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Kowe P.,Geoinformation and Remote Sensing Institute | Pedzisai E.,Bindura University of Science Education | Gumindoga W.,University of Zimbabwe | Rwasoka D.T.,Upper Manyame Subcatchment Council
Geocarto International | Year: 2015

Changes in landscape composition and configuration patterns of Sancaktepe Municipal District in the Asian side of Istanbul Metropolitan City of Turkey were analysed using landscape metrics. Class-level and landscape-level metrics were calculated from the land cover/land use data using Patch Analyst, an extension in the Arc View GIS. The land cover/land use data were derived from classified satellite images of Landsat Thematic Mapper of 2002 and 2009 for Sancaktepe District. There was evidence of increase in agglomeration process of built-up patches as indicated by the increases in mean patch size, decrease in total edge and number of patches between 2002 and 2009. The urban expansion pattern experienced overall was not fragmented but concentrated due to infilling around existing patches. Changes in Area-Weighted Mean Shape Index and Area-Weighted Patch Fractal Dimension Index indicated that the physical shapes within built-up, forest and bareland areas were relatively complex and irregular. A conclusion is made in this study that spatial metrics are useful tools to describe the urban landscape composition and configuration in its various aspects and certain decisions whether to approve a specific development in urban planning could, for example, be based on some measures of urban growth form or pattern in terms of uniformity and irregularity, attributable to the dynamic processes of agglomeration and fragmentation of land cover/land use patches caused by urban expansion. © 2014, © 2014 Taylor & Francis. Source


Rwasoka D.T.,Upper Manyame Subcatchment Council | Madamombe C.E.,Digby Wells Environmental | Gumindoga W.,Box MP | Kabobah A.T.,University of Energy and Natural Resources
Physics and Chemistry of the Earth | Year: 2014

Hydrologic modelling lies at the core of hydrology and water resources management. Attempts at gaining a holistic grasp on model robustness, hydrologic theory and processes have inadvertently led to models that are not-well structured or too complex to apply in arid and semi-arid catchments and in Africa, in particular. In view of this, this paper reports on the application of a monthly parsimonious hydrologic model in two catchments in Zimbabwe, the Nyatsime and Upper Save river catchments. The two (2) parameter monthly parsimonious GR2M model was applied. The inputs were rainfall and potential evapotranspiration. Measured discharge was used for calibration and validation. Calibration and uncertainty analysis were done using the Differential Evolution Adaptive Metropolis (DREAM) algorithm. The performance of the GR2M model was evaluated using ten (10) model performance metrics. Parameter indentifiability was analysed on the basis of the shape of the posterior distribution of parameters. Parameter and total uncertainty were analysed in the context of the formal Bayesian DREAM approach. The 10 performance evaluation metrics showed that the model performed satisfactorily during calibration and validation in terms of the overall fit of observed and simulated stream flows, low flows and the runoff volumes. The Nash-Sutcliffe efficiency (NSE) was >0.85, the Kling-Gupta Efficiency (KGE) was >80% and Volume Efficiency was >59% during calibration. Slight performance drops were noted during validation except for the NSE in Nyatsime catchment whilst the KGE remained relatively high. The validation NSE was >0.65, the Kling-Gupta Efficiency (KGE) was >71% and Volume Efficiency was >55%. Calibrated parameters values showed good time-stability and were well identifiable with posterior parameter distributions having Gaussian shapes. Parameter uncertainty, in relation to total uncertainty was low. Parameter uncertainty constituted about 7% of the total uncertainty region. It was concluded that, although the model only had two parameters, the model performed quite satisfactorily in the simulation of monthly flows which makes it a good tool for operational hydrology and water resources modelling, planning and management especially in regions with inadequate data. © 2013 Elsevier Ltd. Source


Rwasoka D.T.,Upper Manyame Subcatchment Council | Gumindoga W.,University of Zimbabwe | Gwenzi J.,University of Zimbabwe
Physics and Chemistry of the Earth | Year: 2011

