Estimation of soil moisture and its effect on soil thermal characteristics at Astronomical Observatory, Thiruvananthapuram, south Kerala

Soil moisture is an important parameter of the earth’s climate system. Regression model for estimation of soil moisture at various depths has been developed using the amount of moisture near the surface layer. The estimated values of soil moisture are tested with the measured moisture values and it is found that the estimations are comparable with the observations. The variation of soil thermal properties with the amount of moisture in isohyperthermic ultisols has been investigated at a tropical site in south Kerala for the year 2008. The soil temperatures at 0.05, 0.10, 0.20, 0.30, and 0.50 m depths and soil moisture at 0.05 and 0.10 m are measured using the hydrometeorological data acquisition system installed at the observational site. For soil water contents ranging between 11 and 42% in the soil layer of depth 0.05–0.10 m, the mean values of the heat capacity, thermal diffusivity, thermal conductivity, and thermal admittance obtained were 2.2466 × 10−6 Jm−3K−1, 0.4238 × 10−6 m2s−1, 0.9658 Wm−1K−1, 2.1517 Jm−2s−1/2K−1, respectively. The magnitudes of the diurnal soil thermal parameters showed strong association with the levels of the water content. The thermal diffusivity was found to increase with the amount of soil moisture, up to about 22% of the volumetric water content, but fell as the water content further increases. Similar patterns of the soil moisture levels were noticeable both for the thermal conductivity and admittance.