Historical Monthly Vapor Pressure 1km CRU TS

This set of files includes downscaled historical vapor pressure (units=hPa) at a 1km spatial scale.

This data has been prepared as model input for the Integrated Ecosystem Model (IEM). The data constitute the result of a downscaling procedure using the Climatic Research Unit's CRU TS3.x (0.5 deg spatial resolution) monthly time series and TS2.0 (1961-1990,10 min spatial resolution) global climatology data.

Two versions are provided that correspond to different versions of CRU data.
CRU TS 3.1: 1901-2009
CRU TS 3.23: 1901-2014

Methods of creating downscaled relative humidity data:

  1. The CRU TS3.x data are distributed as Vapor Pressure and were converted to relative humidity using the conversion equation from the WMO CIMO Guide (2008).

    saturated vapor pressure = 6.112 x exp (((22.46 x temperature) / (272.62 + temperature)))
    relative humidity = (vapor pressure / saturated vapor pressure) x 100
  2. Proportional anomalies were generated using the newly converted CRU TS3.x historical vapor pressure data where the climatological period used is 1961-1990.

  3. These CRU TS3.x proportional anomalies are interpolated using a spline interpolation to a 10min resolution grid for downscaling with the CRU CL 2.0 relative humidity data.

  4. CRU TS3.x proportional anomalies are multiplied by month to the baseline CRU CL 2.0 10min relative humidity climatology for the period 1961-1990. Creating a downscaled relative humidity historical time series 1901-2009.

  5. Due to the conversion procedure and the low quality of the input data to begin with, there were values that fell well outside of the range of acceptable relative humidity (meaning that there were values >100 percent), these values were re-set to a relative humidity of 95 at the suggestion of the researchers involved in the project. It is well known that the CRU data is spotty for Alaska and the Circumpolar North, due to a lack of weather stations and poor temporal coverage for those stations that exist.

  6. The desired output resolution for the IEM modeling project is 1km, so the newly created downscaled time series is resampled to this resolution using a standard bilinear interpolation procedure.

  7. The final step was to convert the downscaled relative humidity data to vapor pressure using the below conversion equation

    saturated vapor pressure = 6.112 x exp(17.62 x temperature/(243.12+temperature))
    vapor pressure = (relative humidity x saturated vapor pressure)/100

Data and Resources

Additional Info

Spatial resolution

1000 meters

Temporal extent

Start date: January 1901

End date: December 2014


The following people worked on producing this data set:

  • Michael Lindgren
  • Stephanie McAfee
  • Tom Kurkowski
Field Value
Source http://data.snap.uaf.edu/data/IEM/Inputs/historical/vapor_pressure/
Maintainer Tom Kurkowski
Version 1.0.0
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temporal-extent-begin 1901-01-15T00:00:00
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