Shared from the 4/23/2017 Houston Chronicle eEdition

WEATHER

DOES CLIMATE CHANGE MEAN MORE BIG STORMS?

Officials in Houston and Harris County aren’t sure, but some scientists are

Picture

Floodwaters inundate the Wimbledon Champions Park subdivision on April 19, 2016.

Brett Coomer / Houston Chronicle

Picture
Michael Ciaglo / Houston Chronicle file

Good Samaritans paddle through Arbor Court Apartments in the Greenspoint area looking to help people evacuate during the Tax Day flood last year. Fears remain for many residents that they may have to endure more such disasters.

Picture

Katharine Hayhoe says climate change has played a role in recent floods.

Picture

As a string of thunderstorms rolled through Harris County last week, local flood control officials were monitoring creeks and bayous, all of which stayed safely in their banks.

That’s in sharp contrast to last spring, when back-to-back floods dumped biblical amounts of rain, prompting many Houston residents to wonder if heavy downpours were the new normal thanks to climate change.

Local leaders aren’t sure. They are still searching for definitive proof, bristling at the notion that current climate change projections should alter flood control efforts.

“We don’t knee-jerk react to having a very wet year,” said Russ Poppe, the new executive director of the Harris County Flood Control District, about 2016.

Instead, the district is seeking more data about rainfall frequency as it considers the idea that climate change might be increasing heavy downpours. County officials have contributed funding to a federal study to update that information for Texas, a task not expected to be complete until mid-2018.

Many scientists say that concerns about climate change are justified, pointing to studies that suggest Houston and other coastal cities can expect more frequent flooding in the not-so-distant future. Some believe that climate change is already influencing the extreme weather here.

“The No. 1 question people ask when there’s an extreme event is, ‘Is this climate change or is this natural?’ ” said Katharine Hayhoe, the acclaimed climate scientist from Texas Tech University. “The answer is that human-induced climate change has irrevocably altered the background conditions of our atmosphere. And so everything that happens now has some component of climate change. The question is now, how much?”

Mayor Sylvester Turner appointed Stephen Costello as Houston’s flood czar last year in the aftermath of the Tax Day flood, seeking someone who would “revise and update policies and ordinances to mitigate the risks of potential events.”

Ask Costello today if climate change is behind not just Tax Day but also the four storms in the past two years that should come around once every century, he says: “I haven’t come to that conclusion just yet.”

Costello and Poppe, two of the top flood control officials in the Houston area, caution that weather extremes have been a regular, and expected, part of the region’s climate.

Poppe points to cycles: There are droughts, like the one in 2011, which dried out much of the state, including the Houston region. It killed tens of millions of trees and fanned devastating wildfires that burned dozens of homes to the ground.

Then there are years like the past two, or 2001, with Tropical Storm Allison. To say that climate change is behind these swings would be premature, Poppe and Costello say.

And the district is already constrained by its budget, Poppe said. For example, the Brays Bayou project, one of the largest flood control efforts ever conducted in the region, in a neighborhood notorious for floods, won’t even be able to protect all of the areas along the channel from the current 100-year storm estimate, meaning that even routine storms could flood homes despite improvements — more protection would necessitate more money.

Costello also said rainfall projections, climate change or not, are an inexact science, limited by the small pot of data used. It’s difficult to accurately predict the next day’s weather, he said, let alone how the whole climate could be shifting.

In the aftermath of Allison, the city and county undertook a concerted, multimillion-dollar effort to better understand how storms impact the region. It showed that the estimates of how much it would rain during a 100-year storm were underestimated by several inches in some parts of the county.

Some climate scientists say not only is more flooding in Houston’s future, those storms will be more intense.

It’s simple physics. As the Earth warms, the atmosphere is capable of holding much more moisture.

Already, torrential downpours in Houston are happening much more frequently than they did in the early 20th century.

An analysis by John Nielsen-Gammon, the state climatologist appointed by George W. Bush in 2000, shows that downpours that struck every two years back then now come every year on average. Deluges that used to drop each 100, 500 or 1,000 years should fall more frequently as well.

“We’ve confirmed that there’s an overall increase in extreme rainfall in Texas over the past century,” Nielsen-Gammon told the Chronicle last May after the Tax Day flood. “Specifically for Houston, the increase has been particularly large.”

Hayhoe said it’s clear that climate change has played a role in Houston’s recent floods. At the same time, she acknowledged the city’s natural propensity to flood.

