Dryland systems

Similar term(s): drylands.


Dryland systems are ecosystems characterised by a lack of water. They include cultivated lands, scrublands, shrublands, grasslands, savannas, semi-deserts and true deserts.

The lack of water constrains the production of crops, forage, wood, and other ecosystem services.

Four dryland subtypes are widely recognized: dry sub-humid, semiarid, arid, and hyperarid, showing an increasing level of aridity or moisture deficit.

Source: GreenFacts based on Millennium Ecosystem Assessment  Glossary


Drylands refer to land areas where the mean annual precipitation (P) is less than two thirds of potential evapotranspiration (PET = potential evaporation from soil plus transpiration by plants), excluding polar regions and some high mountain areas which meet this criterion but have completely different ecological characteristics.

Hyperarid areas, also referred to as true deserts, have a P/PET ratio of less than 0.05.

Arid areas have a P/PET ratio of 0.05 to 0.20.

Semiarid areas have a P/PET ratio of 0.20 to 0.50.

Dry sub-humid areas have a P/PET ratio of 0.50 to 0.65.

Source: GreenFacts, based on CBD Dry and Sub-humid Lands Biodiversity Definitions 

To read about this term in context:

GreenFacts Summary on Desertification:


Español: Tierras secas
Français: Zones sèches
Nederlands: Droge gebieden

Related publications: