Twenty-five years ago, SEI published the first version of its Water Evaluation And Planning (WEAP) system. Year after year, the software kept evolving and expanding, adding new features as SEI helped policy-makers and planners tackle ever more complex challenges.

Several U.S. government agencies, the United Nations, the World Bank, the Swedish International Development Cooperation Agency (Sida) and many others have funded key enhancements. In 2001–05, for example, for a major project for the U.S. Environmental Protection Agency, SEI added land use change and climate scenario modelling, which would become crucial for water resources, development and adaptation planning.

Today, WEAP is used by planners and researchers around the world. More than 40 WEAP-based studies were published last year alone – and the WEAP user forum has more than 18,000 members. Free one-year licenses to nonprofit, governmental or academic organizations based in developing countries have brought powerful analytical tools to users who could not otherwise afford them.

And through SEI research and capacity-building projects, WEAP capabilities continue to grow.

In August, developer Jack Sieber, deputy director of SEI’s U.S. Center, released a major new update of WEAP that brings together multiple enhancements made for recent SEI projects:

  • A new tool to model glacier shrinkage and growth and its impact on water systems, developed through SEI work in the Andes;
  • Capacity to analyse the impacts of changes in streamflow due to human activities (e.g. building a dam, deforestation) on ecosystems, through the integration of The Nature Conservancy’s Indicators of Hydrologic Alteration – the result of a collaboration in Colombia;
  • Modelling of the complex interactions between wetlands, river networks and floodplains, with improved understanding of flood risks – also a result of the Colombia project;
  • Much faster processing, up to 100 times faster for some models, making it easier to work with very large models with many scenarios – an improvement that greatly helped the California State Water Board in its use of WEAP for statewide water planning.

Those are the highlights; the full list includes more than upgrades and fixes; in addition, WEAP 2015 is compatible with the recently released Windows 10. The update is free to all licensed users.

“Managing water resources sustainably requires understanding a lot of complex interactions, weighing many different factors, and grappling with significant uncertainties,” says Sieber. “That is why WEAP is designed to be flexible, easy to expand and connect with other tools – so users can adapt it to their specific setting. We expect these new features to be useful to analysts all around the world, in both developed and developing countries.”

Marisa Escobar, a senior scientist at SEI-US, has led the glacier work in the Andes and a major project in Colombia – both funded by the U.S. Agency for International Development (USAID) – training local researchers and planners to use WEAP by building models with them.

“Water resources planning in these countries is a major challenge, because so much is changing at once: there’s economic growth, population growth, land use change, climate change, and also a growing awareness of environmental issues,” Escobar says. “Planners and policy-makers need to understand how all the pieces fit together, and how they may interact in an uncertain future.”

For example, Escobar notes, several South American countries depend on glacier-fed rivers for hydropower, agricultural water and urban water supply. “With climate change, glaciers are retreating rapidly, and we need to understand the implications and find robust solutions,” she says. “A surprising finding of our models is that the glaciers may not contribute as much to overall system flows as previously thought – but they are still very important for the landscape, and culturally as well.”

One of the reasons that SEI has been able to accomplish so much with WEAP, Escobar adds, is that modellers have worked closely with the user community to understand their needs, and sought funding and seized opportunities to make changes in respond to those needs.

“This has enabled us to produce models that we know will be useful and policy-relevant,” Escobar says. “Even better, all those new capabilities will now be available to all WEAP users, so they can examine glacier retreat, the impact of dams on wetlands and flood patterns, and other issues around the world.”

To learn more about WEAP and download the software, go to http://www.weap21.org.