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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Date
2020-10
Authors
Journal Title
Journal ISSN
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Publisher
Addis Ababa University
Abstract
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.
Description
Keywords
Lake Tana, Water Hyacinth, Evapotranspiration, Water Loss, Climate Variability, Annual, Monthly, Seasonal Time Periods