Richard Vogel/AP

L.A. and other desert cities exist by importing vast quantities of water, but Peter and Hadley Arnold of the Arid Lands Institute have a different idea.

In a sense, municipal water systems are infuriatingly inefficient. They maintain an extensive network of pipes and pumps to bring fresh water into the city—along with a sewer system that flushes rainwater down the drain.

One egregious example is Los Angeles, which imports the large majority of its water, at great cost, from hundreds of miles away in the Colorado River Basin, the eastern Sierras, and the Sacramento-San Joaquin Delta. Yet according to Southern California's Metropolitan Water District, 82 percent of the city's water needs could be met locally, through recycling, conservation, and the strategic harvesting of rainwater.

This is the big organizing concept behind the current work of the Arid Lands Institute, a tiny design think tank run by Peter and Hadley Arnold at Woodbury University in L.A. Both trained as architects, they are now spending their time not on designing futuristic buildings, but on creating a giant model of the L.A. region—a "hydrologic zoning overlay," says Hadley—that lets city staff, developers, and designers alike see beneath the surface and design appropriately to capture this precious resource.

The project is called Divining LA: Drylands City Design for the Next 100 Years, and a central part of it is the development of a software application called Hazel (named after the traditional divining rod) to make it easy to comprehend and navigate the region's hydrologic information. The model shows such things as areas of contaminated land, where water would be better captured in rooftop cisterns; and where it make sense to install permeable paving and allow rain to replenish groundwater supplies.

"Cities are currently designed to rid us of rainwater as fast as we can, to mitigate flood concerns," Peter Arnold says. "Instead, cities could be more like sponges." If this approach gains ground in L.A., it could be a potent model for parched regions worldwide.

The Arnolds became inspired to become waterbearers in the environmental movement in the mid-1990s. After architecture school, they started their own practice, while pursuing other projects of interest on the side. Peter, who also does large-format landscape photography, received a couple of grants to shoot panoramic images of water infrastructure as a form of environmental criticism.

"I could see how all the sources of water we depended on were these highly contrived and engineered things, and how water was shaping our own settlement patterns and urbanism," he says. "People used to organize ourselves around what water was available, but then we moved to the 'Let's deliver water' approach, which flattens out topography and culture."

A geospatial model showing where stormwater can be captured in the San Fernando Valley (Arid Lands Institute)

Leveraging his undergraduate degree in environmental design and physics, Peter began to work with GIS software to create models that combine topography, soil types, groundwater resources, contamination sites, and development at a very granular level. The Arnolds support their work with federal grants from HUD and the EPA, as well as corporate and individual donors. (Divining LA was in the running for $100,000 from LA2050's My LA2050 Grants Challenge, but didn't win; this year's 10 winners were just announced.)

As climate change and California's severe drought make water an urgent concern, the rest of the world may be finally catching up to the Arnolds. Still, their modest office at Woodbury, which they share with a couple of architecture faculty members, consists of 16 square feet of desk space that is piled with papers. "It looks very banal, like a Congressional staffer's desk," jokes Peter. Adds Hadley, "We're lean, but not mean."

Peter and Hadley Arnold (Arid Lands Institute)

While they aren't surrounded by glamorous renderings, the Arnolds are convinced that their work will eventually prompt them. "The visibility of water systems will play a huge part in bringing water back to the public consciousness," Hadley says. "That's the fun part." She expects design to move toward integrated systems, such as roofs that include cisterns, and wall packages that store water while providing a thermal advantage.

"Right now we're doing the pre-design work, making the modeling of hydrologic flow available and intelligible to the design profession," Hadley says. "We see brave, poetic, and effective acts of design coming out of it."

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