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Definitions

Dry and Sub-humid Lands

Dryland, Mediterranean, arid, semi-arid, grassland and savannah ecosystems

Hyper-arid ecosystems

Precipitation/potential evapotranspiration (P/PET) ratio of less than 0.05

Arid and semi-arid ecosystems

Arid - Precipitation/potential evapotranspiration (P/PET) ratio is greater than or equal to 0.05 and less than 0.20

Semi-arid - Precipitation/potential evapotranspiration (P/PET) ratio is greater than or equal to 0.20 and less than 0.50

Mediterranean ecosystems

No single climatic or bioclimatic definition of these areas has been developed. They generally refer to areas with cool, wet winters and warm or hot summers.

Grassland and savannah ecosystems

Grassland - Loosely defined as areas dominated by grasses (members of the family Poaceae excluding bamboos) or grass-like plants with few woody plants. Natural grassland ecosystems are typically characteristic of areas with three main features: periodic drought, fire, and grazing by large herbivores.

Savannah- Tropical ecosystems characterized by dominance at the ground layer of grasses and grass-like plants. They form a continuum from treeless plains through open woodlands to virtually closed-canopy woodland with a grassy under-storey.

  • United Nations
  • United Nations Environment Programme