Agroecological Zones

Sub-Saharan Africa Agroecological zones

Sub-Saharan Africa
       AEZ Map Query Tool

Agroecological zones (AEZs) provide consolidated information on climate (including radiation, rainfall, temperature, and humidity) for the particular purpose of assessing the production potential of land for different types of (rainfed) agriculture. Many agricultural production systems, technologies and practices are often associated with specific AEZs, or their performance is relatively uniform within individual AEZs. AEZs therefore provide a useful spatial framework for, amongst other things, thinking about the potential for innovations to spill over from one country or continent to another. In HarvestChoice we often use the AEZ spatial framework to summarize and report other important agricultural measures such as production, population, extent of cultivation, and market accessibility. This provides an ecology-based division of space as opposed to reporting based solely on administrative boundaries. Specifically, we often use AEZs to identify land suitable for rainfed cultivation, in general, as well as for the production of specific crops. Suitability surfaces based on agroecological zones, soils and other terrain variables developed by IIASA/FAO (Fischer, et al. 2001) were used as input into the HarvestChoice Crop Allocation Model.

Summarizing statistics by Agroecological Zones can also help highlight areas within countries where farmers may face greater challenges related to the adoption of new technologies, and/or the ability to respond to changing or adverse climate conditions. A summary of cropped area by AEZ for Sub-Saharan Africa shows that nearly 45% of cultivated area in the tropical region falls in the more challenging arid or semi-arid zones, and only 13% of the total cropped area is in the more humid regions of the highlands where conditions both for human populations and crop production are often more favorable. The summary of rural population by AEZ for Sub-Saharan Africa indicates that just over 36% of the rural population live in the arid or semi-arid zones, and 23% live in the more favorable moist highland regions.

For more information on the use of AEZs in the evaluation of agricultural R&D see Wood and Pardey (1997), and in the evaluation of agricultural development strategies in Omamo et al. (2007). HarvestChoice has developed primers on both the assessment of Agricultural Potential and on Geographical Targeting/Segmentation and Development Domain.

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Technical Details of the HarvestChoice AEZs

The AEZs defined by HarvestChoice were created using appropriate climate layers data from IIASA/FAO combined with elevation data from Eros Data Center. The three input variables were:

• Major Climate Divisions (based on thermal regimes as defined by IIASA/FAO:2002
• Moisture zones based on Length of Growing Period (LGP)
• Temperature class based on elevation within the specific climate divisions

Resulting Classes for Agroecological Zones (AEZ)

Agroecological Zones and Irrigated Areas (circa 2000)

Specific rules on the definitions used to create each of the classes specifically for Sub-Saharan Africa.

As noted, AEZs can help determine suitability for rainfed cultivation but they do not identify areas suitable for or currently cultivated under irrigation. To derive a complete picture of agricultural practices and potential worldwide it is also necessary to account for irrigated systems.

There are a number of global datasets depicting areas equipped for irrigation. That chosen for input to the HarvestChoice crop allocation model is the FAO/University of Frankfurt's Global Map of Irrigated Areas (GMIA) (see map). At the time the input layers for the crop allocation model were last updated, GMIA Version 4.0.0 was used. The current version is 4.0.1. When the crop production model is next updated we will incorporate the most recent version of the GMIA irrigated area data.