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Updated 12 October, 2003

US National Assessment of
the Potential Consequences
of Climate Variability and Change
VEMAP Tables of Means and Variances




The symbols are as follows:

  • modern = 1961-1990
  • 2030 = 2025-2034 for the means and 2015-2044 for the variances
  • 2095 = 2090-2099 for the means and 2070 - 2099 for the variances
  • w = December, January, February
  • s = June, July, August
  • CCC = CGCM1
  • Had = HADCM2

The following tables represent several improvements of the former tables present in the NAST report:

1.  CGCM1 values are recalculated from VEMAP release 4, which corrects for the release 3 georeferencing error.

2.  All calculations are now done seasonally for summer and winter in order to match against the corresponding maps (see  images ).

3.  Precipitation values (both means and variances) are presented as absolute VEMAP values as well as ratios and percent differences, since the precipitation values vary so much over a large region (Tables 5,6,7,8).

4.  Note that the precipitation ratios of the corresponding maps (see images) have been redone so that they represent the means of the ratios rather than the ratios of the means (which is how they were done previously).  Therefore the ratios in Table 6 do not represent the same exact ratio as represented in the maps.  However, the means and variances of precipitation (Tables 5,7) for regions are more useful if provided as means of absolute (VEMAP) precipitation rather than the means of the ratios.

5.  Time series have been detrended over each of the 30 year periods prior to calculating the variances.

6.  Variances are now provided as percentage change, i.e. ((future-modern)/future)x100 (Tables 2,4,8).

To interpret precipitation ratios (Tables 6, 9):  The ratio is the future/modern.  So if the ratio is 1.3, than the future values is a 30% increase over the modern value (i.e. modern x 0.3 + modern = future).  If the ratio is 0.8, than the future value is a 20% decrease from the modern value.  Table 8 however, is the % difference, which is (future-modern)/modern X 100.  So if the value is -30, then this means a 30% decrease.

You can obtain Excel files of the following tables by anonymous ftp to  Please see the README file for details.

All variance tables were corrected on 11/19/99 (please don't use values from before this date).

All tables were corrected on 1/25/00 to incorporate the correct NAST megaregions (NAST megaregions).  

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