Estimation of Evapotranspiration for Irrigation Performance Assessment Using Satellite Remote Sensing at Kobo Valley Irrigation Project, Northern Ethiopia
No Thumbnail Available
Date
2009-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa Universty
Abstract
This paper describes the use of a remote sensing technique, the Surface Energy Balance
Algorithm for Land (SEBAL), to assess actual evapotranspiration across Kobo valley irrigation
project. The SEBAL model was applied to the Landsat 7 ETM+ image corresponding to
December 05, 2003 to produce estimates of ET at 30×30m resolution. The actual
evapotranspiration (ETa) was integrated for 24 hours on a pixel-by-pixel basis from the
instantaneous evapotranspiration (ET). SEBAL ETa estimates vary from 0 to 4.86 mm/day over
the image. Lowest ETa was observed for barren fields and highest for water bodies. ETa for
vegetative areas ranges 3.5 to 4 mm/day. Irrigated areas, drip and sprinkler irrigation systems,
appear to evaporate with average rate of 1.8 mm/day. Penman-Monteith reference crop
evapotranspiration ET0 on the same day was found to be 4.5 mm/day at the meteorological
station. During the dry season, actual evapotranspiration increases with the availability of
moisture in the soil instead of the temperature gradient. The performance of the irrigation
system for the command area (September to January) was determined according to 5 indicators,
namely overall consumed ratio (OCR), relative water supply (RWS), depleted fraction (DF),
crop water deficit (CWD), and relative evapotranspiration (RET). Potential and actual
evapotranspiration parameters used in determining these indicators were estimated according to
the SEBAL (Surface Energy Balance) method using Landsat ETM+ image. Seasonal averages of
the irrigation project calculated from the results were 0.55, for OCR; 1.23 for RWS; 0.29 for
DF; 42.44mm/month for CWD; 0.43 for RET. According to the seasonal average values of all
the performance indicators, the irrigation performance of the area is usually poor and only the
overall consumed ratio indicator is within the range of acceptability. Thus, performance
indicators showed that less irrigation water was supplied to the area than was needed.
Keywords: Performance indicators, performance assessment, evapotranspiration, SEBAL,
remote sensing
Description
Keywords
Performance indicators, Performance assessment, Evapotranspiration, SEBAL, Remote sensing