VIC Global Hydrologic Simulations

Background

1. Bart Nijssen, Reiner Schnur, and Dennis P. Lettenmaier, 2001: Global Retrospective Estimation of Soil Moisture Using the Variable Infiltration Capacity Land Surface Model, 1980-93, Journal of Climate, 14, 1790-1808.
2. Bart Nijssen, Greg O'Donnell, Dennis P. Lettenmaier, Dag Lohmann, and Eric F. Wood, 2001: Predicting the Discharge of Global Rivers, Journal of Climate, in press. (download preprint)
3. Bart Nijssen, Greg M. O'Donnell, Alan F. Hamlet, and Dennis P. Lettenmaier, 2001: Climatic Change, in press. (download preprint)

• The model forcing data set for the period 1979-1993 described in the first paper.
• The model derived variables from the first paper (evapotranspiration, soil moisture storage, runoff, snow water equivalent, and total terrestrial storage). Note that these values are uncalibrated.
• The model derived variables from the second paper. In this study selected soil parameters were calibrated using streamflow observations for a number of large river basins.

Data Sets

Variable Descriptions

• Meteorological Forcings

  Precipitation

  Daily precipitation in mm based on station observations where available. In data sparse areas observations were filled in using a stochastic procedure. Monthly means were scaled to monthly time series from other sources.

  Minimum Temperature

  Daily minimum temperature in degrees C. Based on station observations where available. In data sparse areas observations were filled in using a stochastic procedure. Monthly means were scaled to monthly time series from other sources.

  Maximum Temperature

  Daily maximum temperature in degrees C. Based on station observations where available. In data sparse areas observations were filled in using a stochastic procedure. Monthly means were scaled to monthly time series from other sources.

  Wind Speed

  Daily wind speed in m/s from the NCAR/NCEP Reanalysis Project.

  Vapor Pressure

  Mean daily vapor pressure in Pascals. This is calculated based on the daily minimum temperature, precipitation and shortwave radiation according to Kimball et al..

  Shortwave Radiation

  Mean daily incoming shortwave radiation in W/m². Calculated based on day of year, latitude, daily temperature range, precipitation and humidity according to Thornton et al..

  Net Longwave Radiation

  Mean daily net longwave radiation in W/m². This is calculated based on air temperature and humidity according to Bras et al..
  
  Caution: Most land surface schemes will take downwelling longwave radiation as an input and will calculate the outgoing longwave. When operated in water balance mode, the VIC model uses net longwave and makes the assumption that averaged over a day the land surface temperature equals the air temperature. In case snow is present an internal correction is made in the VIC model to account for this effect. However this is NOT reflected in the longwave radiation values reflected here. In many ways it would likely be better for the user to calculate the downwelling longwave directly from the other forcing data or to obtain it from an independent source.

• Model derived variables

  Evapotranspiration (model derived)

  Total evapotranspiration in mm/day. This is the entire latent heat flux, including evaporation from bare soil and interception storage, transpiration by vegetation, and sublimation from snow.

  Runoff (model derived)

  Total runoff produced within each grid cell in mm/day.

  Snow Water Equivalent (model derived)

  Amount of water stored as snow in mm.

  Soil Moisture Storage (model derived)

  Amount of water stored in the top two soil layers in mm.
  
  Note: In the uncalibrated run the soil depths were the same in all model cells. However, in the calibrated model run grid the soil depth varied by region. This effect is also present in the soil moisture amounts of the calibrated model run. To compare the modeled soil moisture storage amount around the world it would be wise to normalize by the values using the model soil depths.

  Total Storage (model derived)

  Total amount of moisture stored in a model grid cell in mm. This included water stored in all three soil layers, intrerception storage and water stored as snow.

• Miscellaneous

  Land sea mask

  Mask file that indicates a 1 for every cell that was modeled as a land surface cell. The other cells were set to the missing value as defined in the NetCDF file. There are 3462 land surface cells in the mask.

  Depth of top two soil layers

  Combined depth of the top two soil layers in m. For the uncalibrated case this is 1.0 m for all grid cells.

  Storage Capacity of top two soil layers

  Combined storage capacity of the top two soil layers in mm. This is the product of the porosity and the soil depth (in mm). This can be used in combination with the soil moisture storage to determine a soil moisture content.

Model Forcing Data, 1979-1993

Year	Meteorological Variable
	Precipitation	Minimum Temperature	Maximum Temperature	Wind Speed	Vapor Pressure	Downward Shortwave	Net Longwave
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
Monthly 1979-1993

Model Derived Variables, 1980-1993 (uncalibrated, see paper 1)

Year	Derived Variable
	Evapotranspiration	Runoff	Snow Water Equivalent	Soil Moisture Storage	Total Storage
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
Monthly 1980-1993

Model Derived Variables, 1980-1993 (calibrated, see paper 2)

Year	Derived Variable
	Evapotranspiration	Runoff	Snow Water Equivalent	Soil Moisture Storage	Total Storage
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
Monthly 1980-1993

Miscellaneous Data

Data set	Download
Land-sea mask
Depth of the top two soil layers (uncalibrated - paper 1)
Storage capacity of the top two soil layers (uncalibrated - paper 1)
Depth of the top two soil layers (calibrated - paper 2)
Storage capacity of the top two soil layers (calibrated - paper 2)

References