WAVELAND, Miss. (AP) -- When Hurricane Katrina's punishing storm surge plowed ashore, it swamped seven of Coast Electric Power Association's substations, vital to powering thousands of Mississippi homes and businesses. The facilities have long since been repaired, but a decade after the storm they remain at the same elevation, and just as vulnerable to catastrophic hurricanes.
Such storms are a growing threat. An Associated Press analysis of industry data found that severe weather is the leading cause of major outages on the nation's power grid. The number of weather-related power outages has climbed over the last decade, with the greatest spikes in 2008 and 2011, according to the AP analysis and independent studies.
That leaves Coast Electric and other utilities across the country balancing customer costs with the need for improvements to counter the rising number of violent storms, floods and droughts threatening the U.S. power grid.
Katrina pummeled the Mississippi coast in August 2005, knocking out power to Coast Electric's entire coverage area.
Facing sweltering summer heat and $110 million in damage, the small nonprofit cooperative focused on restoring power quickly, said vice president of engineering Scott Brown. The substations that flooded were repaired to pre-storm conditions — at the time, it would have been impractical to raise them or move them elsewhere.
"We're only a few feet above sea level right here," Brown said during a recent visit to a substation in the coastal town of Waveland.
Coast Electric made some major improvements post-Katrina, like elevating a new substation 18 feet above sea level. But raising the old substations that flooded would cost Coast's 68,160 customers millions of dollars, Brown said.
Several thousand companies own and manage the equipment that makes up the U.S. power grid, from small municipal utilities and cooperatives like Coast Electric to large investor-owned companies like New York's Consolidated Edison.
When Hurricane Irene hit the Northeast in 2011, it marked the first time that more than 200,000 Con Ed customers lost power from a storm. Superstorm Sandy struck 14 months later, followed by a devastating Nor'easter, leaving 1.1 million customers in the dark.
"It was clear to us that weather patterns were changing fundamentally. Severe weather events were becoming more frequent and devastating," Allan Drury, a Con Ed spokesman, said in an email.
Con Ed is spending $1 billion to harden its system.
There are funds available from the Federal Emergency Management Agency to help utilities rebuild after catastrophes. The Mississippi cooperative received about $100 million in FEMA public assistance grants, but the money allowed it only to repair the flooded substations to pre-storm conditions.
FEMA offered more funds that could have been used to raise the flooded substations, but the co-op did not apply — cost effectiveness assessments and environmental considerations would have taken too much time, Brown said, and delayed getting the lights back on.
Once the work began, Coast Electric could not change the terms of the grant, Brown said. So the seven substations swamped by Katrina remain at the same elevation.
Utilities in other parts of the country face different challenges.
Last year, regulators in drought-stricken California ordered the state's investor-owned utilities to set priorities for inspecting and removing dead and sick trees near their power lines, warning that "climate change has facilitated and exacerbated numerous wildfires" that have damaged and threatened their facilities. Utilities could ask the California Public Utilities Commission for additional funds to address wildfire threats, regulators said.
But after a wildfire killed two people, destroyed 475 homes and scorched 70,000 acres in the Sierra Nevada foothills in September, homeowners and their attorneys are asking whether San Francisco-based Pacific Gas & Electric Co. did enough to clear dry trees flanking its power lines.
Barry Anderson, a PG&E vice president, acknowledged in mid-September that the fire could have been sparked when a pine tree "may have contacted" a PG&E line.
More than 50 victims have sued PG&E and its tree-trimming contractors for property damage. One suit blames the companies for the death of an 82-year-old man.
PG&E spokesman Joe Molica said the company had spent $260 million to prepare for extreme weather and drought.
State fire officials are still investigating the cause of the blaze.
Nationally, fragmented data collection makes it difficult to gauge whether utilities have adequately hardened their systems against more extreme weather. Many companies are not required to provide regulators with data related to how often outages occur or how long they last.
AP largely adopted the methodology used by independent research organization Climate Central to chart the latest growth in the number of weather-related outages. Climate Central's previous study, spanning 2003 to 2012, found weather-related outages were becoming much more frequent.