Frequently Asked Questions

General Information/Getting Started

What is WEAP?

WEAP is a software tool for water supply and demand planning. It is particularly valuable as a tool for scenario analysis. Scenarios may include, for example, climate change, land use changes, population growth, changes in water use efficiency or demand management, changes in land uses and irrigation, and infrastructure. WEAP’s automatic catchment delineation feature makes building new models easy by building catchments based on digital elevation maps, and land use and climate data, all of which are included with WEAP as global datasets. WEAP includes built-in models for: Rainfall runoff and infiltration, evapotranspiration, crop requirements and yields, surface water/groundwater interaction, reservoir operations and hydropower generation, and instream water quality. Demand sites can include customized data on water use, loss and reuse, demand management, water quality, and cost. Data entered can be adjusted for monthly variation. Water supply sources are similarly customizable. Both supply and demand nodes can be assigned priority ranks. The timestep for WEAP models is flexible, from daily to weekly to monthly.

I’m new to WEAP. What’s the best way to learn the software?

Resources to help you get started:

  1. Tutorial exercises: www.weap21.org/tutorial

  2. YouTube channel with videos grouped by language and topic: https://www.youtube.com/c/WEAP-System

  3. Online, interactive, instructor-led introductory training www.weap21.org/training

  4. Online help and user guide: https://www.weap21.org/userguide/

  5. Review WEAP publications to see how WEAP has been used by others: www.weap21.org/publications You can search by location and keyword.

  6. User support forum for technical questions: www.weap21.org/forum

  7. See if your university offers a course that teaches WEAP: www.weap21.org/courses

How do I cite WEAP?

To cite the software itself:

Jack Sieber, Water Evaluation and Adaptation Planning (WEAP), Software version: <version number, e.g., 2026.10.2>, Stockholm Environment Institute, Somerville, MA, USA, https://www.weap21.org

To cite an early peer-reviewed article describing WEAP:

David Yates, Jack Sieber, David R. Purkey and Annette Huber-Lee, "WEAP21--A Demand-, Priority-, and Preference-Driven Water Planning Model: Part 1, Model Characteristics," Water International, Vol. 30, No. 4, pp. 487-500, doi:10.1080/02508060508691893, December 2005.

What operating systems support WEAP?

WEAP runs on Windows and can also be operated on Mac or Linux with emulation software, such as VMWare Fusion or Parallels Desktop.

Does WEAP require a lot of data?

WEAP is as simple or as complicated as you want to make it. WEAP is flexible in its data inputs. The model can work with simplified assumptions in areas you lack detailed data by using default values and estimates, and can also handle detailed data inputs when you have better available data and need more details. WEAP has built-in global databases of land use, elevation, and climate to automate the process of catchment and river delineation.

Do I need a license to run WEAP?

The evaluation version of the WEAP software is available for free download from our website. Without a license, you can complete the tutorial exercises and explore all capabilities in WEAP except saving changes to datasets larger than 6 nodes and 3 rivers or using the Application Programming Interface (API). For more information on licensing, please fill out a WEAP profile and see www.weap21.org/licensing.

Why can’t I save changes to my profile?

Check for the following:

  • All required fields (denoted in red text) are entered.

  • If you aren’t trying to change your password, the “Change Password” field should be blank. (Your web browser might auto-fill it, depending on your settings.)

How do I change my PC to United States date and number formatting conventions while using WEAP?

  1. Open Settings (type settings or Press the Windows Key + I)

  2. Click on Time & language in the left sidebar.

  3. Select Language & region.

  4. Scroll down and click on Regional format to expand it, then select United States.

Model Capabilities

Is WEAP suitable for large-scale projects?

WEAP is flexible and can be used for both small and large-scale water resource planning projects. Examples of large projects that have used WEAP include the Nile Basin, the Colorado Basin, and the country of Bolivia.

Can WEAP export results for external reporting?

Yes, results can be exported in various formats (Excel, Word, PowerPoint, Google Earth, HTML), suitable for external reporting, presentations, and analysis.

Can WEAP model groundwater interactions?

