/MPI-Ocean model). The model results show increases in the runoff coefficient with decreases in forest cover between 1981 and 2007 with average runoff coefficients of 5.3%, 12.0% and 6.4% for Asa, Ogun and Owena basins respectively. Based on CSIRO, MIROC, and UKMO predicted annual reduction in rainfall trend, the future scenarios revealed a low runoff coefficient for the three basins—Asa (CSIRO 6.0%, MIROC 6.0%, and UKMO 5.9%), Ogun (CSIRO14.6%, MIROC 14.6%, and UKMO 14.4%), and Owena (CSIRO 8.5%, MIROC 8.7%, and UKMO 8.9%). In all scenarios Asa basin has lower runoff coefficient when compared to Ogun and Owena basins, indicating that future water stress in Asa basin would be much higher.
Assessing water resources availability in headwater sub-catchments of Pungwe River Basin in a changing climate
(2021-06) Gumbo, AD; Kapangaziwiri, Evison; Chikoore, H; Pienaar, Harrison H
Study Region: The Pungwe River Basin, which is predominantly rural, is a transboundary river shared between Zimbabwe and Mozambique. The riparian communities along the river largely depend on the availability of streamflow for their livelihoods which are now being threatened by the effects of a changing climate. Study focus: The study assessed the effects of climate change on water resources availability in 10 selected headwater sub-catchments of the Pungwe River Basin using the Pitman hydrological model. The model was driven by 10 statistically downscaled climate models forced with RCP 4.5 and RCP 8.5 for the near (2020–2060) and far (2061–2099) futures. New Hydrological Insights for the Region: The results of water resources availability varied, depending on whether the short- or long-term scenarios were modelled. 70 % of the sub-catchments predicted an increase in stream flow for the near- and far-future under the RCP 4.5 emission scenario. Under the RCP 8.5 scenario, a decrease in streamflow was simulated for all sub-catchments with the decrease ranging from -4.17 % to -71.69 %. The reduction in water resources would be significant in the drier parts of the basin than in the wetter parts, which are projected to maintain approximately 90 % of current streamflow levels. Given the uncertainty in future climate simulations, it is prudent that both scenarios be regarded as probabilities. Thus, effective adaptive basin management should consider both.
Assessment of satellite-derived rainfall and its use in the ACRU agro-hydrological model
(2020-11) Suleman, Shuaib; Chetty, KT; Clark, DJ; Kapangaziwiri, Evison
Unfortunately, for various reasons, in-situ rain gauge networks are diminishing, especially in southern Africa, resulting in sparse networks whose records give a poor representation of rainfall occurrence, patterns andmagnitudes. Hydrological models are used to inform decision making; however, model performance is directly linked to the quality of input data, such as rainfall. Therefore, the use of satellite-derived rainfall is being increasingly advocated as a viable alternative or supplement. The aim of this study was to evaluate the representativeness of satellite-derived rainfall and its utility in the ACRU agro-hydrological model to simulate streamflow magnitudes, distributions and patterns. The satellite-derived rainfall products selected for use in this study were TRMM3B42, FEWSARC2.0, FEWSRFE2.0, TAMSAT 3.0 and GPM-IMERG4. The satellite rainfall products were validated against available historical observed records and then were used to drive simulations using the ACRU agro-hydrological model in the upper uMngeni, upper uThukela and upper and central Breede catchments in South Africa. At the daily timescale, satellite-derived and observed rainfall were poorly correlated and variable among locations. However, monthly, seasonal and yearly rainfall totals and simulated streamflow volumes were in closer agreement with historical observations than the daily correlations; more so in the upper uMngeni and uThukela than in the upper and central Breede (e.g. FEWSARC2.0 and FEWSRFE2.0, producing relative volume errors of 3.18%, 4.63%, -5.07% and 2.54%, 9.54%, -1.67%, respectively, at Gauges V2E002, 0268883 and 02396985). Therefore, the satellite-derived rainfall shows promise for use in applications operating at coarser temporal scales than at finer daily ones. Complex topographical rainfall generation and varying weather systems, e.g. frontal rainfall, affected the accuracy of satellite-derived product estimates. This study focused on utilising the wealth of available raw satellite data; however, it is clear that the raw satellite data need to be corrected for bias and/or downscaled to provide more accurate results.
