Estimating the radiation component for using Morton models to estimate evapotranspiration.
This function returns a object named variables which contains variable values for implementing Morton CRAE and CRWE formulations
McMahon, T., Peel, M., Lowe, L., Srikanthan, R. & McVicar, T. 2012. Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis. Hydrology and Earth System Sciences Discussions, 9, 11829-11910.
Morton, F.I. 1983, Operational estimates of areal evapotranspiration and their significance to the science and practice of hydrology. Journal of Hydrology, vol. 66, no. 1-4, pp. 1-76.
Morton, F.I. 1983, Operational estimates of lake evaporation. Journal of Hydrology, vol. 66, no. 1-4, pp. 77-100.