Sensitivity of annual and seasonal reference crop evapotranspiration to principal climatic variables

Reference evapotranspiration (ET0) represents the evaporative demand of the atmosphere and depends on climatic parameters such as radiation, air temperature, humidity, and wind speed. Relative role of climatic parameter of ET0 varies from one climate to another and within the climate, and depends on the location and time. Sensitivity analysis was conducted and sensitivity coefficients were determined to evaluate the impact of principal climatic parameters on ET0 in Karnal district of India. Mean monthly ET0 and yearly ET0 from 1981 to 2011 were estimated from FAO-56 Penman–Monteith equation using the daily climate data collected from Central Soil Salinity Research Institute, Karnal. Results showed that seasonal and annual ET0 were most sensitive to maximum temperature followed by sunshine hours. However, wind speed, relative humidity, and minimum temperature had varying effect on mean ET0. After maximum temperature and sunshine hours, ET0 was more sensitive to wind speed followed by relative humidity and minimum temperature in summer. In monsoon, after maximum temperature and sunshine hours, ET0 was more sensitive to minimum temperature followed by relative humidity and wind speed. However, in winter, after maximum temperature and sunshine hours, ET0 was more sensitive to relative humidity followed by wind speed and minimum temperature. The study suggests that the climate variability would affect reference ET0; however, its impact on ET0 would be different for different parameters.