The delineation of alluvial aquifers towards a better understanding of channel transmission losses in the Limpopo River Basin
(Elsevier, 2018-12) Mvandaba, Vuyelwa; Hughes, D; Kapangaziwiri, Evison; Mwenge Kahinda, Jean-Marc; Hobbs, Philip J; Madonsela, Sabelo; Oosthuizen, Nadia
Understanding the impact of key hydrological processes on the availability of water resources is an integral component of equitable and sustainable integrated water resource management. Previous hydrological studies conducted in the Limpopo River Basin have revealed a gap in the understanding of surface water-groundwater interactions, particularly channel transmission loss processes. These studies, focused largely on the Limpopo River’s main stem, have attributed the existence of these streamflow losses to the presence of significant alluvial aquifers and indicated that the losses account for about 30 percent (or 1000 Mm3 a-1) of the basin’s water balance. This paper reports on the delineation of alluvial aquifers across the Luvuvhu sub-basin using Landsat-8 imagery and the estimation of potential transmission losses based on the aquifer properties. To delineate alluvial aquifers, general land cover classes including alluvial aquifers were produced from Landsat-8 imagery through image classification. The areal extent of the delineated alluvial aquifers was calculated using ArcMap 10.3 Results indicate that the alluvial aquifers occur as relatively narrow channel alluvial deposits (32-124 m in width) and extensive vegetated floodplain deposits. In the Luvuvhu sub-basin, these are mostly located along the lower reach of the 200 km long meandering Luvuvhu River. The outcome of the delineation of the alluvial aquifer is seen to be consistent with existing regional hydrogeological maps. Based on the characteristics and size of the aquifer it is estimated that the capacity of the aquifer is approximately 9.34 Mm3, which could be ‘lost’ from the Luvuvhu River system at any given point in time. The actual transmission losses however depend on a number of factors including the level of flow, the size of the aquifer in contact with the riverbed, regional slope for water loss into the adjacent areas, antecedent moisture content of the aquifer and riparian evapotranspiration.
Evaluation of recent hydro-climatic changes in four tributaries of the Niger River Basin (West Africa)
(Taylor & Francis, 2017-10) Badou, DF; Kapangaziwiri, Evison; Diekkrüger, B; Hounkpè, J; Afouda, A
West Africa experienced severe drought during the 1970s and 1980s, posing a threat to water resources. A wetter climate more recently suggests recovery from the drought. The Mann-Kendall trend and Theil-Sen’s slope estimator were applied to detect probable trends in weather elements in four sub-basins of the Niger River Basin between 1970 and 2010. The cross-entropy method was used to detect breakpoints in rainfall and runoff, Spearman’s rank test for correlation between the two, and cross- correlation analysis for possible lags. Results showed an overall increase in rainfall and runoff and a decrease in sunshine duration. Spearman’s coefficients suggest significant (5%) moderate to strong rainfall–runoff correlation for three sub-basins. A significant lower runoff was observed around 1979, with a rainfall break around 1992, indicating possible cessation of the drought. Temperatures increased significantly, at 0.02–0.05°C year-1, with a negative wind speed trend for most stations. Half of the stations exhibited an increase in potential evapotranspiration.
