The IIASA database for mean monthly values of temperature

A database for current climate for a global terrestrial grid has been created using weather records from many different sources. Average monthly temperature, precipitation, and cloudiness values are included in the data set. The weather records were mostly constrained to include at least five observational years from the period 1931-1960. In order to achieve reliable data coverage in regions with especially sparse data, this constraint was not always strictly adhered to. The selected weather records were interpolated onto a grid with a resolution of 0.5° longitude and latitude using a triangulation network followed by smooth surface fitting. Temperature values were corrected to mean sea level; using an estimated moist adiabatic lapse rate and a global topography data set. This technique has enhanced the quantity of the data set, especially for temperature in data-sparse mountainous areas. Precipitation was not corrected, due to more complex relationships between precipitation and altitude. The cloudiness data set, defined as the number of recorded bright sunshine hours as a percent of its potential number, is based on fewer stations and often derived from estimated rather than computed data. Although the major annual cloud dynamics are shown, the regional reliability of the data is low. The final data base can be improved by including more weather records and by using local correction methods, especially for precipitation. The final data set is considered appropriate for use in agricultural, geographical, biogeographical and ecological studies.