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Due to the tendency of soil moisture content to rapidly change over time, and because the distribution of soil moisture is often highly heterogeneous, it is important to monitor hydrodynamic processes with both a high temporal and high spatial resolution. Geophysical monitoring provides high levels of spatial resolution in soils, while the measurement frequency can allow diurnal or sub-diurnal assessment of soil moisture. Electrical methods, such as Electrical Resistivity Tomography (ERT) are ideally suited to monitor soil moisture due to the sensitivity of electrical geophysical techniques to the water content of soils. We use PRIME-a low-cost, low-power, ERT monitoring instrument developed by the British Geological Survey-to make daily measurements of soil resistivity at three agricultural observatories in southern Africa over several years, from which we can infer soil moisture changes over the study period. We use …