Climate change and population growth have led to a worldwide surge in the number of people exposed to hazardous levels of heat, according to a sweeping study that examines 13,115 cities from 1983 to 2016.

Why it matters: Extreme heat is the top weather-related killer in the U.S. each year, and studies show that as the world continues to warm in response to greenhouse gas emissions, heat exposure will become so severe that it will reduce economic output in many regions.

Tropical Cyclone Shaheen killed at least nine people as it slammed coastal areas of Oman and Iran Sunday, the BBC reports.

Of note: Shaheen is the first tropical cyclone to ever hit Oman's far north, as it triggered flash flooding and heavy rains — with some areas of the desert climate seeing over a year's worth of rain in one day, Yale Climate Connections notes.

U.S. Geological Survey scientists confirmed that Hawaii's Kīlauea volcano began erupting Wednesday within Halema'uma'u crater, the summit of the volcano.

Why it matters: Kīlauea's major eruption in 2018 destroyed more than 700 homes, displacing thousands of people and devastating residential areas in the Puna District on the Big Island, according to the National Park Services.

Volcanic explosions on the Spanish island of La Palma intensified on Friday after a new vent opened, forcing firefighters to retreat and three more towns to evacuate, Reuters reports.

Why it matters: Mount Cumbre Vieja erupted earlier this week, destroying hundreds of homes and forcing thousands to evacuate, Reuters reports. Firefighters had been scheduled for clean-up work on Friday before the latest explosion.

Two wildfires were threatening California's sequoia trees overnight — hours after authorities issued fresh evacuation orders and warnings, along with air quality alerts.

The big picture: Air quality alerts were issued Wednesday for the Bay Area and the San Joaquin Valley as smoke from the Windy and KNP Complex fires resulted in hazy, "ash-filled" skies from Fresno to Tulare, the Los Angeles Times notes.

About 5,000 people, including 500 tourists, on the Spanish island of La Palma, have been forced to evacuate after a volcano, known as Mount Cumbre Vieja, erupted Sunday, Reuters reports.

Driving the news: The explosion, which took place in a southern area of the island known as Cabeza de Vaca, came after several weeks of seismic activity, with authorities recording an earthquake of about 3.8 magnitude before the eruption.

The KNP Complex Fire, which reached the western edge of Sequoia National Park Saturday night, has so far spared a group of giant sequoias, local authorities said on Sunday.

Why it matters: The forest contains over 2,000 giant sequoias, including one that is considered the largest tree on Earth by volume. The giant trees are considered "national treasures," and protective measures, such as wrapping portions of the trees in fire-resistant foil, are in place to curb damage.

Southwest Louisiana faces a "high risk" of flash flooding from Tropical Depression Nicholas on Wednesday morning, the National Weather Service warned.

Why it matters: Such "high risk" outlooks are rarely issued anywhere in the U.S. There's also a medium risk of flash-flooding in New Orleans, which is still reeling from Hurricane Ida striking the state last month.