There's publicly available data database of aridity and PET, that is precipitation/evaporation/transpiration
http://www.cgiar-csi.org/data/global-aridity-and-pet-database
It's a raster on a 10 arc-second grid. It should be importable using a command like this
Import[ "http://exampledata.wolfram.com/ArcGRID.zip"], which works with the example data set.
But I get this error message with the (several hundred megabyte) aridity dataset downloaded to my machine.
LinkObject::linkd: Unable to communicate with closed link LinkObject['/Applications/Mathematica.app/Contents/SystemFiles/Converters/Binaries/MacOSX-x86-64/GDAL.exe',588130,13].
Import::fmterr: Cannot import data as ArcGRID format.
Any wisdom from this crowd?