Evapotranspiration Estimation Using Surface Energy Balance-Based Evaporative Fraction for Water Management in Canal Irrigation Command

Abstract

In the present study, the actual evapotranspiration was estimated using the remote sensing-based spatiotemporal approach of evaporative fraction for canal irrigation command (Ozat-II) in Junagadh, Gujarat state, India. The evaporative fraction (EF) in the spatial and temporal data is useful for the estimation of regional and temporal evapotranspiration (ET) for irrigation scheduling in irrigation command. The remote sensing-based surface energy balance algorithm for land (SEBAL) use the images from the satellite to estimates ET using EF. The land surface temperature (LST) and its relation with EF can be used to estimate ET using SEBAL approach. The Landsat-7, 8 images of summer season were used to derive the Normalized Difference Vegetation Index (NDVI) and LST, whose values ranged from 0.31 to 0.90 and 304.76 K to 311.00 K, respectively, in the agricultural land with crop in the command area. The SEBAL-based EF values were ranged from 0.11 to 1.00 over the canal irrigation command area. The temporal data of evaporative fraction indicate that the lower values of EF were observed during initial and end crop growth stages, i.e. March, first fortnight of April and late May which revealed the low vegetation cover. The values of EF increased in the agricultural crop land as the higher value of EF was observed as 0.84 during 116 (April 26, 2014) due to the application of irrigation from canal network and the lower value of EF was observed as 0.62 during 140 (May 20, 2014) during dry period of the season. As the NDVI increases, the evaporative fraction was also increased and the seasonal variation of NDVI was similar to the seasonal variation of EF. The relation between the EF and surface temperature, T S , was developed and gives the negative correlation with R 2 of 0.626 for agricultural land; this can be helpful to estimate spatiotemporal ET value. The remote sensing-based daily actual evapotranspiration (AET) values were ranged from 3.75 to 7.37 mm/day and FAO-56-based daily crop evapotranspiration (ET c ) values were ranged from 4.62 to 8.97 mm/d for groundnut crop. The water use efficiency (WUE, kg/ha.mm) for summer groundnut was estimated as 4.03 kg/ha.mm per the SEBAL-based actual evapotranspiration (AET) and as 4.38 kg/ha.mm as per FAO-56-based crop evapotranspiration (ET c ). The SEBAL-based AET can be used for the irrigation scheduling in the canal irrigation command for efficient water use.