Hydrological Impacts of Urbanization of Two Catchments in Harare, Zimbabwe

Abstract

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 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.

Effects of changes in land use and climate on water availability of a tropical catchment

“…As impervious area increases, less water infiltrates into the soil resulting in lower soil water storage. Several studies have investigated the correlation between urbanization and the water balance in tropical regions (Wagner et al, 2013;Gumindoga et al, 2014a;Remondi et al, 2016) and results are similar to ours.…”

“…Numerous studies argue that different types of land use have different water use and water storage characteristics, thus different land use distributions may result in different distributions of water in space and time (Bruijnzeel, 1989;Sahin & Hall, 1996;Brown et al, 2005;Romanowicz & Booij, 2011;Gumindoga et al, 2014a;Zhang et al, 2016;Marhaento et al, 2017a). Studies in tropical regions have shown that changes from vegetated areas into settlements may significantly reduce canopy interception and soil infiltration capacity, resulting in a large fraction of precipitation being transformed into surface runoff (Bruijnzeel, 2004;Valentin et al, 2008;Marhaento et al, 2017a).…”

Effect of landcover/land-use changes on water availability in and around Ruti Dam in Nyazvidzi catchment, Zimbabwe

“…Alternative methods have been developed in recent years which provide rapidly available hydrological data over large areas based on remote-sensing techniques. Satellite data can be used to: derive terrain parameters using freely available elevation data (Maathuis and Wang, 2006;Gumindoga et al, 2011), estimate soil moisture (Horváth, 2002;Meier et al, 2011), estimate rainfall (Habib et al, 2012;Haile et al, 2013), quantify evapotranspiration Rientjes et al, 2013) and determine landcover parameters (Dube et al, 2014;Gumindoga et al, 2014a;Gumindoga et al, 2014b).…”

Impacts of landcover changes on streamflows in the Middle Zambezi Catchment within Zimbabwe

“…Parameters were calibrated for a reference period and the simulated runoff compared to observed runoff in periods with potential change (Seibert and McDonnell, 2010). To detect if there has been any changes as a result of land use, all the optimized parameters and the input variables derived from running the model for the period 2000 to 2008 were held constant as in Gumindoga et al (2014), then the land cover parameters were varied to 1989, 1998 and 2014 ones and the model simulated again to observe if there were any differences to the runoff simulated In the model setup, only the catchment characteristics derived from land cover maps were changed, the precipitation, temperature and evapotranspiration values which were applied to simulations for the period 1998 to 2008 remained unchanged thus model forcing re- The "+" sign means an increasing trend and the "−" sign means a decreasing trend. *: statistically significant at 5 % level.…”

“…The recent interests towards integrated management of land and water has renewed the need of quantifying the hydrological impacts of land use changes (Gumindoga et al, 2014) The integrated management of land and water resources will facilitate more productive and sustainable utilisation of the natural resources available in the basin.…”