Water stands as a vital input with a pivotal role in global agricultural production. Its significance transcends ecosystems, particularly in the context of agricultural systems that lay the foundation for wetland and marine ecosystems. Accurate irrigation scheduling and accurate crop water requirement measurement are both necessary for effective water management of crops. For the best plant growth, irrigation is used to replenish the moisture that has been lost. The reference evapotranspiration is crucial in determining the water requirements for crops and the timing of irrigation. For irrigation planning and water management, an accurate calculation of the crop water requirements (ETc) is important. Accurate irrigation scheduling and accurate crop water requirement measurement are both necessary for effective water management of crops. For the best plant growth, irrigation is used to replenish the moisture that has been lost. The reference evapotranspiration is crucial in determining the water requirements for crops and the timing of irrigation. Accurate calculation of any crop's ETc. This paper conducts an assessment and analysis of crop evapotranspiration estimation and the corresponding irrigation water requirement for various crops. It delves into the utilization of diverse evapotranspiration models and data within the context of geographical ecology studies. Additionally, the paper employs these methodologies to estimate daily water needs for agricultural crops cultivated in different climatic zones, both in India and globally.