U.S. climate reference network soil moisture measurements and drought monitoring

The U.S. Climate Reference Network (USCRN) has completed the second year of deployment of soil climate instruments in the continental U.S supported by the National Integrated Drought Information System Program. As has been done with USCRN primary climate observations of air temperature and precipitation, a triplicate measurement approach has been applied in measuring soil moisture and soil temperature. Three separate plots near each station tower have been instrumented at 5, 10, 20, 50, and 100 cm depth, providing three independent measurements of soil climate at each location. Since USCRN sites are located in isolated and stable locations, they are measuring a background, non-agricultural soil climate that will be suitable for long term studies of change over time, while also allowing current conditions to be monitored in real time. A set of three measurements at each level allows for better detection of poorly performing instruments over time, and continuity during those times when an instrument is malfunctioning. Interestingly, despite their close separation, subtle variations in soil characteristics can also lead to differing climate findings in each plot, especially with regards to moisture. For the first time, an estimate of the measurement variance of soil moisture and soil temperature can be made in real time for an entire network.

By January 2011, USCRN Program will have completed the development of the second generation soil climate measurement quality control system, and will be providing additional output for drought monitoring, both in terms of measurement data and derived products. Two soil moisture visualization tools are already completed, showing moisture infiltration graphically and displaying the range of soil moisture measured at each level in the three plots at a station. While the USCRN stations are fairly sparsely distributed, they should provide an excellent baseline for large scale drought monitoring in the U.S., and establish some new approaches for future higher resolution soil climate monitoring networks.