The estimation of crop evapotranspiration (ET_c) uses reference evapotranspiration (ET₀) as a key variable. Physically based FAO-56 Penman–Monteith method provides accurate ET₀ estimates; however, various methods are still used in different climatic regions worldwide, either due to simplicity of the methods or due to insufficiency of data required for Penman–Monteith method. The present study is conducted at sub-humid sub-tropical locations of western Himalayan agro-climate in the Indian state of Himachal Pradesh. Performance of 12 ET₀ methods, representing combination type, pan evaporation, radiation and temperature based, is compared with Penman–Monteith method. Different ET₀ methods are ranked on the basis of quantitative comparison performed on mean daily ET₀ obtained for a period of 6 years. The temperature-based methods performed better than radiation and pan evaporation-based methods. Linear regression equations are developed between Penman–Monteith ET₀ (dependent variable) and ET₀ estimates from alternate method (independent variable). Relative significance of meteorological factors essential for accurate ET₀ estimation in the climate considered is investigated using sensitivity analysis. Solar radiation is identified as the most sensitive parameter for ET₀ estimation in the climate of the study area, followed by maximum temperature and relative humidity.

Water shortage is the prominent limiting factor for agricultural sector in developing countries. The efficient water use is required which helps to obtain effective irrigation schedule for various crops. The present study aims at establishing optimized irrigation schedule for potato, which is a major cash crop in Northern India. Study is conducted in open field plot of Agricultural Experimental Station at National Institute of Technology Hamirpur (India) for Potato during 2013–2016. Irrigation scheduling models based on root water uptake and growing degree days concept are used to workout irrigation schedule for potato in the study. Comparison of field observed and modelled values of percentage moisture depletion in different depths and soil moisture variation at various depths is performed to evaluate the models efficacy in estimating soil moisture extraction by the potato crop for the crop period and replications during study period. Root uptake-based model is found to have better agreement with observed values. The irrigation schedule developed helps in optimal use of irrigation water in water scarce areas.