Comparison of Rice Growing-stage Evapotranspiration by Water Balance and Eddy Correlation Methods

This paper reports the results of our comparison of evapotranspiration using a paddy lysimeter (30 x 70 m2 plot) by means of the water balance method and the eddy correlation heat balance method to permit a fundamental examination of the overall hydrologic processes. The following results were obtained: (1) In the paddy lysimeter, surface-water levels conformed to underground water levels until ponding water was released, so that changes in the surface-water level could be used to represent changes in the lysimeter’s water storage. On this basis, the water balance method indicated that daily evapotranspiration in July 2003 was about 60% of the level calculated for July 2002, largely because the summer of 2003 was cooler. (2) With hourly calculations in the eddy correlation heat balance method, the estimated daily evapotranspiration in June 2003 was larger than that estimated using the water balance method. Based on 10-day estimation periods, the trends in the two methods were similar (i.e., lower in 2003), but the peaks in both June and August occurred in different 10-day periods. (3) Comparison of daily evapotranspiration levels between the two methods requires improvement in the heat-balance observations.