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WEAP (the Water Evaluation and Adaptation Planning system) is a model-building tool for water resource planning and policy analysis^[1] that is distributed at no charge to non-profit, academic, and governmental organizations in developing countries.

WEAP is used to create simulations of water demand, supply, runoff, evapotranspiration, water allocation, infiltration, crop irrigation requirements, instream flow requirements, ecosystem services, groundwater and surface storage, reservoir operations, pollution generation, treatment, discharge, and instream water quality. The simulations can be created under scenarios of varying policy, hydrology, climate, land use, technology, and socio-economic factors.^[2] WEAP links to the USGS MODFLOW groundwater flow model and the US EPA QUAL2K surface water quality model.

WEAP was created in 1988 and continues to be developed and supported by the U.S. center of the Stockholm Environment Institute, a non-profit research institute based at Tufts University in Somerville, Massachusetts. It is used for climate change vulnerability studies and adaptation planning and has been applied by researchers and planners in thousands of organizations worldwide.

Establishing the ‘current accounts’ and building scenarios and evaluating the scenarios about criteria are the main WEAP applications in Simulation problems.^[3]

• Sieber, J. "WEAP History and Credits". WEAP Website. Retrieved August 14, 2020.
• Matchett, E.L.; Fleskes, J.P.; Young, C.A.; Purkey, D.R. (2015). "A framework for modeling anthropogenic impacts on waterbird habits—Addressing future uncertainty in conservation planning". U.S. Geological Survey Open-File Report 2015-1017: 1–40. doi:10.3133/ofr20151017. ISSN 2331-1258.
• Esqueda, G. Sanchez-Torres; J. E. Ospina-Noreña; C. Gay-García; C. Conde (January 2011). "Vulnerability of water resources to climate change scenarios. Impacts on the irrigation districts in the Guayalejo-Tamesí river basin, Tamaulipas, México". Atmósfera. 24: 141–155. Archived from the original on 2015-06-18.
• Purkey, D.R.; Joyce, B.; Vicuna, S.; Hanemann, M.W.; Dale, L.L.; Yates, D.; Dracup, J.A. (March 2008). "Robust analysis of future climate change impacts on water for agriculture and other sectors: a case study in the Sacramento Valley". Climatic Change. 87: 109–122. doi:10.1007/s10584-007-9375-8.
• Purkey, David R.; Huber-Lee, Annette; Yates, David N.; Hanemann, Michael; Herrod-Julius, Susan (January 2007). "Integrating a Climate Change Assessment Tool into Stakeholder-Driven Water Management Decision-Making Processes in California". Water Resources Management. 21: 315–329. doi:10.1007/s11269-006-9055-x.
• Vogel, Richard M.; Sieber, Jack; Archfield, Stacey A.; Smith, Mark P.; Apse, Colin D.; Huber-Lee, Annette (May 2007). "Relations among storage, yield and instream flow". Water Resources Research. 43. doi:10.1029/2006WR005226.
• Yates, David; Sieber, Jack; Purkey, David; Huber-Lee, Annette (December 2005). "WEAP21: A Demand-, Priority-, and Preference-Driven Water Planning Model, Part 1: Model Characteristics". Water International. 30: 487–500. doi:10.1080/02508060508691893.
• Lévite, H.; Sally, H.; Cour, J. (2003). "Water demand management scenarios in a water-stressed basin in South Africa: application of the WEAP model". Physics and Chemistry of the Earth. 28: 779–786. doi:10.1016/j.pce.2003.08.025.

• Official website
• Stockholm Environment Institute-U.S. Center
• Main SEI website
• Tufts University