The fate of the City of Mutare's urban water supply as changing climate impacts on its source in the Pungwe sub-catchment
(2021-10) Gumbo, AD; Kapangaziwiri, Evison
Sustaining a steady supply of water to urban communities is of importance in a period that is characterised by rapid urban population growth, a global pandemic, and a changing climate that threatens the availability of the resource from its sources. Water supply to the City of Mutare is from three sources, Small Bridge Dam, Odzani, and the Pungwe River. The Pungwe source provides better quality water resources equivalent to the combined quantity supplied by the other two. It becomes an important source for the city, but climate change threatens the availability of water resources in the southern African region. Thus, it is imperative to quantitatively assess the impacts of a changing climate on water resources to enable the development of sustainable management alternatives. Using two carbon emission scenarios Representative Concentration Pathways (RCPs) 4.5 and 8.5, the study assesses the future availability of water resources from the Pungwe River to the City of Mutare using the Pitman hydrological model applied in an uncertainty framework. Available historical streamflow observations at gauging station F14 indicate a Q95 flow of about 2 Mm3/year. Projected future water resources at the end of the 21st century show a slight increase of up to 2.38% under the low carbon emission scenario (RCP4.5) and a decrease of up to 9.73%under the high carbon emission scenario (RCP8.5). These model-generated results are useful to water managers to plan for catchment management strategies that would ensure continuous urban water supply, and the identification and development of possible future alternative water sources.
Hydrological assessment of freshwater resource areas in the Zambezi River Basin
(2012-10) Mwenge Kahinda, Jean-Marc; Kapangaziwiri, Evison
Hydrological modelling of the Zambezi River Basin will inform the development and formulation of appropriate management strategies to ensure and maintain environmental flow requirements.
Hydrological characterisation of wetlands: Understanding wetlands-catchment linkages
(2015-10) Mandlazi, Nompumelelo P; Kapangaziwiri, Evison; Mwenge Kahinda, Jean-Marc; Mazvimavi, D
This paper aims to assess the performance of two hydrological models routinely used in South Africa with the wetlands processes included.
The impacts of commercial plantation forests on groundwater recharge: A case study from George (Western Cape, South Africa)
(Elsevier, 2019-08) Tuswa, N; Bugan, Richard DH; Mapeto, T; Jovanovic, Nebojsa; Gush, Mark B; Kapangaziwiri, Evison; Dzikiti, Sebinasi; Kanyerere, T; Xu, Y
The benefits of the commercial plantation forestry sector (income generation and job provision) come at considerable environmental costs, particularly the impact of the industry on water resources. Plantation forests exhibit higher evapotranspiration rates compared to indigenous forests/grasslands. A reduction of the water yield in a catchment is one of the most frequently reported impacts of afforestation. Afforestation also significantly impacts groundwater, which is becoming an increasingly important resource for water supply in South Africa. Very few studies have however quantified in detail the impact of different commercial forests grown in South Africa on groundwater and the interactions with surface water. This study sought to contribute to addressing this important knowledge gap. The main objective was to compare groundwater recharge dynamics in commercial plantation forests and co-occurring indigenous forests. The HYDRUS-2D model was used to simulate the hillslope hydrological dynamics along 3 study transects, i.e. a Pinus radiata transect, a Pinus elliotii transect and in the Groenkop indigenous forest, during the period 1 October 2016 to 30 September 2017. The model was used to simulate the interaction between the vegetation, unsaturated zone and the saturated zone in order to better understand the groundwater recharge dynamics along each transect. As a precursor to model application a detailed conceptual model of the recharge processes occurring in the study areas was developed. The model considered the prevailing geomorphological and hydrogeological conditions. HYDRUS-2D was able to adequately simulate the soil hydraulic properties and vegetation water use characterizing the study transects. The hydrological dynamics of the simulation results also conform to the conceptual understanding of groundwater recharge processes evident in the study area. Over the entire simulation period (365 days), fluxes which left the Pinus elliotii, Pinus radiata and Groenkop forest model domains via the lower boundary amounted to 36 mm, 14 mm and 169 mm respectively. The total drainage observed at the three transects was largely influenced by the evapotranspiration losses. Rainfall intensity and frequency was observed to be a driving variable for the occurrence of deep drainage. The groundwater recharge dynamics observed during this study conforms to the notion that groundwater recharge is driven by single or multiple events and not by annual averages. The study has provided further evidence of increased transpiration rates associated with plantation forests when compared to indigenous forests. This in turn, has also resulted in reduced deep drainage and potential groundwater recharge. These results highlight the importance of accurately accounting for ET losses in groundwater recharge assessments and estimation techniques.
