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Streamflow Predictability

Streamflow Predictability. Sources of Predictability. Model solutions to the streamflow forecasting problem…. Historical Data. SNOW-17 / SAC. Historical Simulation. SWE. SM. Q. Past. Future.

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Streamflow Predictability

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  1. Streamflow Predictability

  2. Sources of Predictability Model solutions to the streamflow forecasting problem… Historical Data SNOW-17 / SAC Historical Simulation SWE SM Q Past Future • Run hydrologic model up to the start of the forecast period to estimate basin initial conditions;

  3. Sources of Predictability Model solutions to the streamflow forecasting problem… Historical Data Forecasts SNOW-17 / SAC SNOW-17 / SAC Historical Simulation SWE SM Q Past Future • Run hydrologic model up to the start of the forecast period to estimate basin initial conditions; • Run hydrologic model into the future, using an ensemble of local-scale weather and climate forecasts.

  4. Sacramento Soil Moisture Accounting (SAC-SMA) model Rainfall -Evapotranspiration - Changes in soil moisture storage = Runoff • Physically based conceptual model • Two-layer model • Upper layer: surface and interception storages • Lower layer: deeper soil and ground water storages • Routing: linear reservoir model • Integrated with snow17 model • Model parameters: 16 calibrated parameters • Input data: basin average precipitation (P) and Potential Evapotranspiration (PET) • Output: Channel inflow (Q)

  5. Soil Tension and Free Water

  6. Sacramento Model Structure E T Demand Precipitation Input Px Impervious Area E T Direct Runoff PCTIM ADIMP Pervious Area Impervious Area Upper Zone Surface Runoff EXCESS Tension Water UZTW Free Water UZFW E T UZK Interflow E T Percolation Zperc. Rexp Total Channel Inflow Distribution Function E T RIVA Streamflow 1-PFREE PFREE Lower Zone Free Water Tension Water P S LZTWLZFP LZFS RSERV Supplemental Base flow LZSK E T Total Baseflow LZPK Primary Baseflow Side Subsurface Discharge

  7. Model Parameters PXADJ Precipitation adjustment factor PEADJ ET-demand adjustment factor UZTWM Upper zone tension water capacity (mm) UZFWM Upper zone free water capacity (mm) UZK Fractional daily upper zone free water withdrawal rate PCTIM Minimum impervious area (decimal fraction) ADIMP Additional impervious area (decimal fraction) RIVA Riparian vegetation area (decimal fraction) ZPERC Maximum percolation rate coefficient REXP Percolation equation exponent LZTWM Lower zone tension water capacity (mm) LZFSM Lower zone supplemental free water capacity (mm) LZFPM Lower zone primary free water capacity (mm) LZSK Fractional daily supplemental withdrawal rate LZPK Fractional daily primary withdrawal rate PFREE Fraction of percolated water going directly to lower zone free water storage RSERV Fraction of lower zone free water not transferable to lower zone tension water SIDE Ratio of deep recharge to channel baseflow ET Demand Daily ET demand (mm/day) PE Adjust PE adjustment factor for 16th of each month

  8. State Variables ADIMC Tension water contents of the ADIMP area (mm) UZTWC Upper zone tension water contents (mm) UZFWC Upper zone free water contents (mm) LZTWC Lower zone tension water contents (mm) LZFSC Lower zone free supplemental contents (mm) LZFPC Lower zone free primary contents (mm)

  9. How the SAC-SMA Model Works

  10. Study site: Root River basin in MN Root River basin • Drainage area: 1593 km2 • Largely agricultural (72%), USDA • Receives 29 to 33 inches of annual • precipitation

  11. Greens Bayou river basin in eastern Texas Data for SAC-SMA • Hourly discharge data • Hourly Mean Areal Precipitation • Model running time step is hourly • Drainage area: 178 km2 • Most of the basin is highly developed • Humid subtropical climate (890-1300 mm annual rain)

  12. SMADA Basins

  13. Error Growth models • Lorenz, 1982

  14. Greens Bayou Precip forcing fields – Nov 17, 2003 tornado

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