The CLAMP datasets consist of pairs spreadsheets. Each pair consists of a file containing physiognomic data from vegetation sites and a file containing the corresponding meteorological data for that same suite of sites. Definitions of the climate variables can be found here.

Non-Gridded or Point Data

The original CLAMP meteorological calibration data files (here designated Met3arAZ and Met3brAZ) were all derived from climate recording stations within, or as close as possible to, the vegetation sites that make up the Physg3arcAZ and Physg3brcAZ leaf physiognomic calibration data files. Although in the main these station or point data represent annual averages derived from 30 years or more of observations (so-called climate 'normals'), the period of observations were not standardised to a particular 30 year interval. Moreover, vegetation sites were sometimes some distance away from the recording stations (in some cases more than 30 kms away) and adjustments had to be made for elevation differences using simple free air lapse rates (Wolfe, 1993), which was very unsatisfactory.

The number of vegetation sites representing warm temperate and tropical climates in the Physg3 data sets are fewer than is desirable and the bias towards North America and Japan means that the calibrations may not be appropriate for other regions of the world with different biogeographic histories (Kennedy et al., 2002). To add new sites with point data is increasingly problematic because agriculture and urban expansion has limited natural vegetation to remote areas where often no meteorological stations exist. Because of their limitations, point data are no longer used for the online analysis.

Gridded Climate Data

To attempt to overcome this problem new meteorological data files were developed utilizing a 0.5° x 0.5° grid of global interpolated climate data based on the compilation of New et al. (New et al., 1999) supplemented by the ERA40 re-analysis data for atmospheric temperature at upper levels. For each location, the 3-D climatology of temperature from the ECMWF re-analysis project was used to calculate the mean lower tropospheric lapse rate for each month of the year. This was on a 96 x 73 grid that was then interpolated onto a 720 x 360 grid. The New et al. (New et al., 1999) data was then corrected to the altitude of the plant site using the monthly lapse rates. This also recalculated the specific humidity. If the lapse rate corrected temperature was much colder than the original, then the relative humidity often exceeded 100%. If this was the case, the specific humidity was adjusted until the relative humidity was equal to 100%. From this the commonly returned CLAMP climate variables were calculated. A bi-linear interpolation scheme was then used to calculate the climate parameters at the exact lat/long of the site. The use of the 3-D climatology and lapse rate corrections enable a degree of altitude correction to be made for the exact location of the existing vegetation sites and any new sites that might be added to future calibration files.

The New et al. (1999) data were derived from 30 year climate 'normals' observed between 1961 and 1990. These data are therefore more consistent than the original CLAMP point data comprising the Met3ar/br files and and more likely to better reflect the climate at the location of a vegetation sample because they are interpolated from several nearby observing sites. For a more complete account of the gridded data see Spicer et al. (2009) These low spatial resolution gridded climate data have been superceded by higher resolution data and are no longer supported for the online analysis.

High Resolution Gridded Climate Data

Subsequently New et al. (2002) produced a gridded climate data on a higher resolution 10' x 10' grid (2160 x 1080 grid points) using the same suite of meteorological observations. In CLAMP we used to refer to this as High Resolution climate data (HiResGridMet), but because we now have other high resolution gridded data sets we now call it the CRU2160 dataset. The same ERA40 re-analysis adjustments were made as for the 0.5° x 0.5° dataset.

Very High Resolution Gridded Climate Data - WorldClim2

The most recent gridded climate data used in CLAMP, and one that is applied widely in ecology and biodiversity studies, is WorldClim2 published by Fick and Hijmans (2017). This gridded data uses an approximately 30" or ~1 km x 1 km grid (43200 x 21600 grid points) based on observations made between 1970 and 2000 supplemented by satellite data. Despite the very high spatial resolution that inherently encompasses a digital elevation model and attempts to reflect aspect for consistancy we apply the same localised ERA40 adjustments as for previous CLAMP datasets. A full description of data manipulation, and comparison with previous CLAMP griddedclimate data, is in preparation.

Unlike the other climate datasets that offer only 11 variables, the WorldClim2 calibration returns either 11 or 22 variables depending on user choice.