Abstract:

This paper applied the formulas of Penman and the forest ecosystem evapotranspiration which is deduced in terms of theorization to calculate the potential evapotranspiration and the evapotranspiration of the monsoon evergreen broad-leaf forest in Dinghushan, Guangdong Province. The results are given as follows: 1.The annual average potential evapotranspiration of the monsoon evergreen broad-leaf forest in Dinghushan is 987.5 mm and is 47% of the corresponding period rainfall. The highest is in July and the lowest is in February. This is mainly consistent with the variations of temperature, but is detained with the rainfall. 2.The annual average evaporation of free water is 1194.5 mm. The potential evapotranspiration is much smaller than the evaporation of free water in dry season while the both are very close in wet season. So the parallel of both is a referenced index for divieded dry and wet season. 3. The annual average evapotranspiration by theoritic formula is 951.9 mm and is nearly equal to the potential evapotranspiration. It is 45.3% of the corresponding period rainfall. 4. The annual average total runoff the monsoon evergreen broad-leaf forest in Dinghushan is 1103.8*!mm and the coefficient is 0.52. The annual average variation of store water is 38.9 mm. The annual average evapotranspiration by water balance is 960.1 mm and is very close to by theoritic formula. The system error is under 1% in three years. It has a preliminary result that the theoritic formula is worth spreading method for calculating the evapotranspiration of forest ecosystem.

Key words: Subtropical, Broad-leaf forest, Forest ecosystem, Potential evapotranspiration, Evapotranspiration, Water balance