Evaluation of reference evapotranspiration methods and sensitivity analysis of climatic parameters for sub-humid sub-tropical locations in western Himalayas (India)

The estimation of crop evapotranspiration (ETc) 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. © 2018 Indian Society for Hydraulics.