Hijmans et al. 2005

Hijmans RJ, Cameron SE, Parra JL, Jones PG, Jarvis A. 2005. Very high resolution interpolated climate surfaces for global land areas. International Journal of Climatology 25: 1965-1978.

These authors describe the release of the WorldClim database, which includes data on several climate variables for a very large number of grid squares on land surfaces on Earth. Each grid square is 30 arc-seconds across, thus at the equator these squares are 0.816 square kilometers, and smaller (finer resolution) at higher latitudes.

Data for this database come primarily from weather stations located worldwide. Altitude was estimated from a Shuttle radar mission, for all latitudes south of 60°N, and excluding Antarctica. Each grid square’s climate was estimated by a complex interpolation algorithm that is analagous to regression: it fits a continuous surface to the points, but does not necessarily go through each point.

The authors describe some of the potential sources of error in the dataset, and urge higher quality data for future updates, for example by confirmation of precise locations for weather stations, and greater standardization in weather station record-keeping and reporting.

The database can be downloaded in a variety of formats from http://www.worldclim.org/. Most files are designed for use with GIS programs. A range of biologically meaningful data (maximum and minimum temperatures per year, seasonality) have been made available as well.