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Tipping-bucket flow meter and rain gauge (TBFM/TBRG) are widely used for the measurement of gross rainfall ( GR), throughfall ( TF), and stemflow ( SF) to evaluate the amount of interception loss ( I). However, TBFM/TBRG cannot measure the inflow rate during tipping and underestimates the inflow rate. To correct this systematic bias, 33 total calibrations were conducted for five types of TBFM/TBRG in the laboratory. The tipping time increased with the bucket volume, and the underestimation during one tip was higher for TBFM/TBRG of larger capacity. With the use of the scaled actual inflow rate and the actual volume of a single tip from the measured static volume of a single tip when the inflow rate is zero, the common calibration curves were obtained as quadratic equations for each of the five types within an error range of ±3%. We measured GR and TF by using TBRG and TBFM with a resolution of 0.2 mm and measured SF by TBRG with a single-tip static volume of 15.7 cm3 in a Japanese temperate coniferous forest (TCF) and a Cambodian tropical deciduous forest (TDF). At both sites, the calibration curves needed to be applied to obtain GR, TF, and SF on an event scale with an underestimation degree of less than 3%. Without applying any calibrations, the higher rainfall intensities in TDF caused larger underestimations of GR, TF, and SF and larger overestimations of I compared with results for TCF. On an annual scale, the degree of overestimation of I relative to GR (Δ I/ GR) was 1.2% in TCF and 3.5% in TDF, and Δ I/ I was at least 10% at both sites. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Both evergreen and deciduous forests (Efs and Dfs) are widely distributed under similar climatic conditions in tropical monsoon regions. To clarify the hydraulic properties of the soil matrix in different forest types and their effects on soil water storage capacity, the soil pore characteristics (SPC) were investigated in Ef and Df stands in three provinces in Cambodia. Soils in the Ef group were characterized in common by large amounts of coarse pores with moderate pore size distribution and the absence of an extremely low K at shallow depths, compared to Df group soils. The mean available water capacity of the soil matrix (AWC) for all horizons of the Ef and Df group soils was 0·107 and 0·146 m m, respectively. The mean coarse pore volume of the soil matrix (CPV) in the Ef and Df groups was 0·231 and 0·115 m m, respectively. A water flow simulation using a lognormal distribution model for rain events in the early dry season indicated that variation in SPC resulted in a larger increase in available soil water in Ef soils than in Df soils. Further study on deeper soil layers in Ef and each soil type in Df is necessary for the deeper understanding of the environmental conditions and the hydrological modelling of each forest ecosystem. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This article discusses a study which investigated the river water interactions between the Tonle Sap in Cambodia and the Mekong rivers using the stable isotope ratios of oxygen. The researchers found that the contribution rate of the Tonle Sap water to the Mekong river water during the peak flow period of the Tonle Sap River was approximately 70-97 percent along the right bank and 0-5 percent in the middle and the left banks of the Mekong. They found the contribution ratio along the right bank remained as high as 80 percent, even 21 kilometers downstream from the confluence.

This article discusses a study which measured evapotranspiration in an evergreen broadleaf forest watershed in the Kampong Thorn Province of central Cambodia. The main vegetation species at the study site were Myristica iners and Vatica odorata. The researchers used a meteorological observation tower. They found the evapotranspiration similar in the middle of the dry season and the late rainy season. They attributed this stability due to the shallow ground water here resulting in no significant difference in soil moisture.

This article discusses a study which observed the micro-meteorology from a tower in an evergreen forest in Central Cambodia. The researchers found that the stability length indicates the atmospheric condition between weakly unstable and weakly stable 63 percent of the time. They also noted that the calculated Richardson number was smaller than the critical Richardson number (0.2) 72 percent of the time. The researchers concluded that the atmospheric stability which prevailed was generally suitable for tower flux observations.

• ET and its components were measured separately in a tropical dry deciduous forest. • Understory ET is important, contributing 35% to whole-ecosystem ET. • Overstory LAI strongly affects the proportion of understory ET relative to whole ET. • Underestimates of stand transpiration can be corrected with calibrated coefficients. The water balance of tropical dry deciduous forests is less well understood than some other forest ecosystems. To help close this knowledge gap, we separately measured the evapotranspiration from the whole ecosystem (ET W), transpiration (TR) and interception loss (IL) from overstory trees, and evapotranspiration from the understory vegetation (ET U) in a tropical dry deciduous forest in Cambodia. It was found that ET W was equivalent to 73.7% of rainfall (P) at the annual scale. In the dry season, ET W corresponded to 120.1% of P , which indicates the utilization of soil water replenished during the wet season. The sum of transpiration estimated by the thermal dissipation (TD) method with the original coefficient (TR G), IL , and ET U was smaller than ET W, except for the middle of the dry season, due to an underestimation of TR G. Although recently reported calibration coefficients can reasonably correct TR G , future calibrations of the TD method are highly recommended for the precise evaluation of single-tree-scale transpiration in tropical dry forests. The annual contribution of the understory vegetation to ET W (ET U / ET W) was 34.6%, leading to the conclusion that the understory vegetation cannot be ignored when trying to gain a comprehensive understanding of the hydrologic cycle in tropical dry forests. The seasonal variations in ET U / ET W were mainly controlled by the leaf area index (LAI) of overstory trees, resulting from the overall stability of ET W and decreasing trend of ET U with increasing LAI in the wet season, with the opposite holding true in the dry season, i.e., decreasing ET W with the decline of LAI and less variations of ET U. Thus, LAI influenced both the seasonality and the annual contribution in ET U / ET W , exerting a notable influence on hydrological cycling in this forest. [ABSTRACT FROM AUTHOR]