Calculation and validation of actual evapotranspiration from satellite derived indices with observed data in delineated agro-climatic zones of Punjab using remote sensing and GIS techniques

Water is the major restrictive constraint for agricultural growth and production. Agro-climate zones refer to the areas with homogenous agro-potential characteristics. The objective of this study is to delineate the agro-climate zones of Punjab, Pakistan and to calculate Actual evapotranspiration (ETa) from actual and satellite data. Potential evapotranspiration (ET0) was calculated by using climatic normal of 25 years (1990-2015). On the basis of Potential evapotranspiration (ET0) and Moisture Index, study area was delineated into seven agro-climatic zones. Secondly, ETa was investigated by adopting a fraction of Normalized difference vegetation index. Landsat 8 data for the year (2016) was used to determine pixel-based vegetation coefficients. Actual ET maps were prepared to analyze spatial variation of ETa in all zones. Actual ET was determined in mm/day. Daily ETa values in the months of Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct and Dec were 1.0, 1.71, 2.70, 3.5, 4.41, 5.01, 5.2, 4.5, 4.37, 3.01, 2.0 and 1.4 mm respectively. Finally, it was observed that there is a strong relation between both results calculated from satellite data and climatic data of selected crops, i.e.wheat, rice, cotton, sugarcane and maize R²=0.96, 0.94, 0.90, 0.98 and 0.95 respectively. Above results shown that satellite data are widely useful with ground validation for sustainable crop production as well as for policy makers with respect to water conservation.