Remote Sensing-Based Estimation Of Evapotranspiration For Irrigation Performance Assessment:

Abstract

Evapotranspiration is one of the climate elements, which plays an important role in water balance and effects on the ecosystem of any region. Evapotranspiration was estimated from meteorological data using food and agricultural organization (FAO) method and using surface energy balance algorithm for land (SEBAL) algorithm from remote sensing data (LANDSAT8 images). The study was conducted at Koga Irrigation project which is located near to Bahir Dar in Mecha Werda. The main objective of this study is to estimate evapotranspiration (ET) for irrigation performance assessment using SEBAL algorithm, cropwat 8 model and the reliable performance indicators. The analysis is carried out using Landsat-8 (OLI/TIRS) data and reference weather parameters like temperature, rainfall, humidity, wind speed and sunshine. The models were prepared to calculate the values of surface radiance, surface reflectance, surface albedo, normalized vegetation index, leaf area index, surface emissivity, surface temperature, net radiation, soil heat flux, sensible heat flux, latent heat flux, which were consequently employed to calculate the daily evapotranspiration at the time of satellite over pass. Interestingly, the result of actual evapotranspiration estimated from SEBAL model in January, February, March, April and May was 0.778, 0.885, 1.01, o.997 and 1.01 respectively. The reference evapotranspiration estimated from FAO method at the time of satellite overpass in January, February, March, April and May was 2.98, 3.39, 3.87, 3.82 and 3.82 respectively. The total amount of crop water requirement and irrigation requirement of Maize were 611.8 and 597.9 respectively. The total amount of crop water requirement and irrigation requirement of Potato and Onion were equal which was 428.6 and 418.6 respectively. This clearly shows that different crops requires different amount of water and also total harvesting time also vary. The study also assessed the performance of Koga Irrigation project based on different irrigation performance indicators were estimated. The indicators were relative water supply, overall consumed ratio, depleted fraction, crop water deficit and relative evapotranspiration which have overall average estimated value of 1.85, 0.55, 0.07, 3.18 and 0.09 respectively. All indicators estimated above were out of the range by standards except crop water deficit that indicates the Koga Irrigation project is not well performed upon its final potential.