Detecting level of wetland encroachment for urban agriculture in Uganda using hyper-temporal remote sensing

Abstract

Background: Urbanization is an important indicator of economic growth and social change but is associated with environmental degradation. In Uganda, wetlands cover an area of 11% of the country’s land area, of which half have been converted to industry and residential areas, and urban agriculture. Here, we investigate the extent of wetlands lost in two Ugandan cities, Wakiso and Kampala, in a period of 30 years. Secondly, we demonstrate a simple methodology to monitor agriculture on encroached wetlands. Methods: Using a field survey and free remote sensing data from Landsat TM 1986 and Landsat ETM 2016 we classified the rate of wetland loss and encroachment from 1986 to 2016. Using MODIS NDVI 16-day composites at 500-meter spatial resolution, we generated distinctive crops and crop mixtures in the encroached wetlands for urban agriculture using the ISODATA clustering algorithm. Results: Over 30 years, 72,828 ha (73%) of the Wakiso-Kampala wetlands have been lost. Agriculture areas have doubled, of which 16,488 ha (23%) were reclaimed from wetlands. All cultivated agriculture in Kampala was in the wetlands while in Wakiso, 73% of crop agriculture was in the wetlands. Major crops grown in these urban wetlands were banana (20%), sugarcane (22%), maize (17%), Eucalyptus trees (12%), sweet potatoes (10%). Conclusions: The Kampala-Wakiso wetlands have been disappearing at a rate of 2500 ha annually for the last 30 years. At this rate, there will be no wetlands left by 2029. Policy recommendations should promote wetland reclamation programs so as to restore and reconstruct lost and fragmented wetlands; should mandate food security and poverty eradication to convene with ministries regulating wetlands to merge conflicting policies; and should develop polices that are inclusive of challenges faced by the urban poor while at the same time minimize the pressures on urban environments.