GAEZ FAQ


Frequently Asked Questions

What is Global AEZ about?

The term AEZ refers to the Agro-Ecological Zones system, developed by the Food and Agriculture Organization of the United Nations (FAO) in collaboration with the International Institute for Applied Systems Analysis (IIASA). The approach enables rational land-use planning on the basis of an inventory of land resources and an evaluation of their biophysical limitations and potentials for crop production.

The AEZ programs utilize the land resources inventory to assess all feasible agricultural land-use options and to quantify expected production of cropping activities relevant in a particular agro-ecological context, for specified management conditions and levels of inputs. The characterization of land resources includes all relevant components of climate, soils and landform, which are basic for the supply of water, energy, nutrients and physical support to plants.

Recent availability of digital global databases of climatic parameters, topography, soil and terrain, and land cover has allowed for revisions and improvements in calculation procedures of AEZ crop suitability and land productivity potentials, and for expanding the geographical scope to temperate and boreal environments. This effectively enabled global coverage for AEZ assessments of agricultural potentials, and it has led to this Global AEZ study.

What does AEZ produce that is not already known?

AEZ provides a standardized framework for the characterization of climate, soil and terrain conditions relevant to agricultural production. It identifies crop-specific limitations of climate, soil and terrain resources in a consistent and empirically founded way. It systematically computes spatial and temporal data on maximum potential and attainable crop yields as well as expected sustainable agricultural production potentials at different specified levels of inputs and management conditions.

The AEZ computations were completed for a range of climatic conditions, including a reference climate (average of period 1961-1990), individual historical years of 1960 to 1996, and scenarios of future climate based on the published outputs of various global climate models. Hence, the AEZ results consistently quantify impacts on land productivity of historical climate variability as well as of potential future climate change.

The FAO/UNESCO Digital Soil Map of the World (DSMW) has been made the reference for constructing a land surface database comprising of more than 2.2 million grid-cells at 5’ latitude/longitude within a raster of 2160 rows and 4320 columns. On the input side, the key components of the database applied in AEZ include the FAO DSMW and linked soil association composition table, a slope distribution database, and a layer providing distributions in terms of eleven aggregate land-cover classes derived from a global 30 arc-second latitude/longitude seasonal land cover data set. On the output side, many new data sets have been compiled, including general agro-climatic characterizations of temperature and moisture profiles, time-series of attainable crop yields for all major food and fiber crops, quantification of climate, soil and terrain constraints to crop production, and estimation of land with cultivation potential under rain-fed and irrigation conditions.

Does Global AEZ take account of socioeconomic conditions?

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. Heavy population pressure and the related increased competition by different types of land users have emphasized the need for more effective land-use planning and policies. Rational and sustainable land use is an issue of great concern for preserving the land resources for the benefit of present and future populations.

Land use is largely conditioned by environmental factors such as climate, topography, bio-diversity and soil characteristics, and determined by demographic, socioeconomic, institutional and political factors, such as education, poverty, land tenure systems, markets, and agricultural policies.

Global AEZ makes only limited use of socioeconomic information, namely for defining the input-output relationships under which individual crops are assumed to be grown. Such 'packages' are referred as land utilization types. Their evaluation results in a database of viable land use options.

As an extension of basic land productivity assessments, FAO and IIASA have developed AEZWIN, an MS-Windows application for use in national and sub-national resource planning. When evaluating the performance of alternative land utilization types, often the specification of a single objective function does not adequately reflect the preferences of decision-makers, which are of a multi-objective nature in many practical problems dealing with resources. Therefore interactive multi-criteria model analysis has been introduced and applied to the analysis of AEZ models. It is at this level of analysis that socioeconomic considerations can effectively be taken into account.

AEZWIN features modules for data management, land suitability and land productivity assessment, and multiple-criteria model analysis tools for land use optimization. A user-friendly interface with on-line tutorial has been implemented to facilitate an interactive planning process.

How does Global AEZ deal with irrigation?

The Global AEZ model allows to assess potential crop suitability for the combination of rain-fed and irrigated crop cultivation. For the assessment of irrigated land productivity potentials, it has been assumed that water resources of good quality are available and irrigation infrastructure is in place.

