SEOUL, South Korea — South Korean prosecutors on Sunday indicted impeached President Yoon Suk Yeol on rebellion in connection with his short-lived imposition of martial law, a criminal charge that could incur the death penalty or life imprisonment if convicted.

This is the latest blow to Yoon, who was impeached and arrested over his Dec. 3 martial law decree that plunged the country into political turmoil, shook its financial markets and hurt its international image. Separate from criminal judicial proceedings, the Constitutional Court is now deliberating whether to formally dismiss Yoon as president or reinstate him.

Yoon has become South Korea’s first president who has been indicted while in office. He will remain jailed and be escorted from a detention facility to a Seoul court for hearings in the trial, which is expected to last about six months.

Prosecutors said in a statement that they indicted Yoon on charges that he directed a rebellion when he imposed martial law. Investigative authorities have earlier alleged that Yoon’s imposition of martial law amounted to rebellion, because he staged riots with the purpose of undermining the constitution.

Yoon’s defense team lashed out at the indictment, calling it “the worst decision” by prosecutors who they say are trying to curry favor with political forces who want Yoon’s exit.

“Today’s indictment of the president will remain as a shame in the history of South Korean prosecutors that they cannot erase,” Yoon’s defense team said in a statement. “We stress once again that a president’s declaration of martial law can never be rebellion.”

Yoon has presidential immunity from most criminal prosecutions, but the privilege doesn’t extend to allegations of rebellion or treason. By law in South Korea, the leader of a rebellion can face a life sentence or capital punishment.

Yoon, a conservative, has steadfastly denied any wrongdoing, describing his declaration of martial law as a legitimate act of governance meant to raise public awareness of the danger of the liberal-controlled National Assembly, which obstructed his agenda and impeached top officials. During his announcement of martial law, Yoon called the assembly “a den of criminals” and vowed to eliminate “shameless North Korea followers and anti-state forces.”

After declaring martial law on Dec. 3, Yoon sent troops and police officers to the assembly, but enough lawmakers still managed to enter an assembly chamber to vote down Yoon’s decree unanimously, forcing his Cabinet to lift it.

The martial law imposition, the first of its kind in South Korea in more than four decades, lasted only six hours. However, it evoked painful memories of past dictatorial rules in South Korea in the 1960s-80s when military-backed rulers used martial laws and emergency decrees to suppress opponents.

South Korea’s constitution gives the president the power to declare martial law to keep order in wartime and other comparable emergency states, but many experts say the country wasn’t under such conditions when Yoon declared martial law.

Yoon insists that he had no intentions of disrupting assembly work, including its floor vote on his decree and that deploying troops and police forces was meant to maintain order. But commanders of military units sent to the assembly have told assembly hearings or investigators that Yoon ordered them to drag out lawmakers to prevent them from overturning his decree.

Investigations on Yoon have intensified the country’s already serious internal division, with rival protesters regularly staging rallies in downtown Seoul.

After a local court on Jan. 19 approved a formal arrest warrant to extend Yoon’s detention, dozens of his supporters stormed the court building, destroying windows, doors and other property. They also attacked police officers with bricks, steel pipes and other objects. The violence left 17 police officers injured, and police said that they detained 46 protesters.

Yoon earlier resisted efforts by investigative authorities to question or detain him. He then was apprehended on Jan. 15 in a huge law enforcement operation at his presidential compound.

Leading Yoon’s investigation was the Corruption Investigation Office for High-Ranking Officials, but Yoon has refused to attend CIO questioning sessions since being detained, saying it has no legal authority to investigate rebellion allegations. The CIO has said that it can investigate Yoon’s rebellion allegation because it’s related to his purported abuse of power and other allegations.

The CIO handed over Yoon’s case to the Seoul prosecutors’ office on Friday and asked it to indict him on charges of rebellion, abuse of power and obstruction of the National Assembly. Prosecutors said they indicted Yoon only on rebellion, considering that Yoon had presidential immunity from other charges.

Yoon’s defense minister, police chief and several other military commanders have already been arrested on alleged rebellion, abuse of power and other charges related to the martial law decree.

If the Constitutional Court rules to drive Yoon out of office, a national election to choose his successor must be held within two months. Recent public surveys show that governing and opposition party candidates are running neck-and-neck in a possible presidential by-election race.

