As plans for the Central Arizona Project fell into place more than four decades ago, state officials made two decisions that reverberate even more loudly today than they did at the time.

Arizona agreed to let California take its water from the Colorado River first, even if it meant there might not be enough left to fill the CAP Canal, and the state elected to build a coal-fired power plant to run the canal's pumps.

"The two biggest decisions made to get us built put us in the most jeopardy," said David Modeer, the general manager of CAP, whose governing board and staff are working to reduce the risk of future water shortages and avoid the high costs of proposed air-pollution controls on the power plant.

The challenges facing the CAP are not unique. Over the past year, The Arizona Republic and azcentral.com examined the history and modern realities of the state's air, land and water management. In each, there was a common theme. Decisions made years ago, as the state grew and developed, have put those resources at risk today.

People in Phoenix and its suburbs breathe air that is polluted, sometimes to levels that bring daily health risks, because so many homes and businesses sit so close to freeways and congested highways.

Ponderosa pine forests, now home to many Arizonans and a cool refuge to many more, are on the verge of collapsing amid wildfires and insect attacks that thrive in the overgrown, uncontrolled stands of trees.

And water managers, who run systems that have survived historic droughts, now face a drier future with supplies based on shaky guarantees.

Plans are in the works to address all of these issues: air-quality plans for Maricopa and Pinal counties, a forest-restoration project in the high country, long-term approaches to augmenting water resources and securing more certain power supplies.

For those who manage the resources, and for the outside groups that seek better air, healthier forests and more water conservation, the recurring question is one of time. In systems that take decades to develop, can the decision-makers of today come together in time to avert the risks?

"If we're not feeling the pressure, if we're not feeling the discomfort or pain, we don't always deal with the future problem," said Sid Wilson, the CAP's former general manager who helped negotiate Arizona's stake in a Colorado River water-conservation plan. "It seems like we're always behind the curve. We need to be visionary again."

Health risks in air

In metropolitan Phoenix, a Republic analysis found in January 2012, more than 300,000 people live or work within one-third of a mile of a major freeway and more still live near congested arterial roads. That makes neighborhoods and businesses convenient, but it puts those people at greater risk of respiratory ailments.

A growing number of studies have shown that freeway exhaust is bad for health. A study by the University of California-Los Angeles found that people near freeways are exposed to 30 times the concentration of dangerous particles as people who live farther away. Another study by the University of Southern California found that children who live or attend school near a freeway show signs of weaker lung function.

And new research released in June by the State University of New York added to the evidence, finding higher rates of asthma among people who live near congested highways.

Yet air quality was not a prominent part of land-use planning as the Valley grew. Subdivisions, hospitals, office parks and as many as 30 schools were built along freeways and future freeway corridors. Although lawmakers in California have adopted rules restricting schools from lots near freeways, Arizona has not yet addressed the issue.

Meantime, Maricopa County has struggled to meet federal pollution standards, most notably for dust particles. The county has significantly reduced dust from construction sites, but farm fields, which are regulated under a separate state program, and vacant lots, whose owners often fail to comply with pollution rules, continue to push dust levels high.

Forests and fires

Over the past 10 years, wildfire has burned through one-quarter of Arizona's Ponderosa pine forests, the largest contiguous stand of the majestic tree on this continent. In all, a decade of fire has damaged an area the size of Connecticut.

Forest experts say the cause of the destruction is clear: There are too many trees. The forests grew thick and unhealthy amid a series of well-meaning land-management decisions: unregulated grazing, almost total fire suppression and a sudden halt to logging that allowed small-growth trees to multiply.

Wally Covington, director of Northern Arizona University's Ecological Restoration Institute, said the choices made decades ago seemed correct to most people in charge of the land.

"At that time, our understanding was fires were the enemy of the forest," Covington said, "just as wolves and mountain lions were enemy of the deer herds. No one really realized at the time how important they were as self-regulatory mechanisms for the ecosystem."

As more people moved into the forests, allowing fires to burn freely was not an option most state officials would consider. And federal forest managers worked under a policy that new fires needed to be put out as quickly as possible.

The damage done by the mega-fires of the last decade will linger in the forests for centuries no matter what land managers decide now, but a new project aims to reduce the risk of new fires. Under the Four Forest Restoration Initiative, more than 1 million acres of trees in four national forests will be thinned over the next 20 years, removing fuel for big fires.

Once thinning has been allowed to work, land managers say they will try to reintroduce fire as a natural regulator of forest growth, creating a sustainable landscape for future generations.

Water amid drought

No one would have believed that Arizona, one of the driest states in the arid West, would find itself with too much water, but that was the case in the years after the Central Arizona Project Canal was finished.

By deciding to divert more than half the state's Colorado River allocation through the canal, Arizona leaders created a water supply that Phoenix and Tucson had to grow into. Now, 40 years after construction began and nearly 20 after work wrapped up, water managers face new choices to maintain the certainty of the supply.

The CAP must deal with logistical concerns, including the prospect of water shortages in a severe drought and the loss of affordable electricity to power the canal's pumps. Longer-term choices loom as well, such as whether to continue using the water to maintain agriculture or make more available for future growth in cities.

"I think it shocks people that we really haven't had to make those choices," said Grady Gammage, a former CAP board member and a senior fellow at Arizona State University's Morrison Institute for Public Policy.

Leaving water for farms creates a buffer in times of drought. If Lake Mead had dropped low enough to trigger rationing in 2010 -- it came within about eight feet -- the first round of cutbacks would have affected agricultural users only.

There are risks further ahead based on yet other choices made more than 80 years ago, when the seven Colorado River states divided a water supply that has almost never been as plentiful as it was in those few unusually wet years.

So far, the states on the upper river -- Colorado, Wyoming, New Mexico and Utah -- have never used as much water as they believe they can, allowing the lower-river states to take what they need.

"If the upper basin began to grow like Phoenix did and use all their water," Gammage said, "then this whole thing is a problem."