SOIL MOISTURE MEASUREMENTS AND ESTIMATION FOR DROUGHT ASSESSMENT IN NEBRASKA

From both the agricultural and rangeland ecosystem management stand point, it is crucial to understand the role of soil moisture in the sustainable management of water resources of Nebraska and to be ready for impending drought. In order to quantify the growing season demand for water, it is important to estimate evapotranspiration as it is dependant on the availability of soil moisture, which is in turn dependant on the amount and timing of preceding precipitation. Since 1998, the Automated Weather Data Network (AWDN) maintained by the High Plains Regional Climate Center (HPRCC) has monitored soil moisture continuously. Today 51 HPRCC sites in Nebraska monitor soil moisture at four depths: 10, 25, 50 and 100 cm. In addition to that, 13 Sandhills sites monitor soil moisture with the same methods as part of the Sandhills Biocomplexity Project. Data sets from these sites range from 1 to 7 years in length. We analyze the soil moisture estimates starting from 1998 to date using the hydrology model, developed by Robinson and Hubbard (1990) and verify with the measurements in order for us to identify and correct data from any sensors that are malfunctioning thus increasing the confidence levels for subsequent products used to assess past and future droughts. The results will also include the estimates of soil moisture estimation for the historical period dating back to 1900 that will be derived based on certain variables including daily temperature range, daily precipitation, calibrated estimates of solar radiation and humidity, and a climate-based wind speed in the Penman approach for estimating daily ET, thus allowing us to estimate historical soil moisture data for various ecosystems of Nebraska. This will serve as a bench mark for our efforts to expand the application of this data set for drought vulnerability and risk management studies.