Implementing integrated catchment management in the Limpopo River Basin Phase 1: Situational assessment
(2012-10) Mwenge Kahinda, Jean-Marc; Kapangaziwiri, Evison; Engelbrecht, FA; Meissner, Richard; Ashton, PJ
A situational assessment of De Beers’ mining operations within a water-stressed area, and close to an ecologically sensitive area, offers useful insights for the development of specific interventions in the areas surrounding their mining operations. This also holds implications for the specific mine’s sustainability.
Investigation on the 1970s and 1980s droughts in four tributaries of the Niger River Basin (West Africa).
(Curran Associates, 2015-07) Badou, DF; Afouda, A; Diekkruger, B; Kapangaziwiri, Evison
West Africa has experienced severe droughts during 1970s and 1980s. On the other hand, the region is characterized by high inter-annual rainfall variability and there seems to be a recent recovery. But has the drought stopped? To answer this question, we evaluated spatio-temporal pattern of rainfall and runoff in four tributaries (Sota, Alibori, Mekrou and Kompa-gorou) of the Niger River basin, covering a total area of 40,000km2 for the period 1971 to 2010. First, decadal rainfall variability was investigated using Kriging-based isohyets. Cross entropy method was then applied to detect breakpoints in rainfall and runoff series. Additionally, the rainfall-runoff relationship was assessed via Spearman's rank correlation coefficients. Yet the drought started in 1970s peaked in 1980s, but the wetness of the last two decades led to an overall increase of both rainfall and runoff over the study area. Though a moderate to strong (0.57-0.66) rainfallrunoff correlation was obtained for three of the four investigated catchments, the breakpoints in rainfall and runoff series were not per se consistent probably due to gaps in discharge data. Rainfall depicted a shift around 1992 but runoff around 1983. The wetness of the decades, 1990s and 2000s and the manifold floods records of this first half of 2010s over West Africa are evidences that the droughts of 1970s and 1980s have stopped.
Modelling blue and green water availability under climate change in the Beninese Basin of the Niger River Basin, West Africa
(Wiley, 2018-05) Badou, DF; Diekkrüger, B; Kapangaziwiri, Evison; Mbaye, ML; Yira, Y; Lawin, AE; Oyerinde, GT; Afpouda, A
The aim of this study was to quantify climate change impact on future blue water (BW) and green water (GW) resources as well as the associated uncertainties for four sub-basins of the Beninese part of the Niger River Basin. The outputs of three regional climate models (HIRHAM5, RCSM, and RCA4) under two emission scenarios (RCP4.5 and RCP8.5) were downscaled for the historical period (1976-2005) and for the future (2021-2050) using the Statistical DownScaling Model (SDSM). Comparison of climate variables between these two periods suggests that rainfall will increase (1.7 to 23.4%) for HIRHAM5 and RCSM under both RCPs but shows mixed trends (-8.5 to 17.3%) for RCA4. Mean temperature will also increase up to 0.48°C for HIRHAM5 and RCSM but decrease for RCA4 up to -0.37°C. Driven by the downscaled climate data, future BW and GW were evaluated with hydrological models validated with streamflow and soil moisture, respectively. The results indicate that GW will increase in all the four investigated sub-basins while BW will only increase in one sub-basin. The overall uncertainty associated with the evaluation of the future BW and GW was quantified through the computation of the inter-quartile range of the total number of model realizations (combinations of regional climate models and selected hydrological models) for each sub-basin. The results show larger uncertainty for the quantification of BW than GW. To cope with the projected decrease in BW that could adversely impact the livelihoods and food security of the local population, recommendations for the development of adequate adaptation strategies are briefly discussed.
