ORIGINAL PAPER Estimation of ground water content using water balance and regression approach A. A. Alabi 1 & O. D. Akinyemi 1 & J. A. Olowofela 1 & F. K. Salako 2 & G. A. Ajiboye 2 & O. T. Olurin 1 Received: 16 November 2016 /Accepted: 20 September 2018 # Saudi Society for Geosciences 2018 Abstract Near-surface water content (NSWC) is a variable in space and time that significantly affect physical processes. The complex interactions between the atmosphere and the surface as well as between the surface and underground, which results in exchange of energy and moisture at quantities varying with time, make it difficult to estimate the NSWC. The traditional techniques of measuring NSWC give point data that does not represent the spatial profile. In this work, attempt was made to estimate the NSWC of an area in Abeokuta using water balance and regression approach. The study was carried out at Akole, Oke-Ata, Abeokuta, Nigeria. NSWC were measured hourly at depths 2 cm, 50 cm 100 cm, 150 cm, and 200 cm between 1 January 2014 and 31 December 2014 using Decagon EM50 data logger. Daily air temperature, solar radiation, relative humidity, and precipitation data for the location were obtained from the Nigerian Metrological Agency. Water balance approach combines empirically only the air temperature and precipitation readings to estimate NSWC. Regression approach employed the knowledge of water content at the surface or near the surface layer to estimate NSWC at other depths. Models were tested by Nash–Sutcliffe (NS) efficiency and coefficient of determination (R 2 ), estimated NSWC using water balance approach was in good agreement with measured data at depths of 2, 50, 100, and 200 cm with R 2 of 0.9091, 0.9166, 0.8540, and 0.7139 respectively. NSWC estimated with regression approach was reasonably close to observed values at depths of 50, 100, 150, and 200 cm with R 2 of 0.9881, 0.8567, 0.6418, and 0.6278 while the NS were 0.6394, − 0.8132, − 3.5785, and 0.3642 respectively. The NS value of 0.6394 shows that the model performed creditably well at the depth of 50 cm only. The high and consistently positive values of NS efficiency revealed that water balance approach was better than the regression approach in estimating NSWC. Keywords Near-surface water content . Air temperature . Precipitation . Water balance and regression approach Introduction The amount of water in the soil is an important variable in hydrology; it is the parameter that treadles the proportion of rainfall that percolates, runoff, or evaporates from the land (Jackson et al. 1999). An operational capability to estimate the temporal variation and spatial distribution of the near- surface water profiles is applicable in improving weather and erosion predictions through developed modeling of the interaction of land surface processes (Fast and McCorcle 1991; Engman 1992; Betts et al. 1994; Su et al. 1995) and through upgraded hydrological modeling (Beecham 1995; Western et al. 1997). Others benefits include efficient water management through rational irrigation planning (Jackson et al. 1981, 1982, 1987; Saha 1995), improved crop yield through optimal soil water conditions before planting and dur- ing the growing period (Topp et al. 1980; Jackson et al. 1987; Saha 1995). Estimation of NSWC is also helpful in monitor- ing of global climate change and maintenance of global heat balance through the persistence of high or low soil water con- tent (Engman 1992) and soil denitrification (Axelsson et al. 1990) respectively. Understanding the dynamics and variability of soil water content is crucial to the perception of the role of the hydro- logical cycle in climate (Entekhabi et al. 1999) and a variety of ecological and biogeochemical processes. Water balance approach combined three components; precipitation, * A. A. Alabi derylab@yahoo.com 1 Department of Physics, Federal University of Agriculture, Abeokuta, Nigeria 2 Department of Soil Science and Land Management, Federal University of Agriculture, Abeokuta, Nigeria Arabian Journal of Geosciences (2018) 11:659 https://doi.org/10.1007/s12517-018-3935-2