When a drought turns into an urban water crisis, a city’s first step is often to limit lawn watering and launch a campaign to encourage everyone to conserve. It might raise water-use rates or offer incentives for installing low-flow devices.

While demand management techniques like these have had in reducing water use, our new research suggests that they in the face of climate change.

We looked at three cities in the Colorado River Basin – Phoenix, Las Vegas and Denver – to understand what each could do to increase demand management amid water shortages and how far those methods could go as temperatures rise and the Colorado River’s flow weakens.

The results suggest the region needs to be thinking about bigger solutions.

Colorado River states’ immediate challenge

The Colorado River provides drinking water to nearly and irrigation for over of cropland. But it has experienced a in recent decades due in part to rising demand for water and a long-running .

To ensure that water is shared across boundaries, the seven states within the basin agreed to the in 1922, setting limits on water withdrawals from the river. Since then, the region has adopted additional rules, agreements and policies, collectively termed the “.” But despite this compact, which , the basin’s water supply is shrinking.

Research shows that the region is likely to experience that last longer due to climate change, putting the water supplies for farms, people and energy systems at risk.

As researchers who study the impact of climate change on water systems, we wanted to see if could help under these intensifying conditions.

Getting people involved can change attitudes

Many demand management policies are reactive and only go into effect when sources run low.

These reactive policies can be , but there is often a : Water consumption can actually increase afterward.

We integrated with a and demonstrated that there to the local water supply if communities encourage positive attitudes toward conservation.

The survey focused on how people think about water conservation and climate change, drawing on a large body of research that shows people who . Building off these ideas, we segmented the population into on water conservation and found that a large proportion of residents supported water conservation but weren’t actively participating in conservation programs within their communities.

We then used the computer model to explore how changing attitudes, and subsequent conservation behavior, could affect water supplies under climate change.

When participatory demand management works

Our research shows that individual actions, when implemented by a lot of people, can measurably improve water supplies’ reliability.

A great example of the benefits of long-term behavioral changes is Las Vegas.

Las Vegas is in many ways viewed as a city of excess; however, since 2002, the city has , even as the by more than 50%. It reached these savings through efforts to reduce seasonal irrigation, replace water-intensive landscaping and require new developments to be sustainable, along with the . Today, Las Vegas and returns it to Lake Mead.

Phoenix, another desert city, also . These programs focus on converting grass lawns to desert-friendly landscaping and encouraging owners to fix leaks and install smart meters and low-flow devices. These programs led to a , while the .

Demand management is not always enough

These cities have shown that demand management can work, but there are limits on how much these techniques can do as water supplies dry up.

When we added projections of future climate change to our model, we found that conditions could lead to so little water being available that these .

In other words, climate change may create situations where water supplies are still severely limited, even after people reduced their consumption by up to 25%.

For example, under a plausible, moderately high emissions scenario, Phoenix’s available surface water supply was forecast to drop below the historical average by 2060. Even when we simulated higher participation in conservation programs, there was no noticeable change in the water availability, suggesting that any savings from reducing demand were counteracted by losses from upstream flow reductions. Encouraging people to use less water is a start, but there is a limit to how much people can conserve.

We found similar results in Denver under a moderate emissions scenario and in Las Vegas under a moderately high emissions scenario, indicating that even moderate climate change could lead to extreme scarcity conditions that are not manageable through demand-side changes alone.

What else cities can do

In these cases, it may be necessary to find other creative water sources, such as water reuse, desalination or limiting consumption in other sectors, such as agriculture or energy, to maintain the municipal supply.

These solutions, however, take time and money to implement. . A recently built desalination plant in Carlsbad, California, cost US$1 billion – .

Other solutions, such as reducing agricultural water use, require significant buy-in from local farmers and could .

Reducing the would require significant investment in renewable energy technologies that have and nuclear energy.

While large-scale solutions like water reuse systems and desalination can be expensive, these costs might be necessary to maintain adequate water supply in the region, because simply encouraging people to use less won’t be enough.