The NOAA Hydrometeorology Testbed Soil Moisture Observing Networks: Design, Instrumentation, and Preliminary Results

The NOAA Hydrometeorology Testbed (HMT) program has deployed soil moisture observing networks in the watersheds of the Russian River and the North Fork (NF) of the American River in northern California, and the San Pedro River in southeastern Arizona. These networks were designed to serve the combined needs of the hydrological, meteorological, agricultural, and climatological communities for observations of soil moisture on time scales that range from minutes to decades. The networks are a major component of the HMT program that has been developed to accelerate the development and infusion of new observing technologies, modeling methods, and recent scientific research into the National Weather Service (NWS) offices and to help focus research and development efforts on key hydrological and meteorological forecast problems. These forecast problems are not only of interest to the NWS, but they also play a crucial role in providing input to water managers who work at the national, state, and local government levels to provide water for human consumption, agriculture, and other needs. The HMT soil moisture networks have been specifically designed to capture the changes in soil moisture that are associated with heavy precipitation events and runoff from snowpack during the melt season. This paper describes the strategies used to site the networks and sensors as well as the selection, testing, and calibration of the soil moisture probes. In addition, two illustrative examples of the data gathered by the networks are shown. The first example shows changes in soil moisture observed before and during a flood event on the Babocomari River tributary of the San Pedro River near Sierra Vista, Arizona, on 23 July 2008. The second example examines a 5-yr continuous time series of soil moisture gathered at Healdsburg, California. The time series illustrates the transition from a multiyear wet period to exceptionally dry conditions from a soil moisture perspective.