Investigation of the Relationship Between Relative Humidity and Electrical Resistivity of Soil in Calabar, Cross River State

The electrical resistivity of soil is a geophysical parameter of fundamental importance in civil engineering, agriculture, and environmental monitoring. In humid coastal environments such as Calabar in Cross River State, South South Nigeria, seasonal and diurnal variations in relative humidity significantly influence soil moisture content and consequently soil electrical resistivity. This study investigates the relationship between relative humidity and the electrical resistivity of clay-loam soil in Calabar metropolis. Relative humidity is measured at 30-minute intervals using a calibrated digital thermo-hygrometer over a 60-day period spanning both dry and rainy season conditions. Simultaneous four-electrode Wenner array resistivity measurements are performed at 20 field sites at depths of 0.5, 1.0, and 1.5 metres. Statistical regression analysis establishes a power-law relationship between soil electrical resistivity and volumetric moisture content derived from soil weight loss measurements. Results demonstrate that resistivity decreases from 280 to 42 ohm-metres as relative humidity increases from 52 to 96 percent under field conditions. The functional relationship is consistent with Archie's Law at shallow depths. The study provides empirical parameters for electrical resistivity tomography interpretation in Cross River State's coastal environment. Keywords: electrical resistivity, relative humidity, soil moisture, Calabar, Archie's Law