Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 10 3 2006 10.5194/hess-10-353-2006 http://www.hydrol-earth-syst-sci.net/10/353/2006/ http://www.hydrol-earth-syst-sci.net/10/353/2006/hess-10-353-2006.html http://www.hydrol-earth-syst-sci.net/10/353/2006/hess-10-353-2006.pdf 353 368 2006-05-17 Assimilating scatterometer soil moisture data into conceptual hydrologic models at the regional scale J. Parajka V. Naeimi G. Blöschl W. Wagner R. Merz K. Scipal Institute for Hydraulic and Water Resources Engineering, Vienna University of Technology, Austria Institute of Photogrammetry and Remote Sensing, Vienna University of Technology, Austria on leave from: Institute of Hydrology, Slovak Academy of Sciences, Bratislava, Slovakia This paper examines the potential of scatterometer data from ERS satellites for improving hydrological simulations in both gauged and ungauged catchments. We compare the soil moisture dynamics simulated by a semidistributed hydrologic model in 320 Austrian catchments with the soil moisture dynamics inferred from the satellite data. The most apparent differences occur in the Alpine areas. Assimilating the scatterometer data into the hydrologic model during the calibration phase improves the relationship between the two soil moisture estimates without any significant decrease in runoff model efficiency. For the case of ungauged catchments, assimilating scatterometer data does not improve the daily runoff simulations but does provide more consistent soil moisture estimates. If the main interest is in obtaining estimates of catchment soil moisture, reconciling the two sources of soil moisture information seems to be of value because of the different error structures.