The Global AEZ results presented are based on a half-degree latitude/longitude
world climate data set (Climate Research
Unit of the University of East Anglia), 5' soils data derived from the digital
version of the FAO Soil Map of the World, the 30
arc-seconds latitude/longitude Global Land Cover Characteristics Database
(USGS Eros Data Center), and
a 30 arc-second digital elevation data set GTOPO30.
While representing the most recent global data compilations, the quality and
reliability of these data sets is known to be uneven across regions. Especially
the quality of the world soil map is reason for concern. It is based on a 1:5,000,000
scale map and it is generally accepted that its reliability may vary considerably
between different areas. At present substantial improvements to the soil information
is in progress, as for example the recent SOTER
updates for;
Another issue is that the current status of land degradation cannot be inferred from the FAO Soil Map of the World. The only study available with global coverage, the Global Assessment of Soil Degradation (GLASOD) compiled by ISRIC and UNEP, indicates that state and rate of various types of degradation might very well affect land productivity. However, the GLASOD study itself offers insufficient detail and quantification for useful application within Global AEZ.
Also the agronomic data, such as the data on environmental requirements for some crops, contain generalizations necessary for global applications. In particular assumptions on occurrence and severity of some agro-climate related constraints to crop production would, no doubt, benefit from additional verification and data.
Socioeconomic needs of rapidly increasing and wealthier populations are the main driving force in the allocation of land resources to various kinds of uses, with food production as the primary land use. For rational planning of sustainable agricultural development socioeconomic considerations are indeed crucial. So far, in Global AEZ the use of socioeconomic information is limited to the definition of modes of production and the quantification of 'input-output packages'. They are referred to as the land utilization types, taking, to some extent, into account the socioeconomic context of production decisions and conditions.
For the above reasons, the results obtained from this Global AEZ study should be treated in a conservative manner at appropriate aggregation levels, which are commensurate with the resolution of basic data and the scale of the study.
While various modes have been pursued for 'ground-truthing' and verifying results of the Global AEZ suitability analysis, there is a need for further validation of results and underlying databases.