Evapotranspiration plays a central role in the water balance of arid and semi-arid areas, as it is the major loss flux. The spatial estimation of actual evapotranspiration is thus of critical importance for hydrologic, environmental and agricultural purposes. This study therefore applied the Surface Energy Balance System for turbulent heat fluxes (SEBS) algorithm to determine actual evapotranspiration in the Upper Manyame catchment in Zimbabwe. The SEBS algorithm was run using atmospherically corrected MODIS satellite imagery on nine clear skies days stretching from 2003 to 2005. SEBS determined actual evapotranspiration was evaluated based on two criteria over Harare-Kutsaga and Grasslands research stations. Firstly, a plausibility or physical consistency check was applied by which SEBS actual evapotranspiration estimates were compared to FAO Penman-Monteith potential evapotranspiration estimates. On average, it was observed that SEBS actual evapotranspiration estimates were physically consistent. SEBS estimates were 36.5% and 76.5% of potential evapotranspiration over Harare-Kutsaga and Grasslands stations, respectively. However, on a few days over Grasslands station SEBS actual evapotranspiration estimates were physically inconsistent as they were greater than potential evapotranspiration. SEBS actual evapotranspiration estimates were also evaluated against actual evapotranspiration from the advection aridity equation. Over Harare-Kutsaga the mean error showed a slight underestimation of 0.32mmd-1 by SEBS and the mean absolute error was 0.5mmd-1. However, over Grasslands station the results were not as good as the mean error and mean absolute error showed an overestimation 2.6mmd-1. This was relatively high. The discussed reasons for the relatively high overestimation errors over Grasslands station include; roughness parameterisation, the spatial variability of input temperature data and heterogeneity. An analysis of the evaporative behaviour of the different land cover types in the catchment showed that: water bodies, closed broadleaved deciduous forests, and open broadleaved deciduous forests had relatively higher mean actual evapotranspiration rates and yet these land cover types constituted less than 5% of the catchment area. Open grasslands were observed to have low evaporative behaviour. Overall this study showed that SEBS has potential for estimating spatial actual evapotranspiration and providing useful information that can be used for water resources and environmental management and planning. © 2011 Elsevier Ltd. Source


Gumindoga W.,University of Zimbabwe | Gumindoga W.,University of Twente | Rientjes T.,University of Twente | Shekede M.D.,University of Zimbabwe | And 3 more authors.
Remote Sensing | Year: 2014

By increased rural-urban migration in many African countries, the assessment of changes in catchment hydrologic responses due to urbanization is critical for water resource planning and management. This paper assesses hydrological impacts of urbanization on two medium-sized Zimbabwean catchments (Mukuvisi and Marimba) for which changes in land cover by urbanization were determined through Landsat Thematic Mapper (TM) images for the years 1986, 1994 and 2008. Impact assessments were done through hydrological modeling by a topographically driven rainfall-runoff model (TOPMODEL). A satellite remote sensing based ASTER 30 metre Digital Elevation Model (DEM) was used to compute the Topographic Index distribution, which is a key input to the model. Results of land cover classification indicated that urban areas increased by more than 600 % in the Mukuvisi catchment and by more than 200 % in the Marimba catchment between 1986 and 2008. Woodlands decreased by more than 40% with a greater decrease in Marimba than Mukuvisi catchment. Simulations using TOPMODEL in Marimba and Mukuvisi catchments indicated streamflow increases of 84.8 % and 73.6 %, respectively, from 1980 to 2010. These increases coincided with decreases in woodlands and increases in urban areas for the same period. The use of satellite remote sensing data to observe urbanization trends in semi-arid catchments and to represent catchment land surface characteristics proved to be effective for rainfall-runoff modeling. Findings of this study are of relevance for many African cities, which are experiencing rapid urbanization but often lack planning and design. © 2014 by the authors. Source


Gumindoga W.,University of Zimbabwe | Rwasoka D.T.,Upper Manyame Subcatchment Council | Murwira A.,University of Zimbabwe
Physics and Chemistry of the Earth | Year: 2011

This paper demonstrates the application of TOPMODEL, a rainfall-runoff model to simulate streamflow of Upper Save River catchment of Zimbabwe based on 2003-2007 hydrometeorological data. The key driver in TOPMODEL, the topographic index was determined using the satellite derived ASTER 30m DEM. The calibration process (2003-2005 period) gave a Nash-Sutcliffe model efficiency (NS) of 0.77 and a Relative Volume Error (RVE) of 6.2%. Sensitivity analysis of the model showed that the parameters most critical for accurately simulating streamflow were: the soil hydraulic conductivity decay parameter (m), the soil transmissivity at saturation (T0) and the root zone available water capacity (SRmax). The model was validated using 2006-2007 hydrometeorological dataset and a satisfactory model performance was obtained (NS=0.73, RVE=-8.6%). We deduce that the ASTER DEM can be used to estimate model parameters for simulating streamflow using TOPMODEL in this catchment. © 2011 Elsevier Ltd. Source

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