The topographic and climate database is distributed on a CD with three folders containing:
- Forty ESRI ASCII grid files of elevation (DEM) and monthly mean climate for the African continent at a spatial resolution of 0.05 degrees of longitude and latitude. The climate consists of monthly mean and annual mean values of rainfall, daily minimum temperature and daily maximum temperature, approximately covering the time period 1920 to 1980.
- Three colour images of the climate source data points and forty colour images of the ASCII grid files in device independent Adobe Acrobat.
- Documentation files.
Funding for the project was provided by the Australian International Development and Assistance Bureau.
Digitising and checking of topographic and climate data formed the major portion of the work required to produce this data base. In this the authors gratefully acknowledge many willing contributors, including Fareeha Ibrahim, Helen Neave, Christy Sanders, Joseph Tabone and Karen Weinman.
The DEM and the climate grid files were originally created using spatial analysis and interpolation techniques developed at the Centre for Resource and Environmental Studies (CRES) at The Australian National University, as described by Hutchinson et al. (1996).
Version 2.0 of the database has been produced after extensive checking and correction of the locations and elevation of the source point climate data and revised interpolation analyses using Version 4.3 of the ANUSPLIN package (Hutchinson 1991,1995,2004). This package fitted elevation dependent climate surfaces to point climate data. The incorporation of spatially varying dependences on elevation is a critical factor in the accuracy of these surfaces.
The temperature surfaces have now been produced in single tiles covering the whole continent and the rainfall surfaces have now been produced in just two tiles overlapping over the equator. The surface coefficient files for rainfall have been blended so that the two rainfall surface tiles join continously along the equator.
The underlying DEM has also been revised by revising the source topographic data and applying a revised Version 5.0 of the ANUDEM elevation gridding procedure (Hutchinson 1988,1989,2011).
The climate grids were obtained by interrogating the smoothing spline surfaces in grid form using the DEM and the MTHCLIM procedure from the ANUCLIM package (Xu and Hutchinson 2011).
Both elevation and climate data were subjected to comprehensive error detection and correction procedures provided by ANUDEM and ANUSPLIN. Accurate geocoding (longitude, longitude and elevation) of climate station data was completed by consulting 1:1M topographic maps and international climate databases.
Topographic data were digitised by CRES from 1:1M scale air navigation charts covering the entire continent, augmented by miscellaneous maps at larger scales in areas where data on the air navigation charts were sparse.
The data digitised from these maps consisted of:
- All spot heights.
- Selected points on elevation contours. All significant corners on contours, consistent with an eventual final grid resolution of approximately 1 minute of longitude and latitude, were selected. Thus points on contours were not sampled at spacings closer than 1 minute.
- Selected stream lines. All streams which could be resolved on an eventual final grid resolution of 1 minute of longitude and latitude were selected. Only very minor streams on the 1:1M air navigation charts were omitted.
The standard error of the DEM ranges between about 20 and 150 metres, depending mainly on terrain roughness.
Monthly mean values of rainfall, daily minimum temperature and daily maximum temperature at a sufficient spatial density to support reliable spatial interpolation were compiled. In addition to data already obtained by CRES from miscellaneous sources, monthly climate data were acquired from research agencies including CIMMYT, FAO, East Anglia Climate Research Unit, CSIRO Division of Forestry, Texas A&M University and from the national meteorological services of Djibouti, Gambia, Ghana, Kenya, Malawi, Morocco, Nambia, Rwanda, Seychelles, Sudan, Tanzania, Uganda and Zaire.
Data were collected over all available years of record to maximise spatial coverage, subject to the condition that rainfall averages were for at least five years of record. Most data were collected between about 1920 and 1980 for both temperature and rainfall, so the fitted climates grids can be interpreted as estimates of means for the period 1920 to 1980.
The number of accurately geocoded stations for which monthly mean climate data were obtained were as follows:
- Daily minimum temperature - 1503
- Daily maximum temperature - 1498
- Rainfall - 6051
The error of the climate grids depends mainly on the accuracy of the underlying climate surfaces. In using the DEM to calculate the climate grids, the stated errors in the DEM of up to a few hundred metres make only a minor additional contribution to errors in the climate grids.
The standard errors of the temperature are about 0.5 degrees centigrade. The standard errors of the rainfall grids range between about 5 and 15 per cent, depending on data density and the spatial variability of the actual monthly mean rainfall.
- Hutchinson, M.F. 1988. Calculation of hydrologically sound digital elevation models. Third International Symposium on Spatial Data Handling, International Geographical Union, Columbus, 117-133.
- Hutchinson, M.F. 1989. A new procedure for gridding elevation and stream line data with automatic removal of spurious pits. Journal of Hydrology 106: 211-232.
- Hutchinson, M.F. 1991. The application of thin plate splines to continent-wide data assimilation. In: J.D.Jasper (ed), Data Assimilation Systems. BMRC Res. Rep. No. 27, Bureau of Meteorology, Melbourne, 104-113.
- Hutchinson, M.F. 1995. Interpolating mean rainfall using thin plate smoothing splines. International Journal of Geographic Information Systems 9: 385-403.
- Hutchinson, M.F. 2004. ANUSPLIN Version 4.3. Fenner School of Environment and Society, Australian National University, Canberra.
- Hutchinson, M.F. 2011. ANUDEM Version 5.3. Fenner School of Environment and Society, Australian National University, Canberra.
- Hutchinson, M.F., Nix, H.A., McMahon, J.P. and Ord, K.D. 1996. The development of a topographic and climate database for Africa. In: Proceedings of the Third International Conference/Workshop on Integrating GIS and Environmental Modeling, NCGIA, Santa Barbara, California. http://www.ncgia.ucsb.edu/conf/SANTA_FE_CD-ROM/sf_papers/hutchinson_michael_africa/africa.html
- Xu, T. and Hutchinson, M.F. 2011. ANUCLIM Version 6.1. Fenner School of Environment and Society, Australian National University, Canberra.