Modelling of channel transmission loss processes in semi-arid catchments of southern Africa using the Pitman Model
(Copernicus Publications, 2018-05) Mvandaba, Vuyelwa; Hughes, D; Kapangaziwiri, Evison; Mwenge Kahinda, Jean-Marc; Oosthuizen, Nadia
Water availability is one of the major societal issues facing the world. The ability to understand and quantify the impact of key hydrological processes, on the availability of water resources, is therefore integral to ensuring equitable and sustainable resource management. Channel transmission losses are an “under-researched” hydrological process that affects resource availability in many semi-arid regions such as the Limpopo River Basin in southern Africa, where the loss processes amount to approximately 30% of the water balance. To improve the understanding of these loss processes and test the capability of modelling routines, three approaches using the Pitman model are applied to selected alluvial aquifer environments. The three approaches are an explicit transmission loss function, the use of a wetland function to represent channel-floodplain storage exchanges and the use of a “dummy” reservoir to represent floodplain storage and evapotranspiration losses. Results indicate that all three approaches are able to simulate channel transmission losses with differing impacts on the regional flows. A determination of which method best represents the channel transmission losses process requires further testing in a study area that has reliable observed historical records.
Natural hazards in a changing world: a case for ecosystem-based management
(Public Library of Science, 2014-05) Nel, JL; Le Maitre, David C; Nel, DC; Reyers, B; Archibald, S; Van Wilgen, BW; Forsyth, GG; Theron, AK; O'Farrell, Patrick J; Mwenge Kahinda, Jean-Marc; Engelbrecht, FA; Kapangaziwiri, Evison; Van Niekerk, Lara; Barwell, L
Communities worldwide are increasingly affected by natural hazards such as floods, droughts, wildfires and storm-waves. However, the causes of these increases remain underexplored, often attributed to climate changes or changes in the patterns of human exposure. This paper aims to quantify the effect of climate change, as well as land cover change, on a suite of natural hazards. Changes to four natural hazards (floods, droughts, wildfires and storm-waves) were investigated through scenario-based models using land cover and climate change drivers as inputs. Findings showed that human induced land cover changes are likely to increase natural hazards, in some cases quite substantially. Of the drivers explored, the uncontrolled spread of invasive alien trees was estimated to halve the monthly flows experienced during extremely dry periods, and also to double fire intensities. Changes to plantation forestry management shifted the 1:100 year flood event to a 1:80 year return period in the most extreme scenario. Severe 1:100 year storm-waves were estimated to occur on an annual basis with only modest human-induced coastal hardening, predominantly from removal of coastal foredunes and infrastructure development. This study suggests that through appropriate land use management (e.g. clearing invasive alien trees, re-vegetating clear-felled forests, and restoring coastal foredunes), it would be possible to reduce the impacts of natural hazards to a large degree. It also highlights the value of intact and well-managed landscapes and their role in reducing the probabilities and impacts of extreme climate events.
Parameter and input data uncertainty estimation for the assessment of water resources in two sub-basins of the Limpopo River Basin
(Copernicus Publications, 2017-07) Oosthuizen, Nadia; Hughes, DA; Kapangaziwiri, Evison; Mwenge Kahinda, Jean-Marc; Mvandaba, Vuyelwa
The demand for water resources is rapidly growing, placing more strain on access to water and its management. In order to appropriately manage water resources, there is a need to accurately quantify available water resources. Unfortunately, the data required for such assessment are frequently far from sufficient in terms of availability and quality, especially in southern Africa. In this study, the water resources of two sub-basins of the Limpopo River Basin – the Mogalakwena in South Africa and the Shashe shared between Botswana and Zimbabwe – are estimated using a hydrological model. A model is a simplification of an entity of the real world and is thus inevitably an imperfect approximation of a complex reality. In southern Africa water use data are among the most unreliable sources of data because available databases generally consist of licensed information and use is generally unknown. Therefore, model parameter estimation and input data are significant sources of uncertainty that should be quantified. Thus, the study assesses how uncertainties in model parameterisation and model input data affects the estimation of surface water resources of the sub-basins. Farm reservoirs and irrigated areas data from various sources were collected and used to run the model. Results indicate that the total model output uncertainty is higher for the Shashe sub-basin which is more data scarce than the Mogalakwena sub-basin. The study illustrates the importance of including uncertainty in the water resources assessment process to provide baseline data for decision making in resource management and planning.
