You're looking for the Third Geneva Convention. Full .pdf here:
http://www.mineaction.org/downloads/...tion%20III.pdf
Skimming through, I can find nothing saying that prisoners of war have to be interred in a climate similar to where they were taken, just that
Quote:
Clothing, underwear and footwear shall be
supplied to prisoners of war in sufficient
quantities by the Detaining Power, which
shall make allowance for the climate of the
region where the prisoners are detained.
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and
Quote:
Prisoners of war interned in unhealthy areas,
or where the climate is injurious for them,
shall be removed as soon as possible to a
more favourable climate
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