Using the U.S. Climate Reference Network to develop Gridded Soil Moisture Products over the Conterminous United States

Since regions of drought and excessive rainfall can have important socio-economic impacts, more accurate analysis and prediction of these extreme conditions will help mitigate adverse effects to the public and private communities. The US Climate Reference Network (USCRN) consists of 114 weather stations located across the coterminous United States. All stations use highly-accurate instruments to measure air temperature, surface temperature, solar radiation, relative humidity, precipitation, wind, soil temperature, and soil moisture. Installation of the soil moisture sensors was completed in 2011. In this study, we develop a technique to use the USCRN stations as “anchor points” to characterize soil moisture conditions as a function of soil and vegetation properties and precipitation. These relationships are then used along with high-resolution gridded datasets to create a spatially expanded soil a Soil Moisture Analysis Model Product (SWAMP).

To produce SWAMP, the 4-km Parameter-elevation Relationships on Independent Slopes Model (PRISM) precipitation (Pr) and Atmosphere-Land Exchange Inverse model (ALEXI) evapotranspiration (ET) grids are used as forcing functions.
These water inputs and outputs are used along with the observed USCRN soil moisture and precipitation values to obtain relationships between soil moisture and Precipitation/ET for 16 unique soil/vegetation categories. The relationships between soil/vegetation and Pr/ET at each USCRN station can be used as a proxy at all other 4-km gridpoints that do not contain a USCRN station, but have the soil/vegetation categories representative of a USCRN station. Each 4 Km box has 2025 90 m grid points for soil/vegetation type. By starting with initial soil moisture fields from the USCRN, soil moisture products such as the available water content and fractional available water in the upper 50 cm of the soil are produced by using the daily PRISM/ALEXI data along with the previous day’s soil moisture values and the transfer functions developed between PRISM/ALEXI and USCRN. The transfer functions will be used to modify the soil moisture values by applying weighting from a histogram of the 16 soil/vegetation categories from the 90 m subgrid information at each 4-km gridpoint. The resulting soil moisture product will be used to improve drought analysis and forecasts.