Abstract:
Several studies showed that the Penman method is superior, when the required data are available and reliable to all other commonly used methods for estimating ET0 under varying locations and climatic conditions. More physically based FAO-56 Penman—Monteith (PM) combination method yields consistently more accurate ETD estimates across a wide range of climates. Methodologies on crop water requirements were reviewed at international level to advice on the revision and update of procedures for estimating ET° and the panel of experts recommended the adoption of the FAO-56 Penman - Monteith combination method as standard. Hence for the present study, the same method was chosen as the standard method for the calculation of reference evapotranspiration. Monthly normal climatic parameters like maximum temperature, minimum temperature, minimum relative humidity, maximum relative humidity, wind speed and sunshine duration was colleted for 167 locations in all over India. Reference evapotranspiration was calculated for all locations in the India using FAO-56 Penman Monteith method. Climatic zones were prepared using Arc. GIS 9.1 software. Reference evapotranspiration zones were demarcated through out the India based on daily ETc values. These ET0 zones will be useful to calculate daily crop water requirement in that particular area. Further, it will be useful for accurate estimation of surface runoff. Maximum daily reference evapotranspiration was varying from 4.71 mm to 11.17 mm at Bhaunagar and Indore. respectively. Minimum daily reference evapotranspiration varies from 0.61 mm to 2.47 mm at Srinagar and Darjeeling respectively. Maximum reference evapotranspiration was observed in the month of May and minimum reference evapotranspiration was observed in the month of January.
