As the summer draws to a close in California, all hopes are on El Niño rains providing much-needed relief for this drought-stricken state. Yet even if rain falls where it’s most needed – in the northern and central parts of the state – the water crisis will be far from over. With demand that exceeds the sustainable supply, and climate change leading to hotter and drier weather conditions, water scarcity is almost certainly “the new normal”, as California’s Governor Jerry Brown has put it.

SEI has worked with water resources managers in California for many years, and as state and local officials seek long-term solutions to the water crisis, they are relying on SEI’s Water Evaluation and Planning (WEAP ) tool and on the expertise of SEI scientists based in Davis, in the heart of the Central Valley.

“The main lesson from these four years of drought is that we need a more sustainable and long-term approach to water use – and one in which decisions are made involving all key water stakeholders in the state,” says Vishal Mehta, a senior scientist at SEI-US. Using WEAP and a complementary participatory approach developed by SEI, “robust decision support” (RDS), water agencies in California are exploring their options for a drier future.

Water has long been a contentious issue in the state, with supplies strained by a growing population of 39 million and 50 billion USD, water-intensive agriculture sector . Declining river flows also threaten biodiversity and hydropower. Policy-makers and planners thus face tough choices. Accurate information and good tools to model supply and demand under different scenarios are crucial.

Innovative tools and practices promote innovative solutions

This is where WEAP comes in. First developed by SEI in 1988, and constantly expanded and improved since, WEAP takes an integrated approach to water resources planning, looking at supply and demand together to identify key factors that affect water system performance and to model different management strategies.

“WEAP gives us a holistic view,” says SEI-US Water Group Director David Purkey. “It allows us, in collaboration with our water management partners in California, to look at how climate change might affect snowmelt in the Sierras, the patterns of runoff in rivers, what is needed for the health of ecosystems under a warmer future, and how this affects different water users such as farmers or urban residents. Then we can test different policy options, and find the solutions that are most robust in a wide range of future scenarios.”

California’s Manager for Statewide Water Planning, Kamyar Guivetchi, who oversees the development of California’s Water Plan, has used WEAP since 2009. It is a useful tool, he says, “because it allows us to most expeditiously evaluate a broad range of scenarios. This enables us to take an integrated systemic approach to water management.” WEAP’s graphic interface and the ability to view model results without buying the software are also valuable, he adds, as those results are shared with stakeholders across the state.

This year, WEAP has been used to model and evaluate water management options in all 10 of California’s key watersheds. The tool has also been adopted by the California State Water Resources Control Board, responsible for decisions that relate to water quality and environmental health. It is being deployed to assess water flows into the Bay Delta from the Sacramento Valley watershed.

Working with the State Board represents an important shift in SEI engagement with the California water management community, as the board has the legal authority to modify the state’s water rights system to ensure that ecosystems are protected during the current and future California droughts.

Pioneering groundwater management analysis

SEI has also been working in Yolo County to use WEAP to analyse groundwater and surface water use together. This is pioneering work, as California is one of the few states without groundwater regulation, which means that pumping is not controlled or monitored – despite the huge pressure put on groundwater reserves by the drought.

Last year, the state approved the Sustainable Groundwater Management Act, which requires local and regional authorities to adopt groundwater management plans by 2022. SEI’s work in Yolo County could therefore provide a useful test case for other California water districts as they seek to curb groundwater overuse.

With SEI’s help, the Yolo County Flood Control and Water Conservation District has been assessing different options, from recharging the groundwater basin using canals that channel winter stormwater, to land use changes based on annual water availability.

Tim O’Halloran, general manager of the district, praises SEI experts for “forcing us to think about the broader framework for organizing water resources, from how to quantify groundwater, to pumping costs and locations, to the range of strategies we might use.”

An emphasis on stakeholder engagement

A key reason why SEI and WEAP modelling have made a real impact in California, Purkey says, is the way the tool has been applied, with an emphasis on working closely with stakeholders.

“Models by themselves don’t change discourse,” Purkey says. “The key is the way we use WEAP to encourage different ways of thinking about models and different assumptions.”

In all of its work in California, SEI is sharing WEAP model outputs, in accessible visual formats, with key local stakeholders, enabling them to develop a common understanding of water resources in their region and the different trade-offs of strategies to manage them. This has helped to bring together groups that have often been in conflict, such as farmers and environmentalists, and helped them to engage constructively with each other for the first time.

“Collaboration and co-learning are key,” says Purkey. “If we want to adapt successfully to this ‘new normal’, we need both stakeholders and scientists at the table in order to properly understand the challenges we face. Only then can we make the best possible decisions for managing our water resources well into the future.”

Learn more about WEAP »

Learn more about SEI’s use of visualizations for decision support »