Abstract
To estimate reliable actual evapotranspiration from a paddy field with flooding water using a simple measurement system, first, the relationship between actual and potential evapotranspiration (LFw,ef and LFPM) was examined. LFw,ef was estimated with the energy balance flux ratio method, and LFPM was calculated by the FAO Penman-Monteith equation. LFw,ef was sufficiently proportional to LFPM in each month of June, July, Aug. and Sept.. Next, actual evapotranspiration (LFw,eb or LFw,ef) was estimated by the energy balance Bowen ratio method or the energy balance flux ratio method, after unreliable values obtained by those methods were corrected from the relationship between reliable values by those methods and LFPM. Potential evapotranspiration (LFpe) was calculated by the equation simplified from the FAO Penman-Monteith equation. The sum of LFw,eb or LFw,ef for a day was sufficiently proportional to that of LFpe, although the value of proportional coefficient in the early growth stage was different from that in the late growth stage. The former value was 0.885, the latter was 0.996. In conclusion, reliable daily actual evapotranspiration could be estimated from daily potential evapotranspiration calculated by the FAO Penman-Monteith simple equation.
