Projected Mean Vapor Pressure (VAP) AR4 B1/A1B/A2 - Monthly

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

This data has been prepared as model input for the Integrated Ecosystem Model (IEM) and should be regarded as such. The data constitute the result of a downscaling procedure using the CMIP3/AR4 General Circulation Model (GCM) monthly time series outputs from the "CCCMA CGCM31"(~3.75 degrees spatial resolution), and "MPI ECHAM5"(~1.875 degrees spatial resolution) models under the 20c3m (historical) and B1/A1B/A2 (future) scenarios and Climatic Research Unit (CRU) TS2.0 (1961-1990,10 min spatial resolution) global climatology data.

The spatial extent includes Alaska, the Yukon Territories, and Northern British Columbia.

Methods of creating downscaled relative humidity data:

1. The GCM input data are distributed as relative humidity along with the CRU CL 2.0, therefore no conversion procedure was necessary before beginning the downscaling procedure.

2. Proportional Anomalies generated using the 20c3m Historical relative humidity data 1961-1990 climatology and the A1B Future relative humidity data (2001-2100).

3. These 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. The GCM 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 projected time series 2001-2100.

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 AIEM modeling project is 1km, so the newly created downscaled time series is resampled to this resolution using a standard bilinear interpolation resampling procedure.

7. The final step was to convert the downscaled relative humidity data to vapor pressure using the calculation below, which uses a downscaled temperature data set created utilizing the same downscaling procedure.

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