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This dataset presents a first attempt to estimate the volume of water required for the maintenance of freshwater-dependent ecosystems at the global scale.

Map description and dataset provided by: International Water Management Institute (IWMI)

DescriptionEnvironmental Water Requirements

Fraction of mean annual flow requirement to maintain a river basin in some agreed ecological condition.


The total environmental water requirement consists of ecologically relevant low-flow and high-flow components and depends on the objective of environmental water management. Both components are related to river flow variability and estimated by conceptual rules from discharge time series simulated by a global hydrology model.


The dataset for this map was provided by: Vladimir Smakhtin, International Water Management Institute (IWMI)


Approximately 20 to 50 percent of the mean annual river flow in different basins needs to be allocated to freshwater-dependent ecosystems to maintain them in fair condition. This is unlikely to be possible in many developing countries in Asia and North Africa, in parts of Australia, North America, and Europe, where current total direct water withdrawals (primarily for irrigation) already tap into the estimated environmental water requirements.


Please cite this map as: "GWSP Digital Water Atlas (2008). Map 71: Environmental Water Requirements (V1.0). Available online at http://atlas.gwsp.org."

Contact Information

Vadimir Smakhtin ( This e-mail address is being protected from spam bots, you need JavaScript enabled to view it ), International Water Management Institute (IWMI), PO Box 2075,Colombo ,Sri Lanka. Tel (direct): +94 11 2880055, Fax:+94 11 2786854

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