WEAP

WEAP (Water Evaluation and Planning) Model

Criterion	Explanation
General Description	WEAP was created in 1988 with the sponsorship of the newly formed Stockholm Environment Institute (SEI). It was designed with the aim to be a flexible, integrated, and transparent planning tool for evaluating the sustainability of current water demand and supply patterns and exploring alternative long-range scenarios. Over the years WEAP has been applied in many countries and river basins. The software has been transferred to water planners throughout the world. The model website is at: https://www.weap21.org/
Model Domain	The model domain is flexible and specified by the user.
Developer	The model developer is Stockholm Environment Institute (SEI). SEI continues to support the development of WEAP through its US Center (SEI-US), which was established in 1989 and hosted by the Tellus Institute until 2006.
Hardware computing requirements	WEAP runs on all versions of Microsoft Windows from Windows XP to Windows 10, with a minimum of 256 MB of RAM and 100 MB of free hard disk space (4 GB of RAM is recommended, especially for larger models).
Code language	Information not available.
Original application	The first major application of WEAP was in the Aral Sea region in 1989.
Public/proprietary and cost	The source code is proprietary. License fees vary from free to $3000 for two years use, based on criteria such as non-profit/for-profit status, academic status, developing vs. high-income country.
Physically or empirically based	The model is physically based.
Mathematical methods used	WEAP calculates a water and pollution mass balance for every node and link in the system on a monthly time step. Water is dispatched to meet instream and consumptive requirements, subject to demand priorities, supply preferences, mass balance and other constraints.
Input data requirements	The user enters data under the following categories: Key Assumptions, Demand Sites, Hydrology, Supply and Resources, Environment, and Other Assumptions.
Outputs	Model outputs include demand, supply, costs, and environmental loadings. It is possible to export schematics and results to Google Earth.
Pre-processing and post-processing tools	The model is integrated with a Graphical User Interface (GUI), which allows for pre- and post-processing.
Representation of uncertainty	The basic PEST tool (pest.exe) is included in the WEAP installation. PEST (Parameter ESTimation) is a free software package for Model-Independent Parameter Estimation and Uncertainty Analysis.
Prevalence	WEAP has been applied in water assessments in dozens of countries. DWR is using a customized version of WEAP for the California Water Plan Update 2018.
Ease of use for public entities	There are no barriers to the widespread use of the model. Training and model support are readily available. The source code is proprietary, which prevents modification of the model for specific applications.
Ease of obtaining information and availability of technical support	There is an active on-line user forum. Training course are offered periodically.
Source code availability	The source code is proprietary.
Status of model development	The model continues to undergo development and new versions are regularly released. Recent updates to WEAP have focused on model usability, demand calculations, and linking the model to LEAP (SEI's software for energy planning). SEI-US will customize the WEAP software to accommodate the particular needs of a given project.
Challenges in integration	The model is proprietary, which is a challenge or barrier to integration with other models. However, the ability of WEAP to call DLL functions is very powerful, as it allows the user to add new functions or even complete models to WEAP.