1. ReferencesAcknowledgements Funding for this work was provided by NASA grant #NNX10AQ77G S01 We would like to thank personnel at the NWS/NCRFC, and in particular Mike DeWeese, for their assistance in site identification and data collection. Identifying SNOW17 model parameters from MODIS and NOHRSC products for use in streamflow prediction models Kristie J. Franz and David Dziubanski Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA Increasingly, hydrologic modelers are interested in identifying model parameters directly from field or other types of data, rather than through the calibration process. Parameter identification for conceptual models is difficult because the values typically do not relate to real-world observations. The goal of this study is to explore whether some parameters can be adequately identified without calibration for a conceptual temperature index snow model, the US National Weather Service (NWS) SNOW17 model. In this study, we use SCA data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) and SWE data from the National Operational Hydrologic Remote Sensing Center (NOHRSC) to identify basin-specific Areal Depletion Curves (ADCs) and model parameter SI for the SNOW17 model. Anderson, E.A., 1973. National Weather Service River Forecast System-Snow Accumulation and Ablation Model. NOAA Technical Memorandum: NWS Hydro-17, US National Weather Service. Riggs, G. A., Barton, J. S., Casey, K. A., Hall, D. K., & Salomonson, V. V. (2000). MODIS Snow Products Users' Guide. http://www.snowmelt.gsfc.nasa.gov/MODIS_Snow/sugkc2.html.http://www.snowmelt.gsfc.nasa.gov/MODIS_Snow/sugkc2.html T.S. Hogue, S. Sorooshian, H.V. Gupta, A. Holz, D. BraatzA multistep automatic calibration scheme for river forecasting models. J. Hydrometeorol., 1 (2000), pp. 524–542. Study sites The focus area is five headwater basins in the upper Midwest U.S within the North Central River Forecast Center region(NCRFC). Our goal is to improve model simulations through the use of parameters derived from MODIS SCA and NOHRSC SWE that reflect actual watershed conditions better than default values. The forecast model is being tested in lumped mode. Basin Name Location ID USGS Gauging StationSize (km 2 ) Period of Record North Raccoon River at Sac City, IASCRI4548230018131959 - 2008 East Branch Pecatonica at Blanchardville, WIBCHW354330005721948 -2008 Pecatonica River at Darlington, WIDARW354325007071948 - 2008 Blue Earth River at Rapidan, MNRAPM5532000062421950 - 2008 Redwood River at Marshall, MNMMLM553150006711948 - 2008 Introduction Study Sites and Model Models Snow Model: SNOW17 Runoff Model: Sacramento Soil Moisture Accounting (SAC-SMA) model. The two models are coupled for operational forecasting. Precipitation and Temperature Rain or Snow?? Accumulated Snow Cover Energy Exchange at Snow-Air Interface Rain + Melt Ground Melt Snow Cover Heat Deficit Liquid Water Storage Transmission of Excess Water Snow Cover Outflow Areal Depletion Curve SNOW17 Processes The SNOW17 requires an areal depletion curve (ADC), which is used to determine the portion of the basin that is contributing to melt. The ADC is applied after the modeled SWE falls below the value of parameter SI (the threshold below which the basin is less than 100% snow covered) or the maximum seasonal accumulation, whichever is smaller. MODIS SCA and NOHRSC SWE data are used to determine SI. The data is then scaled according to SI to derive an ADC. Results Areal Depletion Curves MODIS-NOHRSC-based ADCs for Rapidan, MN and Sac City, IA indicated that the SWE ratio needs to be adjusted downward by approximately 0.1 - 0.2. Blanchardville and Darlington, WI displayed a similar pattern in the MODIS-NOHRSC-based ADC for SCA less than 50%. The MODIS-NOHRSC-based ADC for Marshall, MN follows the NCRFC ADC closely, with the exception occurring in the 70-90% SCA range. Simulated Discharge Calibration Period: 1997-2003. Verification Period : 2004-2008 Three Simulations: NCRFC parameters with NCRFC curve (RFC) NCRFC parameters with MODIS-NOHRSC-based ADC and SI (RFC-SI) Recalibrated parameters with MODIS-NOHRSC-based ADC and SI (SI Calibration) Verification Period: February-May, 2007 Normalized RMSE (Baseline) ( m 3 /s) RFCRFC-SISI Calibration CalVerCalVerCalVer Sac City, IA1.371.071.371.051.491.05 Blanchardville, WI0.410.530.430.550.440.58 Darlington, WI0.430.730.430.740.490.86 Rapidan, MN1.742.011.652.031.761.88 Marshall, MN1.011.571.031.701.482.00 1.Simulated discharge was relatively insensitive to changing the ADC and SI (i.e. RFC-SI uses the MODIS-NOHRSC-based ADCs and SI without recalibration of other model parameters). 2.Recalibration of the model using the MODIS-NOHRSC-based ADCs and SI parameters did not produce significant improvements in simulated discharge, except for the Rapidan site. 3.The SI calibration tended to overestimate discharge more than the RFC calibration for 3 sites. 4.SNOW17 parameters changed significantly during recalibration when upper calibration bounds were adjusted. 5.Next step: Assimilation of MODIS snow covered area (SCA) into the SNOW-17 via Ensemble Kalman Filter (EnKF) Conclusions and Next Steps