Spatial and temporal patterns in soil moisture variations in Oklahoma and its comparison with ETA Model

Regional spatial and temporal patterns of soil moisture were investigated using Oklahoma Mesonet (OKMesonet) heat dissipation sensor observations and ETA modeled volumetric soil moisture contents. The investigation focused only on the summer season (June to August) of 1998 at 37 Oklahoma Mesonet stations, which were selected on the basis of data quality. The 30-minute OKMesonet heat dissipation sensor temperature change and its associated matric potential estimation were downloaded from CODIAC. Modeled volumetric soil moisture contents (ETA) were extracted by selecting the node closest to each OKMesonet site. OKMesonet volumetric soil moisture contents were estimated from OKMesonet matric potentials, using a soil-water retention curve estimated from the relationship between ETA volumetric soil moisture contents versus OKMesonet matric potentials. This forces the observed data to fall within the range of modeled data and to behave like an ideal soil, thereby removing any bias that might actually exist between modeled and observed data while allowing soil water content to be plotted as a function of time. The temporal and spatial patterns of volumetric soil moisture contents and rainfall during the summer were examined for the modeled and OKMesonet observational data. Rainfall data from the ETA model were not available for this study. Volumetric soil moisture content is higher in the eastern part of Oklahoma and steadily decreases to the west. Six distinct events were always present in the modeled soil moisture content, while the number of events is spatially variable in the observed 01CMesonet soil moisture content. The OKMesonet rainfall shows a very similar pattern to volumetric soil moisture content, implying a close correlation between the two. Summer average modeled volumetric soil moisture content is about 0.3 m31m3 higher than OKMesonet soil moisture content. However, the temporal patterns of modeled and OKMesonet soil moisture content are often in good agreement. This suggests that the ETA model does not overestimate soil moisture content, but rather that the ETA generates unnaturally uniform soil moisture amounts throughout Oklahoma, which result in anomalously high volumetric soil moisture contents in the ETA model.hydrology collectio