Heat balance model over a vegetated area and its application to a paddy field

A new canopy model having a simple parameter is here presented for estimating the diurnal or seasonal variations of the heat balance, employing meteorological data of temperature, wind, humidity, precipitation, and solar radiation gathered by AMeDAS near the experimental field. The calculated results were compared with observations over the rice paddy field for the two-year period of 1993 and 1994. Simulations using the presently developed canopy model agreed well with the daily-mean observed values. The rms error in the daily mean values between the observed and calculated values of surface temperature, sensible heat flux, and latent heat flux were 1.7 degrees C, +/-13 Wm(-2), and +/-16 Wm(-2), respectively, during the overall observational period. The annual evapotranspiration was evaluated as about 600 mmy(-1). This value is found between the values for shallow water (564 mmy(-1)) and forests (692 mmy(-1)). The ratio of rainfall interception to evapotranspiration during the vegetated periods are about 18 % and 9 % for the year 1993 (cool summer) and 1994 (hot summer), respectively. The precipitation amount in 1993 is large, while evapotranspiration from the vegetation is small, resulting in a large rate of rainfall interception.