Yes, WEAP can model groundwater dynamics, including recharge, extraction, and interaction with surface water, using either built-in models or by linking to MODFLOW models.

Can WEAP simulate agricultural water demand?

Yes, WEAP supports agricultural demand modeling, including crop requirements, irrigation efficiency, and crop yields.

Can WEAP model inter-basin water transfers?

Inter-basin transfers are modeled as transmission links. Adjusting inflow and outflow nodes can replicate transfers.

Can WEAP handle multi-basin models?

Yes.

Can WEAP model reservoir evaporation?

WEAP allows users to set evaporation parameters based on climate data, which can be customized for each reservoir.

Can WEAP simulate flood control measures?

Yes, flood control can be modeled through reservoir rules, setting target levels and overflow triggers.

How easy is it to customize expressions and program relationships with WEAP?

WEAP has a flexible expression language (similar to Excel) that can be used to build complex models and relationships. Users can define their own variables. An Application Programming Interface (API) can be used to automate WEAP and its connection to other software.

Model Setup and Calibration

What is the fastest/easiest way to set up a model?

In Catchment Delineation mode, WEAP automates creation of basins and rivers, and downloads climate and land use data according to pour points identified by the user. The user can then add demand and supply sites, as well as relevant infrastructure. Use existing flow data (from a gauge or another model) to help calibrate the catchments. 

What is the process for adding shapefiles to a WEAP model?

Shapefiles can be added via the “GIS Layers” feature, enhancing spatial data representation in the model. All background layers must use the same geographic projection.  If you add a layer and it does not appear on the Schematic, it may be because it does not use the same projection as the existing background layers.  WEAP's preloaded global layers use the WGS84 projection (WGS84 files are sometimes referred to as "unprojected," because they are based directly on latitude and longitude.)  If you want to add layers that use a projection different from WGS84, here is what you should do.  (Note: you must do this BEFORE you add any WEAP objects, such as rivers or demand sites, because when you add them they will use the projection in effect, and will disappear when you change to using a different projection.)  Add one of your layers.  Remove all layers (such as the preloaded layers) that are in a different projection.  Go to Set Area Boundaries and set the boundary using your new layer.  If your layer is visible in the Schematic then you have done it correctly.

How do I change the label and node size on the schematic?

In the Schematic View, go to the menu Schematic --> Set WEAP Node Size or Set WEAP Label Size to change the size of all objects and labels.
If large arrows persist and your modeled area allows, try setting the area boundary to be much smaller. (Right click on the schematic --> Set Area Boundaries.) Larger area boundaries will have larger arrows.

What are some tips for setting up a demand node?

Demand nodes require data on population, consumption, and seasonal variation. Start with averages and adjust as needed.

How do I calibrate a WEAP model using observed data?

Calibration involves adjusting parameters to match observed data. Comparing simulated and observed levels helps refine the model. WEAP calculates calibration statistics, such as Nash-Sutcliffe Efficiency (NSE), Kling-Gupta Efficiency (KGE), Bias, root mean square error (RMSE) and r2.

Can you tell me more about model calibration?

Calibration is challenging and time-consuming for any hydrologic model.
Here are some basic tips:

  • You need to calibrate your soil moisture parameters to match your modeled and observed streamflows. Start with the gauge location with the fewest upstream human diversions and operations. 

  • Study your modeled versus observed streamflow results. Is your annual observed streamflow more or less than observed? What about the average monthly flows? What about for large precipitation storm event peak flows or base flows during dry seasons? Could there be surface-groundwater interactions that need to be represented? 

  • Also, study your results for soil moisture (z1 and z2). Make sure that the soil moisture levels follow a believable trend and are not consistently at 0% or 100%. If your soil moisture pattern is irregular see the associated advice in the Tutorial. 

  • If your model is producing simulated flow less than the observed flow, some parameters to adjust could be to decrease Kc, decrease runoff resistance factor, decrease soil water capacity, increase preferred flow direction, and increase root zone conductivity. The Catchment Calibration Tutorial chapter explains further. You can experiment to see which parameters are most sensitive and start by adjusting the most sensitive one first to achieve the best match to observed flows, then move on to the next most sensitive. You may have to run through this process several times. 

