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Treatments of Precipitation Inputs to Hydrologic Models
- Beeson, P.C., Doraiswamy, P.C., Sadeghi, A.M., Di Luzio, M., Tomer, M.D., Arnold, J.G., Daughtry, C.S.T.
- Transactions of the ASABE 2011 v.54 no.6 pp. 2011
- Conservation Effects Assessment Project, USDA, agricultural watersheds, engineering, hydrologic models, kriging, meteorological data, prediction, rain, rain gauges, rivers, soil water, stream flow, water quality, water use, watershed hydrology, Iowa
- Hydrologic models are used to assess many water resource problems, from agricultural use and water quality to engineering issues. This study shows how the combination of rain gauges (accurate at a point) and NEXRAD precipitation data (covering a wide area) can provide accurate, timely rainfall data that can drive the Soil and Water Assessment Tool (SWAT) model, which provides a more reliable tool for producers and policy-makers alike. The treatment of rainfall data was tested in the South Fork of the Iowa River, which covers about 788 km 2 (194,720 ac) and is one of 15 benchmark watersheds of the USDA Conservation Effects Assessment Project (CEAP). The results show significant improvement in model predictions in which rainfall data were correctly modified. Gauge records with values for trace events performed better as data sources than records in which trace events were given zero value, even though the mean annual rainfall differed by < 25 mm. The combination of rain gauge and NEXRAD data provided superior results even when the watershed included a sufficient spatial distribution of rain gauges. Of the six methods used to adjust gauge and NEXRAD data, inverse distance weighting or kriging with external drift predicted streamflow among the four gauges was the best among those tested. In the absence of rain gauge data, the simple adjustment of the NEXRAD estimates to match total rainfall amounts in the region resulted in adequate streamflow estimates. This finding is important because uncorrected NEXRAD precipitation values, although only 15% below annual precipitation values, resulted in a greater than 50% difference in streamflow estimates. The choice of rainfall treatment should be considered carefully to provide accurate model predictions.