Lake Tana Volume Monitoring by Integrating In-Situ and Satellite Data
No Thumbnail Available
Date
2018-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AAU
Abstract
Lakes are integrator of environmental changes occurring at a regional to global scale and
present a high variety of behaviors on a variety of time scale. In addition, their crucial
importance as water stocks and retaining given the significant environmental changes
occurring worldwide at many anthropocentric levels has increased the necessity of
monitoring all its morphodynamic characteristics i.e. water level, surface area and volume. In
this thesis, we used satellite altimetry data from Jason and TOPEX to analyze fluctuation in
water level of Lake Tana. Our analysis also combined optical satellite imagery and satellite
altimetry to determine the volume fluctuation of the lake. The use of GRACE gravity data
makes it possible to determine local water storage changes and to assess the water budget
on monthly to multi-annual time scales. The Mann-Kendall trend tests, Sen Slope estimate
and simple linear regression were utilized to detect trends in annual and seasonal extremes.
Altimetry data showed insignificant positive trend detected during the entire study period
(1960 to 2017). The water level of the lake has been increasing at a rate of 0.00574m/year.
The lake exhibited insignificant increasing trend during summer and significant positive
trend during winter, spring and autumn. Water level variations as the eco-hydrological
indicator of the lake are compared for the two periods of natural and anthropogenically
intervened .i.e. 1960 to 1996 and 1997 to 2017. The result of Mann-Kendall trend test shows
that there is a unique insignificant increasing trend of about 0.00243m/year in average
during the recent period of 1960 to 1996 and decreasing trend of about 0. 00225m/year
during the period 1997 to 2017. Moreover, combined analysis of altimetry and remotely
sensed satellite imageries indicated insignificant increasing trend in the volume of the Lake
Tana for the period spanning from 1984 to 2017. However, the volume of the lake has been
decreasing at an alarming rate of 0.612 km
/year starting from the year 2012 to the present.
From alarmingly low value for the remaining water volume in the lake, the lake will
completely disappear within twelve thousands of years if no countermeasures are taken. Geoobservatory
products
such
as
the
GRACE
can
provide
an
accurate
estimate
of
changes
in
total
terrestrial
water
storage
at
a
coarser,
regional
resolution.
The
change
in
storage
fluctuation
of
the
15-year
monthly
data,
from
2002
to
2016
of
the
Lake
Tana
sub
Basin
reveals
total
water
storage
of
the
basin
has
declined by 0.0375mm of equivalent water thickness. a correlation
coefficient of 0.73 and 0.75 is observed between the GRACE estimates TWSC and lake volume
change and TWSC and rainfall respectively.
Description
Keywords
Satellite altimetry, Mann Kendell test, Sen Slope estimate, Tana basin