Applicability of standard FAO56-PM ET model with limited meteorological dataset under humid climate of India

Availability of meteorological data of doubtful integrity and/or non-availability of expensive equipment to record them especially in developing countries restricts use of standard FAO56-PM ET model. The present study was aimed to evaluate effective- 0 ness of alternative measures and identify minimum meteorological parameters to obtain at par FAO56-PM estimates for humid Dehradun district of Uttarakhand (India). Daily meteorological dataset for a period of 31 years (1989-2019) was used to evaluate performance of missing meteorological parameters and their different combinations (44 cases) in comparison to full dataset FAO56-PM estimates with statistical indices and their ranks based on global performance indicator (GPI) values calculated using MicrosoftTM Excel as computing tool. The results confirmed that missing actual vapour pressure and saturation vapour pressure (relative humidity) values can be estimated with adequate accurateness by taking dew point temperature equal to minimum air temperature and mean air temperature, respectively, while solar radiation values with great accuracy can be obtained with minimum and maximum air temperature data only. The analysis also confirmed essential requirement of long-term wind speed data as well. Minimum and maximum air temperature along with long-term wind speed data are minimum requirement for calculating FAO56-PM ET estimates in humid areas.