灌漑・排水システム工学

Comparison of Different Methods to Estimate Mean Daily Evapotranspiration from Weekly Data at Patna, India

Abstract

Upadhyaya A

Estimation of evapotranspiration is necessary for efficient water management and crop planning. Fifteen different methods of ET0 estimation were employed to compute daily reference evapotranspiration for the period 2010 to 2014. In the absence of reliable open pan evaporimeter data, FAO-56 Penman Monteith method was considered as one of the reliable method of ET0 estimation. The results showed that mean weekly evapotranspiration values obtained from Penman-Monteith method were very closer to FAO-56 Penman-Monteith method and values from all the other methods except FAO- 24 Pan, Christiansen Pan and Hargreaves methods generally predicted higher values of mean weekly daily ET0 in comparison to FAO-56 Penman-Monteith method. The analysis shows that mean weekly daily ET0 estimates of combination methods resulted better ET0 estimates than radiation, and temperature and evaporation methods. Weekly ET0 values estimated by FAO-56 Penman-Monteith method were found to vary in the range of 1.3 mm/day to 6.7 mm/day. Average annual reference evapotranspiration was found as 1517.1 mm.