Soil salinity

This map shows the distribution of salt-affected soils in the region. Using the Fertility Capability Classification (FCC), these soils are defined (Sanchez et al., 1982) as having ‘> 4 dS/m of electrical conductivity of saturated extract at 25°C within 1 m of the soil surface’.Within the FAO soil classification system Read more…

Relative change in annual trend precipitation 1901-2007

This map is based on the Full Data Reanalysis Product Version 4 of the Global Precipitation Climatology Centre (GPCC). It has been obtained by linear regression fitted to the 107-year time series of annual precipitation of each 0.5×0.5 degree grid cell by the least-squares method and subsequent resampling to 0.008333 degree (about 1 km) spatial resolution. The map shows the average relative change between 2007 and 1901 in percent per decade (10-year period) as measured along the trend line.
In spite of the high year-to-year variability, there is a clear and often highly significant trend, which is mostly negative (0-5% decrease/decade), with a positive increase in parts of Central Asia. Only in some of the extremely dry parts of the region, this simple linear model leads to an obvious overestimation of change (areas mapped as having 15 to over 30% relative change of annual precipitation per decade).

Population density

This map shows population density  as persons per square kilometer. The uneven pattern of large and small polygons is more a reflection of the size of the statistical units available in different countries than of the actual distribution of people.

Proportion of underweight children(year 2000)

This map shows the percentage of underweight children. As with the map of population density , the uneven pattern of large and small polygons is an artifact due to differences in the size of the statistical units available in different countries and, while offering a reasonable average, does not necessarily allow a point-exact estimate of this poverty indicator.

Length of the moisture-limited growing period

The climatic growing period is calculated by means of a model developed by the Food and Agriculture Organization of the United Nations (FAO, 1978) to estimate the length of growing period under either moisture-limiting or temperature-limiting conditions, or both. Under rainfed conditions, both moisture and temperature can be limited. Under irrigated conditions, only temperature is to be considered a limiting factor.
The moisture-limited growing period is calculated, using a waterbalance approach, as the ratio of actual evapotranspiration (AET) to potential evapotranspiration (PET). If this ratio for any particular month is higher than a user-defined threshold (in this study 0.5), that month is part of a growing period. If it is not, that month is not part of the growing period. The start date of the moisture-limited growing period is obtained from linear interpolation of the AET/PET ratios between the last month that is not part of the growing period, and the first month that is part of the growing period. The end date, inversely, is obtained by linear interpolation of the AET/PET ratios between the last month that is part of the growing period, and the first one that is not part of the growing period.

Land use/land cover 1993

This map shows  an 8-class land use/land cover map, compiled by aggregation of an initial 12-class land use/land cover classification based on image analysis of AVHRR data at 1-km spatial resolution for the period April 1992 to March 1993. The main approach used for building up the classification was a Read more…

Irrigated areas

This map shows the percentage of land that is irrigated. Whereas irrigation is the ultimate solution for agricultural water shortage, this map makes clear that only a small fraction of the drylands is irrigated, although there are major differences between individual countries (-> Statistical Tables).

Drylands and SRT types

This map shows which drylands belong to the SRT2 category (requiring vulnerability and risk reduction) and which ones to the SRT3 category (with possibilities for sustainable intensification). The subdivision is entirely based on the value of the aridity index (ratio of mean annual precipitation over mean annual potential evapotranspiration), with Read more…

Farming systems

This map differentiates 19 farming systems on the basis of the classification developed by Dixon et al (2001, see Data source). It illustrates the diversity of the production systems and their adaptation to highly diverse environments. In a general way, the agricultural systems of these regions can be subdivided into 3 groups: (a) rainfall-based systems; (b) irrigated systems; and (c) intermediate systems. The latter rely on spatially and temporally variable mixes of rain and irrigation water. Although overlap is considerable, these systems occupy specific segments of the aridity spectrum. The irrigated systems constitute the only notable exception, since they occur under all aridity regimes. As aridity increases, the diversity in agricultural systems drops. The systems also occupy an amazing range of thermal climates, ranging from tropical to temperate continental.