For calibration questions, the best resources are our catchment calibration chapter in the WEAP Tutorial. Additionally, we have video lessons available on calibration on YouTube: https://www.youtube.com/watch?v=Notx1vfeRCk.

How can I integrate climate data and projections into WEAP?

Climate data can be automatically downloaded (both historical and CMIP projections, using automatic catchment delineation) or manually imported for simulations. Users can explore future scenarios by adjusting climate variables.

Integration with Other Tools

Does WEAP integrate with GIS software?

WEAP supports GIS integration for spatial data visualization, making it easier to analyze geographic influences.

What are the options for importing external data into WEAP?

Users can import data in CSV format for integration into model parameters and scenarios.

Can I link WEAP with other models?

Yes, WEAP can be linked with SWAT, QUAL2K, MODFLOW, and other models to enhance watershed and hydrological analysis. WEAP can also be linked to LEAP when your project integrates energy sector analysis.

Is it possible to connect WEAP to SCADA systems?

WEAP can connect with SCADA systems indirectly through data exports and imports, and automation (API).

Does WEAP integrate with machine learning tools?

Yes, WEAP can be integrated with machine learning tools through custom scripting. Users often connect WEAP with tools like R or Python for advanced data analytics.

Technical Support

How do I update WEAP?

WEAP will check on startup for new versions and offer to download and install. You can also check for new versions via the WEAP menu: go to Help, Check for New Version. Updates are also available on the WEAP website, and installation instructions are provided. The latest version of WEAP is always available at www.weap21.org/download

Will my models and data be preserved when I install the latest version of WEAP or enter a new registration code?

Yes. Upgrading WEAP and/or entering a new license code to replace an expired one does not affect access to your existing models. When your registration code expires, you can still open and view your models, but you cannot save any changes to them.

How do I change the location of the WEAP Areas folder?

You can change folder locations in WEAP under General, Folder Locations.

How do I find solutions to common errors in WEAP?

The user guide and forum cover many common issues. Users are encouraged to search or post for specific help. www.weap21.org/Forum

What can I do to make WEAP run faster?

You can turn off any unneeded result variables: on the menu in the Data View, go to Edit, Result Variable, Select Results to Save. Turn off unneeded scenarios: go to Area, Manage Scenarios. If you have a fast disk (SSD or NVMe), you should move your working folder to it. Go to General, Folder Locations to move it.

What new features are in the latest WEAP version?

Updates in the latest version of WEAP can be reviewed at www.weap21.org/whatsnew

How do I back up and save versions of my WEAP model?

WEAP has three modes for saving models as they progress: saving versions, saving the model, and creating a backup file. Regularly saving versions or your model are recommended for large projects. Every time you save your model in WEAP, WEAP automatically creates a version of the model. You can also save a version with a comment: Area, Save Version. Go to the menu Area, Revert to Version to browse previously saved versions to restore if necessary. Creating a backup file, by going to the menu Area, Manage Areas, and select “Backup” is the best way to create a file to share with colleagues or for future reference. This backup can itself contain one or more versions.

Career Opportunities

Are there job openings or internships for WEAP-trained individuals?

When there are job openings at SEI requiring experience with WEAP, they are posted on the WEAP forum and SEI website, particularly for roles in water resource management. Other organizations’ WEAP-related job openings (when we’re made aware of them) are shared on our LinkedIn group: https://www.linkedin.com/groups/13182407/

How can I connect with other WEAP professionals?

The WEAP forum is a good way to connect with other users. Go to https://www.weap21.org/membership to see the list of other users.

To share and discuss WEAP-related projects, join our LinkedIn group: https://www.linkedin.com/groups/13182407/

Does SEI offer WEAP certifications?

Certificates of completion are offered to participants at the conclusion of SEI-sponsored WEAP trainings.

What career paths use WEAP extensively?

WEAP is used in environmental consulting, government agencies, academia, and NGOs focused on water resource planning.

Still have a question? Ask in the WEAP Forum