Experts say expect more floods, more often


Expect more heavy rain, more often, and get ready for even worse from named storms and hurricanes. That’s what experts warn, and they say our infrastructure needs to change to keep up. 

Over 25 years teaching weather at the University of Hawaii, Steven Businger, UH Atmospheric Sciences Department profession and chair, has seen big storms and floods come and go. He says what used to be rare is becoming more frequent — and all the engineering to withstand it needs to be rethought. 

“For those people who were flooded, this past weekend, I feel sorry for them but they can expect that to happen again in the next five years,” Businger said. “There will be another flood. I would say that’s the return period for a storm like this.

It used to be every 10 years, he says.

“We don’t generally design things for a 100 year return period but I think we should. We should start doing that because these floods, unusual floods are becoming more common,” he explains. Why? “The sea surface temperature is warming with climate change, and warmer sea surface leads to a larger amount of water vapor. It pushes water vapor into the air and so the result is storms that produce heavier rain, and that’s been shown all over the world that’s happening.”

“But a much bigger problem is a hurricane,” Businger adds, “because then you’re going to have the flash floods plus the high winds plus the storm surge. If we don’t harden our infrastructure for the possibility of having a hurricane hit Honolulu, then I think we’re doing our society a disservice.”

Honolulu’s Office of Climate Change, Sustainability, and Resiliency is charged with studying how best to do that in a race against time. 

KHON2 asked its director Josh Stanbro, what is changing that we can’t sustain these heavy rains, let alone a named storm or a hurricane?

“There are two reasons and they’re tied together,” Stanbro said. “As the sea level rises it makes it harder for the rains we do get to fall out to the ocean. So what’s happening is it’s getting harder and harder for these big rain events to actually drain as the sea level comes up. There’s no place for it to go. The other thing is that these rain events are getting bigger and bigger. So we’re seeing less rain over time, but when it does come it comes in this big downpours. We’ll have to be taking a look at that and seeing what are the things accepted over time that really don’t work going into the future?”

That’s everything from how roads, bridges and drains are planned, whether homes near shores or culverts will need setbacks or stilts, and tackling the massive task of keeping storm water from overwhelming sewage lines. Sewer resiliency was one win in the East Oahu storm. 

“We didn’t see any sewer breaks, and so you get this big rain, and for the system to hold up it shows that the investments we’re doing now are starting to pay off,” Stanbro said. “There’s another sewer program over in Kaneohe. That’s actually designed to hold the rain water in the big events in a tunnel if it can, to release it in little bits later. So these are the kind of things we really have to start designing in now.”

The state Department of Transportation has been taking a look at redesigning coastal highways prone to flooding. That hadn’t been a problem with Kalanianaole Highway though, and the state says the culverts near the highway were clear ahead of the storm. 

“The drains and everything were clear prior to the storm event, but sometimes when you do have a rain event of this magnitude, all the water can bring down vegetation or debris from the hillsides or the canal down to the drains and closer to the highway and things which is what happened in this case,” said D.O.T. spokesperson Tim Sakahara. “Historically Kalanianaole Highway has fared pretty well in storm events and rainfall events.”

KHON2 asked, is Kalanianaole Highway an area that the experts will go back and see why, what happened there, and what can be avoided in the future? 

“Possibly, anytime you have an event like this there are after action events and meetings that take place to determine if anything can or should be changed,” 

Both the city and state tell us it was just too much water, too fast for the existing drainage infrastructure. We’ll follow up on any big changes that can be made there, and how soon.

Copyright 2019 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.