A Methodology for Examining Changes in Soil Climate Geography through Time: U.S. Soil Moisture Regimes for the Period 1971–2000

Abstract

Soil climate is the record of temporal patterns of soil moisture and temperature and is an important component of the structure of U.S. Soil Taxonomy. The U.S. Soil Survey has used the Newhall simulation model (NSM) for estimating soil climate from atmospheric climate records at weather stations since the 1970s. The current soil climate map of the United States was published in 1994 by using NSM runs from selected weather stations along with knowledge‐based hand‐drawn mapping procedures. We developed a revised soil climate mapping methodology using the NSM and digital soil mapping techniques. The new methodology is called grid element Newhall simulation model (GEN), where a coordinate system is used to divide geographic space into a grid, and each element or grid‐cell serves as a reference area for querying and organizing model input and for organizing and displaying model output. The GEN was used to make a soil moisture map of the conterminous United States (GEN‐CONUS). The GEN‐CONUS and the 1994 map were compared to each other and to two sets of weather station data from years 1961 to 1990 and years 1971 to 2000 (NCDC). Agreement between GEN‐CONUS and the 1994 map was 75.6%. GEN‐CONUS had higher agreement than the 1994 map with NSM output from NCDC data for 1961–1990 and 1971–2000 (k = 0.845 and 0.777). The GEN methodology was also used to generate a map of projected soil climate in the year 2080 for part of the Southern Rocky Mountains, predicting expansion of the Ustic and contraction of the Udic moisture regimes.