Understanding the spatiotemporal distribution of soil moisture in a southern Arizonan dryland

The spatiotemporal distribution of soil moisture is critical for partitioning the water, energy, and carbon cycles at a variety of scales. In drylands, soil moisture is intimately linked to rainfall recycling shown through autocorrelation with future events. In this research, we present a suite of soil moisture datasets at various scales from the Santa Rita Experimental Range in southern Arizona. Over the course of one dry and wet season we present a series of coupled soil moisture measurements at the hectare scale from volumetric, TDT, EMI, and cosmic ray probe techniques. In addition, we are able to quantify the uncertainty and support volume of each measurement type from laboratory and modeling experiments. Of particular importance, we investigate the relationship between neutron counts and average soil moisture via the neutron particle transport code MCNPx. By utilizing and understanding this key relationship, we are able to provide a global constraint to the more unconstrained EMI observations allowing us to better construct a spatiotemporal picture of infiltration, evapotranspiration, and redistribution of subsurface water around the footprint. With the improved understanding of cosmic ray probes we are closer to establishing a more formal and robust framework for coupled inversion techniques.