Remote Sensing and Gis Based Determination of Evapotranspiration of Lake Tana Basin, North Ethiopia

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Addis Ababa Universty


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



Evapotranspiration, Remote Sensing, Surface Energy Balance, SEBAL Model