2004 Volume 17 Issue 5 Pages 482-492
Evapotranspitation (ET) in a tropical rain forest, Bukit Tarek Experimental Watershed in Peninsular Malaysia, was calculated using the short-time period water-budget (SPWB) method. We selected the dates when precipitation was less than 2.0mm d-1 for the starting and ending days of the short-time period because we obtained reasonable results and sufficient sample numbers. ET ranged from 2.0 to 5.4mm d-1(mean of 4.0mm d-1 and S.D. of 0.83) for a 3-yr period (1992-1994). The SPWB method underestimated ET during the transition from wet to dry conditions and overestimated ET during the transition from dry to wet conditions. These errors resulted because surface soil moisture did not remain constant for the periods. In comparison, ET estimated by SPWB method taking soil water storage into account (SPWB-S method) ranged from 2.7 to 4.9mm d-1 (mean of 3.8mm d-1 and S.D. of 0.57) for a 2-yr period (1993-1994). Potential evapotranspiration (EP), estimated by the Penman equation, was lower than ET estimated by SPWB-S method. The evapotranspiration ratio of ET to EP was 1.38. This value is useful for estimating actual ET by the Penman equation in this region.