A general characterization of moisture conditions is achieved through the concept of length of growing period (LGP), i.e. the period during the year when both moisture availability and temperature are conducive to crop growth. Thus, in a formal sense, LGP refers to the number of days within the period of temperatures above 5°C when moisture conditions are considered adequate. Under rain-fed conditions, the begin of the LGP is linked to the start of the rainy season. For establishing crops, 0.4 - 0.5 times the level of reference evapotranspiration is considered sufficient to meet water requirements of dryland crops (FAO 1978-81a; 1979; 1992a). This layer is a result of the Agro-ecological Zones (AEZ) methodology for land productivity assessments and is part of the Global Agro-ecological Zoning Database.

Global Map of Irrigation Areas - Version 5 Grid with percentage of area equipped for irrigation with a spatial resolution of 5 arc minutes or 0.083333 decimal degrees. This dataset is developed in the framework of the AQUASTAT Programme of the Land and Water Division of the Food and Agriculture Organization of the United Nations and the Rheinische Friedrich-Wilhems University, Germany. The map shows the amount of area equipped for irrigation around the year 2005 in percentage of the total area on a raster with a resolution of 5 minutes. Additional map layers show the percentage of the area equipped for irrigation that was actually used for irrigation and the percentages of the area equipped for irrigation that was irrigated with groundwater, surface water or non-conventional sources of water. In details, the following products have been released and made available for download: (A) Area equipped for irrigation expressed as percentage of total area: total=aei, surface water=aeisw, groundwater=aeigw, non-conventional sources of water=aeinc (ASCII-grid); (B) Area actually irrigated expressed as percentage of area equipped for irrigation (ASCII-grid); (C) Area equipped for irrigation expressed in hectares per cell (ASCII-grid); (D) Irrigated areas v.5 (ESRI shapefile); (E) High and low resolution images (PDF); (F) Quality Assessment (Excel) Due to the map generation method, the quality of the map can never be uniform. The overall quality of the map depends heavily on the individual quality of the data for the different countries.