Estimation of Evapotranspiration and Crop Water Productivity by using Remote Sensing:  A case study of Shikarpur District, Pakistan

The growing population requires an increase in food production; however, water scarcity is increasing globally. Pakistan's agriculture primarily depends on the Indus River, which is facing an extreme water shortage. Challenges to the country's water and food security are increasing due to inefficient irrigation practices and poor policies. In such conditions, the estimation of crop water productivity is necessary for managing water resources and food production.  Crop water productivity is defined as the relationship between the water used per kg of crop yield or crop yield per accumulated actual evapotranspiration. Evapotranspiration, which plays an essential role in calculating crop water productivity, is the combination of water loss due to evaporation from the surface of the earth and transpiration from the plants. The wheat crop, a Rabi-season cash crop of Sindh province, is considered in this study. Shikarpur, a district of upper Sindh in the Begari Canal Command Area (CCA), is selected for the study. An accurate estimate of evapotranspiration (ET) and crop water productivity (CWP) at a regional scale is essential to enhancing the practice of water-saving agriculture in Pakistan. In this research, ET and CWP of the wheat crop in Shikarpur from November 2019 to April 2020 were estimated by using a satellite-derived ET product downloaded from EEFlux, which processes satellite data using the METRIC method with tall alfalfa referenced by using the Penman-Monteith method. The actual ET is calculated from the reference ET fraction (ETrF) of satellite data and the reference ET (ETr). According to the Bureau of Statistics, Planning, and Development department of Sindh, the area of wheat crop and yield for the years 2019–20 in Shikarpur are 36,007 hectares and 100,623 metric tons, respectively. The data for the year 2019–20 is used because the wheat crop mask used for the study is from the same year. The average actual evapotranspiration of the wheat crop in the initial, crop development, mid, and late stages was found to be 29.44 mm, 75.89 mm, 131.17 mm, and 107.11 mm, respectively. The total average evapotranspiration of the entire season of the wheat crop is 343.66 mm, and the CWP of Shikarpur district is found to be 0.81 kg/m3in the years 2019–20.