Abstract
Development pressure has led to serious deforestation on the Indochina Peninsula. Particularly rapid defor-estation has occurred in easily accessible lowland areas, and it is thus important to accumulate knowledge about these forests immediately. We measured evapotranspiration rates for a lowland dry evergreen forest in Kampong Thom Province, central Cambodia, using the energy balance Bowen ratio (EBBR) method based on meteorological data collected from a 60-m-high observation tower. Daily evapotranspiration was higher during the dry season than during the rainy season of the Asian monsoon climate. The seasonal variation in evapotranspiration generally corresponded to the seasonal difference in the vapor pressure deficit. A multi-layer model was used to simulate the seasonal variation in evapotranspiration. The multilayer model also reproduced the larger evapotranspiration rate in the dry season than in the rainy season. However, observed values substantially exceeded model-calculated results during certain periods at the beginning of the dry season and in the late dry season. Moreover, during the rainy season, the model tended to overestimate evapotranspiration. The differences between these observed and simulated values may have been caused by seasonal characteristics of photosynthesis and transpiration in the lowland dry evergreen forest that were not considered in the model simulation.
Highlights
The Indochina Peninsula, including Cambodia, belongs to the Asian monsoon climate zone characterized by distinct rainy and dry seasons
The seasonal variations in solar elevation at noon calculated from the latitude and longitude of the tower site (SE), and observed S↓ and S↑, are shown in Figure 2 (a)
The solar elevation was maximal in April and August, corresponding to the late dry season and the middle of the rainy season, respectively
Summary
The Indochina Peninsula, including Cambodia, belongs to the Asian monsoon climate zone characterized by distinct rainy and dry seasons. Using the energy balance Bowen ratio (EBBR) method, Attarod et al [6] reported higher evapotranspiration rates during the rainy season (4.1 mm day-1) than in the defoliated dry season (2.5 mm day-1) for an artificial teak forest at Mae Moh in northern Thailand. Tanaka et al [7], measuring evapotranspiration by the eddy correlation method for a hill evergreen forest in the Kog-Ma watershed of northern Thailand, reported that transpiration peaks appeared during the late dry season. Lowland dry evergreen forest was once widely distributed over the Indochina Peninsula This forest type is found only in limited areas, such as Kampong Thom Province in central Cambodia. The characteristics of evapotranspiration are described based on comparison with model simulations for the study forest; the simulations were conducted by a multilayer model that was previously applied to a hill evergreen forest of the Kog-Ma experimental watershed in Thailand [7]
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