The assessment systematically identifies areas where climate, soils and terrain permit irrigated crop cultivation. However, AEZ does not undertake a quantification of water availability within a watershed. As working hypothesis we have considered for irrigation only those soils in arid environments which indicate possible availability of surface or groundwater resources. These soils are Fluvisols, which by definition are regularly flooded, and Gleysols, which indicate regular occurrence of high groundwater tables. The results have been used to highlight regions where the use of irrigation would result in substantial increases of potential production.

As an extension of basic land productivity assessments, FAO and IIASA have developed AEZWIN, an MS Windows application for use in national and sub-national resource planning, based on interactive multi-criteria model analysis of AEZ models. Work has been initiated at IIASA to extend AEZ-based planning models such that water supply constraints in a watershed can be taken into account in the decision analysis.

How realistic are the AEZ procedures for multiple cropping systems?

For the assessment of crop productivity from multiple cropping we created a multiple cropping zones classification based on the evaluation of thermal and moisture profiles in a grid-cell. This classification was used to determine sequential crop combinations, which are meaningful in agronomic terms. A crop combination is considered only when each individual crop is suitable, and when members can be combined in a sequential manner within the available growing period. The algorithm used for constructing cropping patterns has been designed to ensure that typical crop sequences are selected. For instance, in the typical double-cropping areas around Shanghai, the algorithm would, for example, select a long-cycle rice or maize crop as summer crop, and winter wheat or barley as winter crop.

Do the AEZ estimates account for production sustainability?

Yes, environmental sustainability is accounted for in AEZ.

Sustainable agricultural production of land is concerned with preventing erosion of topsoil and decline of fertility. Usually this is achieved by combining special crop management and soil conservation measures. In the short term, cultivation of steep slopes might lead to yield reductions due to loss of applied fertilizer and fertile topsoil. In the long term, this will result in losses of land productivity due to truncation of the soil profile and consequently reduction of natural soil fertility and of available soil moisture. Therefore, in the Global AEZ model steep slopes are declared unsuitable by setting slope limits depending on rainfall intensity and land utilization type.

Furthermore, many soils, in their natural state, in particular in the tropics, cannot be continuously cultivated without undergoing degradation. A decrease in crop yields and a deterioration of soil structure mark such degradation of nutrient status and other physical,chemical and biological attributes. Under traditional low input farming systems,this deterioration is kept in check by alternating some years of cultivation with periods of fallow. In Global AEZ, therefore, depending on climate and soil conditions, crop-type grown, and inputs applied, appropriate fallow factors are imposed to ensure maintenance of soil fertility.

How robust are the Global AEZ results?

Various modes have been pursued for ‘ground-truthing’ and verifying results of the Global AEZ suitability analysis. Apart from consulting expert knowledge and agricultural research institutes, results have been compared with available research data and agricultural statistics.

Where more detailed and compatible resource inventories are available from regional and national studies, these have been used for comparison. For instance, for China multiple linear regression was applied for estimating current arable land as a function of AEZ land suitability for irrigated and rain-fed production. Results at both province and county levels showed remarkably close relationships between current distribution of cropland and areas adjudged highly suitable for crop production in AEZ.

Nevertheless, global data sets used as inputs to AEZ are known to be of uneven quality and reliability. Hence, 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.

Who are the users of AEZ outputs?

We believe that Global AEZ provides comprehensive information relevant for decision-making. It is of particular interest to national and international organizations dealing with aspects of agriculture, land and water resources, food security, agricultural development and policies, or with climate variability and climate change. Global AEZ outputs and procedures can be beneficially applied for teaching and research, enabling comparative regional analysis and promoting an enhanced level of resource literacy.

Will there be sufficient land for agricultural production to meet the food and fiber requirements of future populations?

When considering current climate and all crop types (excluding silage maize, forage legumes and grasses) modeled in Global AEZ, and optimizing across all three input levels, we conclude that a little more than one-quarter of the global land surface (excluding Antarctica) can be regarded as sufficiently suitable for crop cultivation. For the developed countries this amounts to about one-fifth and for developing countries to about 30 percent of their respective land surfaces. This gross estimate of land with cultivation potential is twice the area that was actually in use for cultivation during 1994-96 according to FAO’s statistical data.

