Sensitivity Analysis of FAO-56 Penman-Monteith Method for Different Agro-ecological Regions of India

This paper analyzes the sensitivity of reference evapotranspiration (ET o ) to climatic variables for different agro-ecological regions of India: semi-arid (Kovilpatti and Parbhani), humid (Mohanpur), and sub-humid (Ludhiana and Ranichauri). The FAO-56 Penman-Monteith (FAO-56 PM) method is used to estimate ET o , and sensitivity of ET o has been studied in terms of change in maximum air temperature ( T max ), minimum air temperature ( T min ), solar radiation ( R s ), average relative humidity ( RH avg ), and wind speed ( W s ). Sensitivity analysis is performed by increasing and decreasing the climate variables such as T max , T min , R s , and RH avg by one unit of increment and decrement, respectively, up to five units (except for W s ) while keeping the other variables and parameters constant. However, wind speed W s (km h −1 ) is only increased with an increment of one km h −1 up to five km h −1 . The results showed that the change in ET o is linearly related to change in all climate variables ( r 2 = 0.97 in most cases) at all sites. Further, ET o is most sensitive to R s at Kovilpatti, Mohanpur and Ranichauri, and to W s at Ludhiana and Parbhani. However, the sensitivity of ET o to the same variable shows considerable variation from site to site and at the same site within the year. ET o is less sensitive to RH avg followed by T min at all sites.