“The analogy I would use is this: Someone has a heart attack. They go to their doctor, and say, ‘Was the cause genetics or lifestyle?’ And the doctor says, well, it was probably a little bit of both. Right? Because unless you come from a family where every single person has had a heart attack, or unless you lived a lifestyle that was obviously, completely unhealthy, for most of us, our heart risk is a combination of genetics and lifestyle. So just because our genetics might predispose us to a heart attack, it doesn’t mean that our lifestyle doesn’t make a difference. It does. Houston has always been at risk from ‘genetic’ heavy rainfall and hurricanes, but climate change is increasing the risk because of the lifestyle choices we make, such as how we get our energy or how much impervious surfaces and pavement we put down.”

B B B

While scientists overwhelming agree that climate change is influencing extreme weather around the globe, they have been reluctant to say how much it’s driving those events.

That appears to be changing, too.

When downpours caused deadly flash flooding last August in Louisiana, a group of scientists was able to determine that climate change increased the odds of that event by 40 percent and increased the intensity of the storm by 10 percent.

The team, which included scientists from the National Oceanic and Atmospheric Administration, performed the assessment by analyzing rainfall observations and using two of the federal agency’s high-resolution climate models.

“You have to make sure you have sufficient data and carefully review that data to conduct your analysis,” said Heidi Cullen, the chief scientist at Climate Central who helped conduct the assessment of the Louisiana floods. “But in the case of Louisiana, we had enough to say that climate change increased the intensity.

“I’m not sure why the flood control district in Houston would need to wait on any data to see how climate change has influenced extreme weather there,” she said. “It seems like there’s enough information at this point.”

B B B

Jazurnique Okray doesn’t need to be convinced that flooding is increasing in Houston.

A year ago, as a resident of the Arbor Court apartment complex in Greenspoint, she watched her television, family photos and furniture float out the front door during the Tax Day flood.

The fear remains.

“I feel like it’s kind of traumatizing,” Okray said. “Every time it rains, I’m always looking outside. Is this water going to come in here?”

Despite the reluctance of local officials to acknowledge climate change is behind Houston’s worsening weather, they still point to several steps being taken in the wake of recent flooding.

In addition to appointing Costello, the city has worked with the flood control district to channel $46 million in state funds to Brays Bayou — never before done.

He said a “stormwater action team” in the public works department, with $10 million in funding, is identifying repeat flood areas and seeing if it can invest in new infrastructure there — ditches, culverts, inlets or other measures.

Costello said the city will re-examine its criteria for developers to make sure they are doing enough to offset their potential impact on floodwaters, which happens when they pave over flood-absorbent ground.

“I think as a result of the last two years of flooding, the public does want to take a new look at our criteria,” he said.

The flood control district also has hired a consultant to re-examine its detention requirements — how much water developers must hold back to offset the impact of pavement — to see whether they are effective.

Costello said the city also will look at the results of the federal analysis, which the district helped fund with $200,000, and see whether or not that means more changes should be in the works. The study is being conducted by NOAA, which has already provided precipitation frequency estimates for most of the country. The agency’s estimates are based on a stationary climate, something it concedes there are questions about. It is reviewing its methodology to determine whether future estimates should be based on a climate in flux.

B B B

Houston has won national accolades for its commitment to reducing greenhouse gases and for embracing renewable energy, efforts jump-started under former Mayor Annise Parker.

But environmentalists say local leaders should come up with a plan to adapt to the changing climate.

“I think it’s time the flood control district acknowledge the problem,” said Luke Metzger, director of Environment Texas. “It’s reckless and irresponsible not to do so.”

Talking about climate change in Texas has never been easy. Many state leaders are skeptical, while others simply deny that humans are causing the Earth to warm.

That’s in stark contrast to other cities and states, which factor climate change into planning efforts. Louisiana’s $50 billion coastal master plan, for example, cites climate change as one of the primary culprits behind both rising sea levels and increased flooding. Similarly, NASA, the Department of Defense and the Army Corps of Engineers have studied how climate change affects operations.

In 2015, Austin adopted a plan that identifies threats due to climate change and how the city is tackling those challenges or plans to do so in the future. It mentions, for example, how more intense heat waves might prompt the city to plant trees better adapted to a hotter climate.

Until there’s a seismic political shift on climate change in Texas, many believe businesses, industries and nonprofits will drive any shift in practices or preparation.

Already, some local architecture firms, backed by the Houston-Galveston Area Council, have adopted “low-impact” design strategies to help with flood control. These include structures like “green roofs,” increasing vegetative cover and installing rain barrels.

Those projects should augment current flood control efforts, which will be tested not only by climate change but also by an increasing population.

“I think the one thing we all agree on is that more and more people are going to move to Houston in coming years,” said Lisa Gonzalez, president of the Houston Advanced Research Center. “That alone is going to trigger a paradigm shift on flood control.” kim.mcguire@chron.com mihir.zaveri@chronc.om

›› See flooding estimates and more rain-related information at HoustonChronicle.com/floods

See this article in the e-Edition Here
Edit Privacy