By looking at all possible crop types, without consideration of the actual demand for different products, we may well overestimate the 'useful' extents of land with cultivation potential. Therefore, results were also compiled by restricting the considered crop types to the three major cereals, namely wheat, rice, and grain maize. Under these assumptions, a gross estimate of about 2.5 thousand million ha of land with rain-fed cultivation potential was obtained. Of these, 0.9 thousand million ha were found in developed countries and 1.6 thousand million ha in developing countries.

Despite this hopeful aggregate picture, there are also reasons for profound concerns. Several regions exist, where the rain-fed cultivation potential has already been exhausted, as for example is the case in most parts of Asia. Land degradation, if continuing unchecked, may exacerbate regional land scarcities. Concerns for the environment and other demands for land may prevent some potentially suitable resources from being developed for agriculture. Global warming may alter the condition and distribution of land suitable for cropping. In addition, socioeconomic development may irreversibly infringe on the current agricultural resource base.

It should be noted that the above estimates refer to gross availability of suitable land. We did not subtract land required for non-agricultural uses, such as infrastructure and settlements, nor legally protected areas. In reality, therefore, some 10 to 30 percent of the suitable land may not be available for cultivation due to these other uses.

Also, we do not hesitate to state that the presently cultivated land at global scale is not likely to increase very much. Improvements in input use and technology are expected to result in higher average per hectare output from current arable land, especially in developing regions where the gap between actual and potential yields is still very wide. There is widespread under-utilization of arable land in developed regions (e.g., in Europe and United States); and, of course, there will be competition with various non-agricultural uses. In fact, a major expansion of cultivated land would also not be desirable for environmental reasons, because of obvious implications for bio-diversity and the global biogeochemical cycles (such as global carbon and nitrogen cycles). On the other hand, the current trends in population levels and consumption of some developing regions will require additional land to be brought into agricultural production, above and beyond expected increases in supply due to technological improvements and changes in international trade.

Where are shortages of agricultural land and where is room for agricultural expansion?

When we compare the results of the estimations of land with good cultivation potential combined for rain-fed wheat, grain maize and rice, with statistical data of FAO (for years 1994-96), then the following picture emerges:

A slightly negative land balance (i.e., land actually in crop cultivation exceeds the potential for rain-fed wheat, rice, or grain maize) is found in Western Asia (about 4 %), Central Asia (almost 8%), South Asia (almost 10 %), Southeast Asia (about 3%) and East Asia (about 2 %). On the other hand, considerable positive land balances are found in Eastern Europe (almost 20%), South America (about 23%), Eastern Africa (about 24%) and Middle Africa (also about 24%).

Is the land under forest ecosystems potentially good agricultural land?

The extent of land with cultivation potential presently under forest ecosystems was estimated by overlaying a current land cover database onto land with rain-fed cultivation potential. This revealed that some 464 million hectares of land with cultivation potential for wheat, rice, or grain maize coincide with land classified as dominantly forest ecosystem. This represents 1.6 percent of the area globally classified as dominantly under forest ecosystems, and it accounts for 19.1 percent of land with cultivation potential for at least one of the three cereals.

Rather wide variations occur between regions. In the Russian Federation, for example, less than 9 percent of the land dominantly under forest ecosystems is adjudged cultivation potential for cereal crops. Yet, this equates to almost 27 percent of the land with rain-fed cereal cultivation potential. In South America the respective shares are 27 and 35 percent, and in North America respectively 20 and 39 percent.

When looking at the best suitability classes only (termed very suitable (VS) and suitable (S) land in AEZ), then 237 million ha (i.e., 8.5 percent) of land currently under forest ecosystems is identified as potentially prime agricultural areas. About 40 percent of this land is located in South America, altogether some 60 percent in developing regions.

What are the main physical constraints to agricultural production?

