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Ecoregions and climate zones (long)

I originally posted this on the Alpine list. Linda M. thought that others of
you on the Iris list might be interested.

Here is description of the KOPPEN-TREWARTHA climate system. Please note that
certain isotherms do play a significant part in this system, but that they
are not the exclusive parameter as in the USDA Plant Hardiness Zone system.

Definitions and Boundaries of Koppen-Trewartha System:

Climate group:

Tropical Humid Climates 
Ar      All months above 64 F (18 C) and no dry season
Aw      Same as Ar, but with 2 months dry in winter.

Dry Climates
BSh     Potential evaporation exceeds precipitation, and all months
         above 32F (0 C)
BWh     One-half the precipitation of BSh, and all months above 32 F (0 C)
BSk     Same as BSh, but with at least 1 month below 32 F (0 C)
BWk     Same as BWh, but with at least 1 month below 32 F (0 C)

Subtropical Climates
Cs      8 months 50 F (10 C) or more, coldest month below 64 F (18 C), and
         summer dry
Cf      Same as Cs, but no dry season.

Temperate Climates
Do      4 to 7 months above 50 F (10 C), coldest month above 32 F (0 C)
Dca     Same as Do, but warmest month above 72 F (22 C)
Dcb     Same as Do, but warmest month below 72 F (22 C)

Boreal Climates
E       Up to 3 months above 50 F (10 C)

Polar Climates
Ft      All months below 50 F (10 C)
Fi      All months below 32 F (0 C)

A/C boundary = Equarorial limits of frost; in marine locations, the isotherm of
                 64 F (18 C) for coolest month
C/D boundary = 8 months 50 F (10 C)
D/E boundary = 4 months 50 F (10 C)
E/F boundary = 50 F (10 C) for warmest month
B/A, B/C, B/D, B/E boundary = Potentential evaporation equals precipitation

Bailey, Robert G. 1995; Description of the ecoregions of the United States.
2nd ed. USDA Forest Service, Misc. Pub. 1391. 108 p.

which is based on: 

Koppen, W. 1931 Grundriss der Klimakunde. Berlin: Walter de Gruyter Co. 388 p.

as modifified by Trewartha:

Trewartha, G. T. 1968. An introduction to weather and climate. 4th ed. New
York: McGraw-Hill. 408 p.

Trewartha, g.t.; Robinson, A. H.; Hamond, E. H. 1967. Physical elements of
geography. 5th ed. New York: Mcgraw-Hill. 527 p.

Other than renaming (and numbering), Bailey made only the following major
changes to the Koppen system:

        1) Merged Koppen groups C and D into the Humid Temperate Domain
(200) and the split out the Praire as a distict climate division (250) from
Koppen types Cf, Dca and Dcb.
        2) Merged Koppen groups E and F into the Polar Domain (100).

Baily's Ecoregions (with Koppen equivalents)

100 Polar Domain
        120 Tundra Division (Koppen: Ft)
        130 Subarctic Division (Koppen: E)
200 Humid Temperate Domain
        210 Warm Continental Division (Koppen: portion of Dcb)
        220 Hot Continental Division (Koppen: portion of Dca)
        230 Subtropical Division (Koppen: portion of Cf)
        240 Marine Division (Koppen: Do)
        250 Praire Division (Koppen: arid portions of Cf, Dca, Dcb)
        260 Mediterranean (Koppen: Cs)
300 Dry Domain
        310 Tropical/Subtropical Steppe Division (Koppen: BSh)
        320 Tropical/Subtropical Desert Division (Koppen: BWh)
        330 Temperate Steppe Division (Koppen: BSk)
        340 Temperate Desert Division (Koppen: BWk)
400 Humid Tropical Domain
        410 Savanna Division (Koppen: Aw)
        420 Rainforest Division (Koppen: Ar)

Each of the above divisions are further subdivided in geographically
specific "provinces".

Though Bailey's system is in official use both by the EPA and the Forest
Service, I was forced to place numerous calls around the country to track
this pamphlet (and map) down. I finally got it by calling the Rocky Mtn.
office of the US Forest Service in Ft. Collins, CO. and leaving a voice mail
request (970) 488-1719. The raster map data is much more readily available
both on CDROM and Gopher files over the Internet, but you must have either a
UNIX box to run the GRASS Graphical Information System or Windows NT to run
the GRASSLAND GIS. If you are a techie type like me, send me an email and
I'll send you the various URL's of interest that I have located. As I don't
currently have my NT running, I cannot comment on the quality or usefulness
of this data and software.

Beth Matney <bmatney@alltel.com)
USDA zone 7b
Koppen climate group Cf
Baily's Ecoregion 231/M231 -
Subtropical Division, Southeastern Mixed Forest Province/Ouachita Mixed Forest

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