Survey on Spatial Variability of Surface Soil Moisture and Soil Physical Properties in a Sloping Grassland Field

Spatial variability of surface soil moisture, bulk density, satureted hydraulic conductivity, and penetration resistance (cone index) in a sloping grassland field were surveyed. The typical results were as follows: (1) The surface soil moisture and the bulk density were normally distributed at a significant level of 0.05. (2) The surface soil moistures were higher at low area than in high and slope area. The coefficients of variation were larger at slope area. (3) The coefficients of variation for bulk density were larger at slope area than in low area. (4) The distribution of saturated hydraulic conductivity can be considered to be log-normally distributed. (5) The cone index showed the normal distribution

Amplitude Domain Reflectometry法による不飽和砂地盤中のNAPL含有量と誘電率に関する基礎的研究

Subsurface contamination by non-aqueous phase liquid (NAPL) has become a serious environmental issue. Therefore, it is necessary to estimate the NAPL content (θNAPL) in unsaturated soil to detect and monitor the NAPL contaminations in soil and groundwater. The objective of this study was to investigate the relationship between θNAPL and permittivity (K) in unsaturated sandy soil as a fundamental study to estimate the θNAPL. An ADR (Amplitude Domain Reflectometry) method was used to measure the K in the soil including the NAPL which was a castor oil as light NAPL or a HFE-7100 as dense NAPL. The experimental study indicated the linear relation between θNAPL and K in unsaturated soil with soil-NAPL-air. Using this relationship, we can estimate the θNAPL. On the other hand, although we obtained the relationship between θNAPL, θw and (root) K in unsaturated soil with soil-NAPL-water-air, it was not possible to estimate the θNAPL using this relationship

Improvement of complementary relationship-based evapotranspiration model

Advection-Aridity(AA) model can calculate actual evapotranspiration by using only meteorological data. However, comparing the model with Penman equation showed that AA model doesn’t properly evaluate evapotranspiration from urban moisture area. In urban area, Actual evaporation from water calculated by AA model(E) are much less than that by Penman equation(Epo). Multiple regression analysis using estimation results indicates that the difference between the models is due to the difference of the sensitivity to vapor pressure deficit between the models. To improve this problem, modification coefficient k, defined as k=a･albedo+b, is suggested. Regression coefficients a, b are determined as satisfying k=Epo/E for water and k=1 for urban surface. By using this coefficient k, evaporation from water is nearly equal to value estimated by Penman equation, while evaporation from urban surface is changeless

Long-term Trend of Rainfall at Tsudaka Farm of Okayama University

Characteristics of long-term change in rainfall at Tsudaka Farm of Okayama University were analyzed with data during the 20 years, from 1979 to 1998. The typical results were as follows: (1) The average of annual rainfall was 1203 mm at average, 1726 mm at maximum, and 666 mm at minimum. (2) The decreasing rate of the annual rainfall was 5.37 mm/year. (3) Trend of rainfall intensity in each rainfall duration showed an increase of which rate were 0.005~0.256 mm/h/year, contrary to the annual trend. (4) Rainfall intensities in n-years probability were estimated using the maximum rainfall intensity for each rainfall duration

Measurement of thermal conductivity in the soils of Shirakami Mountains

Thermal conductivity of soils in Shirakami Mountains that was registered on UNESCO's World Natural Heritage in 1993 were measured using a twin transient-state cylindrical-probe method. The typical results were as follows:(1) Thermal conductivity of the soils in Shirakami Mountains increased according to an increase of soil water content, which was the same tendency as the other soils. (2) The thermal conductivity of the soils was about 0.2～0.3 Wm(-1)K(-1) smaller than volcanic ash soils, and it showed the same tendency as leaf mold

Estimation of actual evapotranspiration in 3 river basins in Okayama prefecture - Comparison of Morton method and modified Brutsaert & Stricker method -

In the study, the actual evaporation was estimated in the Asahi River, the Takahashi River, and the Yoshii River basins in Okayama prefecture for four years from January 1999 to December 2002. The Morton method and the modified Brutsaert and Stricker (B & S) method were applied to the three river basins to estimate the actual evapotranspiration and compare the two methods. As a result, the actual evapotranspiration by the Morton method was all almost equal to that by the Penman’s potential evapotranspiration, and the evapotranspiration was overestimated rather than the actual evapotranspiration. The actual evapotranspiration by the modified B & S method was below the Penman’s potential evapotranspiration throughout the year, and the total annual amount was about 80% of the potential evapotranspiration. In addition, the modified B & S method showed the general tendency that the actual evapotranspiration was lower in urban area than in the hilly and mountainous areas

The Impacts of Land-Use Input Conditions on Flow and Sediment Discharge in the Dakbla Watershed, Central Highlands of Vietnam

The main objective of this study was to evaluate various land-use input conditions in terms of the performance improvement found in consequent flow and sediment simulations. The soil and water assessment tool (SWAT) was applied to the Dakbla watershed from 2000 to 2018. After the calibration and validation processes, dissimilar effects between the input conditions on the flow and sediment simulations were confirmed. It was recognized that the impact of the land use on the sediment simulation was more sensitive than with the flow simulation. Additionally, through monthly evaluation, the effects against the flow and sediment in the rainy season were larger than those in the dry season, especially for sediment simulation in the last three months from October to December. Changing land-use conditions could improve flow and sediment simulation performance better than the performance found with static land-use conditions. Updated land-use inputs should be considered in simulations if the given land-use condition changes in a relatively short period because of frequent land-use policy changes by a local government

Long-term Change Trend of Climate at Aomori City

Characteristics of long-term change for air temperature, precipitation and snowfall-depth at Aomori city were analyzed with data during the 111 years, from 1886 to 1996. The typical results were as follows: (1) The increasing rate of the annual mean air temperature was 1.07℃/111 year. (2) The increasing rate of the monthly minimum air temperature was larger than that of the monthly maximum air temperature. (3) The increasing rate of the monthly air temperature was large from winter to spring, however, was not so from summer to autumn. (4) The decreasing rate of annual precipitation was 0.187 mm/year. (5) The 5-year moving average of annual snowfall-depth might indicate the existence of about 10-year period