Transpiration peak over a hill evergreen forest in northern Thailand in the late dry season: Assessing the seasonal changes in evapotranspiration using a multilayer model

Abstract

[1] The seasonal changes in evapotranspiration over a hill evergreen forest in northern Thailand (18°48 0 N, 98°54 0 E), in the Asian monsoon region, were simulated using a multilayer model and the boundary conditions above the canopy. The simulation considered the uncertainty in the leaf area index (LAI) and physiological parameters for both photosynthesis and stomatal conductance models. The parameters were based on the estimated LAI and determined by referring to the measured net photosynthesis rate and stomatal conductance for a single leaf. The simulated cumulative evapotranspiration and rainfall interception agreed with the values obtained from the water budget within these uncertainties. The sensitivity of these limits to both evaporation and transpiration was also investigated. The simulated transpiration peaked in the late dry season. The latent heat flux obtained with the eddy correlation technique showed that the forest continued to transpire in the late dry season. The heat pulse velocities also showed a peak in water use by individual trees in the late dry season. These results counter the view that evapotranspiration declines in the dry season, as has been reported previously for an evergreen forest and other vegetation in Thailand. The transpiration peak was thought to depend on the reduced wetness of the canopy, and the consequent lack of evaporation from it, and on the fact that there was little decline in stomatal conductance, even in the driest conditions.

Role of Land-Atmosphere Interaction on Asian Monsoon Climate

“…The evapotranspiration estimated by a multi-layer model forced by the observed radiation, leaf area index (LAI) and other realistic parameters revealed that a seasonally maximum evapo-transpiration appeared in the late dry season just before the monsoon onset (Fig. 7) when the ground surface was driest in the year (Tanaka et al 2003). A LSM study including the effect of root depth to pump up water in deep soil layer could well simulate this seasonal feature when the mean root depth was set at 6 m (Tanaka et al 2004;Tanaka and Hashimoto 2006).…”

“…Vertical bars indicate ranges of 32 simulated values with the maximum and the minimum, respectively. (Tanaka et al 2003) tion of the atmospheric boundary layer (ABL), and relevant cloud processes at or above the ABL. Betts et al (1998) reviewed the overall possible interactive processes between land surface conditions and the ABL, and emphasized the importance of vegetation and related land cover/use differences on the ABL structure and cloud/precipitation process.…”

Hydrologic sensitivity of flood runoff and inundation: 2011 Thailand floods in the Chao Phraya River basin

“…Regarding the seasonal variations in ET, Tanaka et al (2008) reported that tropical evergreen forest in the mountainous area of the Chao Phraya river basin has a deep soil layer (∼ 5.3 m), which allows fairly steady evaporation throughout a year regardless of the amount of rainfall in different seasons and years (e.g. Tanaka et al, 2003), whereas for diverse land use in northern Thailand, Kim et al (2014) reported that ET becomes higher in the monsoon season than in the dry season with about 10 % interannual variations. Essentially the model behaves in a similar way; i.e.…”

A Dramatic Daytime Decrease in Water Vapor over Coastal Thailand

“…A contrast in soil moisture is clear before and after the monsoon in Thailand (Tanaka et al 2003). Figure 6b shows the simulated results in the same calm situation shown in Fig.…”

“…Air column should be almost saturated owing to a continuous supply of water vapor in large quantities. Therefore, clear diurnal variation in PWV tends to appear in the period before the monsoon, when the soil moisture is lowest around Thailand (Tanaka et al 2003).…”