Rainfall in dryland areas is characterized by an erratic and non-uniform distribution that results in frequent dry spells during the monsoon. A direct relationship exists between consumptive evapotranspiration (ET) water use and crop growth/yield. Rockstrom, Hatibu and Oweis (2007) explained that if all the green water captured in the root zone is utilized fully by the crop, yields of 3 tonnes per hectare are achievable in rain-fed agriculture.