Landuse Dynamics in a Small Watershed of the Semi-arid Zimbabwe

Zimbabwe has experienced a controversial land reform program with physical, political and socio-economical consequences for the country and the entire southern African region. Here, land use decision making is related to water. A study has been undertaken in Insiza River watershed (3401 km 2), located within the semi-arid southern part of Zimbabwe. The Insiza River is a tributary of Mzingwane River, which drains into the transboundary Limpopo River, contributing around 9 % of the unit runoff of the latter river. The Insiza watershed is divided into two main hydrological zones, the Upper Insiza and the Lower Insiza. Mean Annual Runoff of the two hydrological zones is 50 mm and 38 mm respectively. Through a supervised classification of satellite images, the landuse dynamics was assessed from Landsat images acquired in April 1991 and April 2000. Five signature files, bare ground, water bodies, mixed impacted land, good natural vegetation and croplands were used to define the Insiza watershed land use set up while processing Landsat images with IDRISI. For the decade considered, the major changes occurred within mixed impacted lands that were converted into croplands. This conversion was observed on 14% of the total area of the Insiza watershed. Moreover there was a decrease in water bodies (from 1.3% to 0.89%), bare ground (from 1.2% to 0.9%) and in natural good vegetation (from 50.99% to 50.48%) land types. These changes were observed in the Upper Insiza, where the commercial farms were located. However, the decrease in natural good vegetation and the conversion of mixed impacted lands into fields took place mainly in the communal lands.