On the basis of currently available global soil, terrain and climate data, the AEZ approach estimates that more than three-quarters of the global land surface (excluding Antarctica), amounting to roughly 13.4 thousand million ha, suffer rather severe constraints for rain-fed cultivation. Some 13 percent is too cold, 27 percent is too dry, 12 percent is too steep, and about 65 percent are constrained by unfavorable soil conditions (percentages do not sum up to 100, because different constraints coincide in some locations). The analysis concludes that only 3.5 percent of the land surface can be regarded to be entirely free of constraining factors. Only for some sub-regions in Europe did the share of essentially constraint-free conditions reach 20 percent and more.

Will global warming affect agricultural potentials?

The application of a set of temperature and rainfall sensitivity scenarios revealed a modest increase of land with rain-fed cultivation potential for temperature increases up to 2ºC on global scale. With a higher temperature increase alone (i.e., without additional rainfall), extents of cultivable rain-fed land start to decrease. When both temperature and rainfall amounts increase, then the extents of cultivable rain-fed land increases steadily. For example, a temperature increase of 3ºC paired with a rainfall increase of 10 percent, would lead to about 4 percent more cultivable rain-fed land globally. In the developed countries this increase is even markedly higher; it exceeds 25 percent. Contrariwise, for developing countries there would be a decrease of 11 percent.

In addition, a number of climate change experiments with AEZ have recently been conducted based on the outputs of various global climate models. A detailed report with results of these simulations on AEZ crop suitability and productivity is in preparation.

Apart from assessments related to agricultural production potentials, what else can Global AEZ do?

Beyond the traditional use of AEZ for mapping and quantifying crop production potentials, there are several recent applications where AEZ or outputs from AEZ analysis have been used for environmental and economic assessments.

AEZ and land evaluation for forestry: With an increased emphasis on multiple use forestry, agro-forestry, on forest as renewable energy source, and on the role of forests in global CO2 balances, the scope of quantitative land evaluation for forestry is widening.

In a recent IIASA study covering the territory of the Former Soviet Union, the AEZ evaluation procedures have been extended for the calculation of potential tree biomass. Three different types of forest resources management and exploitation were assumed. The first type, termed “conservation forestry ”, aims at nature conservation, bio-diversity preservation and limited selective extraction of individual trees. The second type reflects traditional forestry, with the main management objectives of maximizing quality and quantity of timber production. This type is referred to as “traditional forestry”. The third type captures the fully mechanized biofuel and pulpwood production for energy generation and industrial application of pulpwood. This type was termed “biomass forestry”.

AEZ and potentials of fodder and grassland: Among the total of 154 land utilization types implemented in Global AEZ, there are 13 types concerned with fodder and grass production (six types of silage maize, alfalfa, and six generic types of grasses and pasture legumes). The methodology also includes crop coefficients for quantifying crop residues (e.g., straw) and byproducts (e.g., bran from cereals or cakes from processing of oilseeds) potentially available for animal feeding. Together these can provide comprehensive information to assessments of livestock potentials as well as of regional biomass potentials from crop and grassland sources for energy uses.

AEZ linkage to economic modeling: The AEZ land productivity assessment conducted within the Land Use Change Project (LUC) at IIASA provides a multifaceted environmental characterization of land with regard to agricultural uses. Key objectives for its development included the compilation of geographically explicit information that could be embedded within an economic model, to provide a biophysical basis for the estimation of spatially explicit agricultural production relations, and to allow consistent linkage to the modeling of the water sector, in particular the demand for irrigation water.

Agricultural production in this economic model is co-determined by the biophysical potential of land, and by the level of factor inputs (in terms of nutrients and power). Potential output is based on results generated by the AEZ model. The rationale behind this specification is that the observed actual crop output level represents a certain fraction of the biophysical potential. The results obtained in IIASA's study on China, strongly support the view that it is both possible and worthwhile to integrate information from biophysical and biogeochemical process modules within an economic model.

AEZ and land-use planning: As an extension of basic land productivity assessments, FAO and IIASA have developed AEZWIN, an MS Windows application for use in national and sub-national resource planning. When evaluating the performance of alternative land utilization types, often the specification of a single objective function does not adequately reflect the preferences of decision-makers, which are of a multi-objective nature in many practical problems dealing with resources. Therefore interactive multi-criteria model analysis has been introduced and applied to the analysis of AEZ models.


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