The Potential Link Between El Nino and Water Hyacinth Blooms in Winam Gulf of Lake Victoria, East Africa: Evidence from Satellite Imagery

Abstract

This study evaluates the link between the occurrence of El Nino events in East Africa and water hyacinth blooms in Winam Gulf of Lake Victoria using remote sensing technology. A time-series of the Normalized Difference Vegetation Index (NDVI) analyzed from data acquired by the multispectral Aqua/Terra sensors aboard the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite are used to monitor areal extent and density of the aquatic plants. We related the NDVI derived from MODIS imagery to data on El Nino South Oscillation (ENSO) events that were obtained from NOAA and rainfall data from the study site. Our results from the 11-year time-series data show a statistically significant positive correlation (R = 0.6, P = 0.021) between the occurrence of El Nino events and water hyacinth blooms in Winam Gulf. The proliferation of water hyacinth rafts in Winam Gulf may be a response to dramatic environmental and water quality changes in Lake Victoria. The patterns of impact of ENSO events and rainfall show spatial and temporal variation patterns in the region, depending on the time and space evolution of each individual ENSO event that could explain the differences in general patterns of water hyacinth cover in Lake Victoria during different El Nino events. Although the problems eutrophication and water hyacinth are severe in the Winam Gulf of Lake Victoria some of the solutions to the problem are located several hundreds of kilometers away in the rich agricultural farmlands of the Lake Victoria catchment area. These include better land management practices and strategies aimed at limiting pollution and soil erosion within the lake’s drainage basin.