Remote Sensing and Gis Based Determination of Evapotranspiration of Lake Tana Basin, North Ethiopia
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Date
2015-06
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Addis Ababa Universty
Abstract
Lake Tana Basin which is found in Northwest highlands of Ethiopia has high potential for
irrigation agriculture, hydroelectric power development and ecotourism. This basin has been
identified as one of the economic growth corridors of the country and several hydropower
and irrigation projects are being implemented. Hence, there is an increasing demand of water
utilization and the water resource systems show variations in their accumulated flow,
distribution and overall storage volume with time. The basic objective of this research was to
estimate the daily and seasonal evapotranspiration of Tana basin and mapping its spatial
distribution in different land use and land cover types. The Surface Energy Balance
Algorithm for Land (SEBAL Model) was applied to three Landsat TM satellite images
corresponding to November 18 and 27, 2011 to produce estimates of instantaneous actual
evapotranspiration at 30×30m resolution for the satellite over pass time. Then, the
instantaneous actual evapotranspiration was extrapolated to the daily ET value and seasonal
accumulated ET values using the evaporative fraction which derived from the satellite images
and the Penman Monteith reference evapotranspiration that was computed from
meteorological data of the basin. The daily Penman-Monteith reference evapotranspiration
ET0 which calculated from meteorological data of the basin was found as 4.3 mm/day. The
actual evapotranspiration of the basin computed using SEBAL model ranges from 0 to 4.3
mm/day that observed on bare lands and water bodies of the basin, respectively. The large
portion of the basin has the range of evapotranspiration between 1.3 to 2.3 mm/day which
covered by agricultural crops and grasslands. The dry season evapotranspiration of the basin
also measured between 20 to 439 mm depth of water. The spatial distribution of
evapotranspiration is related to the distribution of vegetation in the basin. The eastern and
western parts of the basin show lower evapotranspiration corresponding to their little or no
vegetation cover while the downstream of the Lake has relatively higher evapotranspiration
due to its relatively dense vegetation cover. Finally, the daily SEBAL ET was compared to
the Penman Monteith daily reference ET and the linear regression analysis shows that daily
ET of the SEBAL model has a strong relationship with Penman-Monteith reference
evapotranspiration of the study area.
Key Words: Evapotranspiration, Remote Sensing, Surface Energy Balance, SEBAL Model
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Keywords
Evapotranspiration, Remote Sensing, Surface Energy Balance, SEBAL Model