With more rain on the way, officials warned Sunday of an increasing risk for mudslides in Los Angeles County’s burn areas, with a 10% to 20% chance of significant flash flooding and debris flows capable of damaging roads and homes in and around areas devastated by wildfires.

“This is the worst-case scenario to prepare for,” said Kristan Lund, a meteorologist with the National Weather Service in Oxnard.

“We do have increasing concern for the burn scars,” Lund said. The charred footprint of the Eaton fire, which blackened more than 14,000 acres, is the most worrisome. “These flash floods and these debris flows could happen in and near or below these burn scars.”

A flood watch took effect at 10 a.m. Sunday and will continue through 4 p.m. Monday for the burned areas of the Eaton fire in the Altadena and Pasadena areas; the Palisades and Franklin fires in the Pacific Palisades and Malibu areas; the Hughes fire around Lake Castaic; and the Bridge fire in San Gabriel Mountains west and southwest of Wrightwood. The flood watch started six hours earlier than originally anticipated.

“The highest risk for debris flows would be after 4 p.m. Sunday,” the weather service said.

If you’re not sure you’re near enough to the burn scar, “assume that you are,” Lund said. However, a city like Montebello — roughly 10 miles away from the burned area of the Eaton fire — is not considered close.

“If you’re close to the fire, you want to be on the prepared side,” Lund said. Steps people can take are to avoid being in or around the area from Sunday afternoon through Monday afternoon; using sandbags to protect property; and, for people who do decide to stay, stocking up on supplies in case road access is blocked.

A “landslide” is an all-encompassing term that can describe any movement of rock, dirt or debris downhill. A “debris flow” can happen when water rapidly flows downhill and, besides mud, picks up rocks, branches and sometimes massive boulders. This is also considered a type of shallow landslide, which can occur with potentially deadly force.

Animated infographic shows a debris flow works

Landslides are a risk after wildfires because the heat of the fire makes the soil repellent to water. When rainfall intensities are high — falling at more than one-half an inch per hour — water can start flowing on the surface downhill, instead of percolating below ground, and can begin to pick up rocks and debris.

“It really has to do with the track of the storm,” Lund said. “They’re the greatest potential for significant debris flows. They’re the most recent burn scars; they’re close to communities or vulnerable infrastructure.”

The orientation of the terrain is also vulnerable in this particular storm. The burn scars are over mountain slopes that face the south, and the moisture from the storm is being pulled in from the south, forecasters say.

Those factors could cause “some more heavier rainfall in those areas,” Lund said.

Forecasted rainfall totals for the three-day storm continue to tick upward. Through Monday, Covina could get 1.32 inches of rain; downtown L.A., 1.14 inches; Long Beach, 1.12 inches; Canoga Park, 1.05 inches; Santa Clarita, 1.04 inches; Fillmore, 1.02 inches; Redondo Beach, 0.95 inch; and Thousand Oaks, 0.87 inch.

(National Weather Service)

Besides the risk for debris flow, there is a potential for waterspouts over the ocean, as well as damaging winds, and strong thunderstorms, Lund said.

And heavier rain can still happen even if you don’t see lightning or hear thunder. But if you do hear or see a thunderstorm, “you’ll likely have higher rainfall rates,” Lund said.

There’s a 15% to 25% chance of thunderstorms developing across a swath of Southern California that includes the recently burned areas, said Carol Smith, a meteorologist with the weather service. Thunderstorms could bring a chance of rainfall rates of half an inch per hour to three-quarters of an inch per hour in isolated areas.

Rainfall rates that exceed one-half an inch per hour can trigger debris flow in burned areas.

Smith said the Palisades fire burn area could see more than an inch of rain; the Eaton fire burn area could get up to 2 inches.

(National Weather Service)

Light rain began falling across the region Saturday night.

The storm will bring the first significant rain of the year. Much of Southern California is in “severe drought” with some areas in the southern most part of the state in “extreme drought,” according to the U.S. Drought Monitor.

Officials advised residents in burn zones to use sandbags to direct runoff and protect property, clear drainage paths, heed evacuation orders and stay off roads covered with debris. They also said residents should keep trash cans and vehicles off the street to allow stormwater to travel freely and avoid contact with polluted runoff.

“If emergency officials say to avoid a certain area, please do that,” Smith said.