Assessment of Spatio-Temporal Pattern of Water Hyacinth And Its Dynamic with Seasonal Climate Variability and Impact on Evapotranspiration of Lake Tana Using Landsat And Sentinel-2

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Addis Ababa University


Lake Tana is the largest Lake in Ethiopia which has been invaded by water hyacinth since 2011. However, there is lack of reliable estimates of annual and seasonal water hyacinth distribution and extent. Therefore, this study aims to assess the spatio-temporal pattern of water hyacinth and it’s dynamics with seasonal climate variability and impact on evapotranspiration using Landsat 7 ETM+, Landsat 8 OLI, Sentinel 2 and meteorological data. The area of water hyacinth and surface area of the Lake were mapped using supervised, unsupervised and manual digitizing image classification techniques. The trend of water hyacinth was determined using Mann-Kendall trend test and the impact of climate variability on water hyacinth spatial distribution was studied using Pearson correlation coefficient. The evapotranspiration and water losses were estimated from reference evapotranspiration computed using FAO-56 PenmanMonteith method and a crop coefficient value of 0.65 and 1.90. The results of the study revealed that there was a statistically significant increasing trend in annual spatial coverage of water hyacinth. The annual coverage areas of water hyacinth increased by 96% from 134ha in 2011 to 3019ha in 2019. However, the surface area of the Lake showed a decreasing trend. A total of 1834ha of the surface area of the Lake (0.6 % of the average surface area of the Lake) has lost over the last nine years. The annual maximum lake surface area was 306,399ha occurred in 2015 and the minimum was 302,952ha in 2019. The monthly and seasonal spatial-temporal dynamics of water hyacinth in Lake Tana exhibit a periodic cyclical pattern, reaching the highest peak in Bega followed by a decline to the least coverage level in Kiremt season. The highest growth areal extends of water hyacinth was 3830ha in 2018 November while, the minimum area was 396ha in 2017 July. The monthly surface area of the Lake was varied from 298,392ha in 2016 June to 317,257ha in 2018 July. The seasonal average surface area of the Lake was ranged between 301,817ha in Belg and 307,471ha in Kiremt season. The average daily evapotranspiration of water hyacinth in Lake Tana from 2016 September to 2018 December was 2.39 and 6.99 mm/day, and the average water loss in the Lake due the weed evapotranspiration was 35, 678 and 104,290 m3/day using Kc of 0.65 and 1.90 respectively. The total amount volume of water loss in Lake Tana from 2016 Sep to 2018 Dec was between 30,397,918 m and 88,855,452 m, 3 3 the average value represents 0.21 % of the volume of the Lake using a Kc value of 0.65 and 1.90. The Pearson correlation of monthly water hyacinth and rainfall was significant moderately negative (r= -0.63, p=0.03). The correlation of mean monthly temperature and wind speed with water hyacinth was negative (r = -0.34, p = 0.28) and (r = -0.59, p = 0.04) respectively. The seasonal correlation of the area of water hyacinth with rainfall and wind speed was insignificant moderately negative (r= -0.72, p=0.49) and (r= -0.62, p=0.57). Low insignificant negative correlation (r = -0.36, p = 0.76) with mean temperature was also attained in seasonal period. In general, the climate variability in Lake Tana Basin showed a less and insignificant contribution for distribution and spread of water hyacinth in study period.



Lake Tana, Water Hyacinth, Evapotranspiration, Water Loss, Climate Variability, Annual, Monthly, Seasonal Time Periods