The methodology is described in this peer-reviewed article:
Karger, D.N., Conrad, O., Böhner, J., Kawohl, T., Kreft, H., Soria-Auza, R.W., Zimmermann, N.E, Linder, H.P. & Kessler, M. (accepted) Climatologies at high resolution for the earth’s land surface areas. Scientific Data.
For a former version of the article see:
High resolution (30 arcsec, ~1 km)
Precipitation, Temperature, Bioclimatic variables
Monthly coverage 1979 – 2013
Incorporation of topoclimate (e.g. orographic rainfall & wind fields). Downscaled ERA-interim model. Allows calculation of derived parameters based on monthly values such as length of dry periods etc.
The dataset is in GEOtiff format. GEOtiff can be viewed using standard GIS software such as:
SAGA GIS – (free) http://www.saga-gis.org/
ArcGIS – https://www.arcgis.com/
QGIS – (free) www.qgis.org
DIVA – GIS – (free) http://www.diva-gis.org/
GRASS – GIS – (free) https://grass.osgeo.org/
All products of CHELSA are in a geographic coordinate system referenced to the WGS 84 horizontal datum, with the horizontal coordinates expressed in decimal degrees. The CHELSA layer extents (minimum and maximum latitude and longitude) are a result of the coordinate system inherited from the 1-arc-second GMTED2010 data which itself inherited the grid extent from the 1-arc-second SRTM data.
Note that because of the pixel center referencing of the input GMTED2010 data the full extent of each CHELSA grid as defined by the outside edges of the pixels differs from an integer value of latitude or longitude by 0.000138888888 degree (or 1/2 arc-second). Users of products based on the legacy GTOPO30 product should note that the coordinate referencing of CHELSA (and GMTED2010) and GTOPO30 are not the same. In GTOPO30, the integer lines of latitude and longitude fall directly on the edges of a 30-arc-second pixel. Thus, when overlaying CHELSA with products based on GTOPO30 a slight shift of 1/2 arc-second will be observed between the edges of corresponding 30-arc-second pixels.
Resolution (decimal degrees): 0.0083333333
West extent (minimum X-coordinate, longitude): -180.0001388888
Southextent (minimum Y-coordinate, latitude): -90.0001388888
East extent (maximum X-coordinate, longitude): 179.9998611111
Northextent (maximum Y-coordinate, latitude): 83.9998611111