Abstract:
Agriculture in Pakistan largely depends upon irrigation, and about 90% of the total agricultural production is obtained from irrigated lands. For the better assessment and management of irrigation water requirement, the estimation of consumptive use of water for agriculture is very important. One of the key components of the water cycle is evapotranspiration (ET). Conventional techniques for measurements of ET are point based and representative of the only local scale. Satellite remote sensing data with large area coverage and high temporal frequency provide measurements of several relevant biophysical parameters required for estimation of ET at regional scales. This study uses Surface Energy Balance System (SEBS) Model to calculate daily actual evapotranspiration (ET a) in Lower Chenab Canal (LCC) irrigation system using MODIS data for clouds-free days. As there is no flux tower in the study area for direct measurement of latent heat flux and sensible heat flux, therefore, the model estimated values of ET a were compared with reference evapotranspiration (ET 0). Results showed that values of actual ET are much closer to reference ET in the winter months with the value of mean difference between ET0 and ETa of 0.36 mm/day, while in summer season the mean difference of 1.5 mm/day. Regression analysis was also performed to test significance of irrigation discharge on actual ET. There was found a nonSignificant impact of irrigation discharge on actual ET. This relationship indicates that ET does not depends only upon irrigation discharge but also on multiple factors like ground water table, moisture in root zone, precipitation, and temperature, etc.