Quantification of water resources uncertainties in the Luvuvhu sub-basin of the Limpopo river basin
(Elsevier, 2018-06) Oosthuizen, Nadia; Hughes, D; Kapangaziwiri, Evison; Mwenge Kahinda, Jean-Marc; Mvandaba, Vuyelwa
In the absence of historical observed data, models are generally used to describe the different hydrological processes and generate data and information that will inform management and policy decision making. Ideally, any hydrological model should be based on a sound conceptual understanding of the processes in the basin and be backed by quantitative information for the parameterization of the model. However, these data are often inadequate in many sub-basins, necessitating the incorporation of the uncertainty related to the estimation process. This paper reports on the impact of the uncertainty related to the parameterization of the Pitman monthly model and water use data on the estimates of the water resources of the Luvuvhu, a sub-basin of the Limpopo river basin. The study reviews existing information sources associated with the quantification of water balance components and gives an update of water resources of the sub-basin. The flows generated by the model at the outlet of the basin were between 44.03Mm(sup)3 and 45.48Mm(sup)3 per month when incorporating +\-20% uncertainty to the main physical runoff generating parameters. The total predictive uncertainty of the model increased when water use data such as small farm and large reservoirs and irrigation were included. The dam capacity data was considered at an average of 62% uncertainty mainly as a result of the large differences between the available information in the national water resources database and that digitised from satellite imagery. Water used by irrigated crops was estimated with an average of about 50% uncertainty. The mean simulated monthly flows were between 38.57 Mm(sup)3 and 54.83Mm(sup)3 after the water use uncertainty was added. However, it is expected that the uncertainty could be reduced by using higher resolution remote sensing imagery.
The role of basin physical property data in assessing water stress in water resources studies: The application of the Pitman Rainfall-runoff model in Nigeria
(2012-11) Ayeni, AO; Kapangaziwiri, Evison
This paper examines the role played by basin physical attributes in determining river runoff. The approach uses soil and other available hydro-meteorological and geophysical information to directly estimate the parameters of the Pitman rainfall-runoff model to generate time series of historical and future hydrology of the basin. This study discusses the physical property information required, which includes basin soil texture types, depths, soil hydraulic and drainage properties, topographic slope and sub-surface geological conditions. FAO and available Nigeria soil maps provided a baseline of the requisite general soil information and other soil attributes information was inferred from literature. Owena, Asa and Ogun basins were used as case studies to evaluate the parameter estimation routines and the Pitman rainfall-runoff monthly model in Nigeria. Owena basin has some historical data, and based on the experience of using the model gained in this basin the approaches were then transferred to the ungauged basins of Asa and Ogun. While relative success was achieved in generating the hydrology of the test basins, it is suggested that the uncertainty related to the parameter estimation and the rainfall input be investigated and incorporated into the estimation process to provide a range of probable basin hydrology.
Soil hydrological properties of a tropical basin: the case study of the Beninese part of the Niger River
(Dresden Nexus Conference: Water, Soil and Waste, 25-27 March 2015, Dresden, Germany, 2015-03) Badou, DF; Diekkrüger, B; Afouda, A; Kapangaziwiri, Evison; Hounkpe, J; Steup, G
Graduate Research Program on Climate Change and Water Resources, University of Abomey-Calavi, Abomey-Calavi, Benin Department of Geography, University of Bonn, Bonn, Germany Graduate Research Program on Climate Change and Water Resources, University of Abomey-Calavi, Abomey-Calavi, Benin CSIR. Natural Resources and the Environment Graduate Research Program on Climate Change and Water Resources, University of Abomey-Calavi, Abomey-Calavi, Benin Department of Geography, University of Bonn, Bonn, Germany

Browsing by Author "Kapangaziwiri, Evison"

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