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The winter grassland fire that blew up along Colorado鈥檚 Front Range was rare, environmental scientists say, but similar events may be more common in the coming years as climate change dries grasslands and suburbs grow in fire-prone areas and people continue to spark destructive blazes.

鈥淭hese fires are different from most of the fires we鈥檝e been seeing across the West, in the sense that they鈥檙e grass fires and they鈥檙e occurring in the winter,鈥� said Jonathan Overpeck, a professor in the School for Environment and Sustainability at the University of Michigan. 鈥淯ltimately, things are going to continue to get worse unless we stop climate change.鈥�

Flames swept over drought-stricken grassy fields and neighborhoods northwest of Denver on Thursday with alarming speed, propelled by guests up to 105 mph. Tens of thousands were ordered to flee with little notice.

鈥淚 came out of Whole Foods, which is about a half mile from ground zero, and felt like I had to jump in my car and make a dash for my life as the smoke and wind and nearby flames were engulfing the area,鈥� Susie Pringle of Lafayette said in an email. 鈥淚t was scary!鈥�

Two people were missing as of Sunday and at least seven were injured but no deaths were reported.聽Officials estimated nearly 1,000 homes and other buildings were destroyed.聽At least 991 homes and other buildings were destroyed, Boulder County Sheriff Joe Pelle聽said Saturday: 553 in Louisville, 332 in Superior, and 106 in unincorporated parts of the county. Hundreds more were damaged. The totals include destroyed barns, outbuildings, and other structures, but the vast majority were homes, Boulder County spokesperson Jennifer Churchill said late Saturday.

Many whose homes were spared remained without power while temperatures dropped to the single digits. The blaze burned at least 9.4 square miles.

Utility crews struggled to restore electricity and gas service to homes that survived, and dozens of people lined up to get donated space heaters, bottled water, and blankets at Red Cross shelters. Xcel Energy urged other residents to use fireplaces and wood stoves to stay warm and keep their pipes at home from freezing.

Families filled a long line of cars waiting to pick up space heaters and bottled water at a Salvation Army distribution center at the YMCA in Lafayette, just north of Superior.

Monarch High School seniors Noah Sarasin and his twin brother Gavin had been volunteering at that location for two days, directing traffic and distributing donations.

鈥淲e have a house, no heat but we still have a house,鈥� Noah Sarasin said. 鈥淚 just want to make sure that everyone else has heat on this very cold day.鈥�

Hilary and Patrick Wallace picked up two heaters, then ordered two hot chocolate mochas at a nearby cafe. The Superior couple couldn鈥檛 find a hotel and were contemplating hiking 2 miles back to their home; their neighborhood was still blocked off to traffic. The family slept in one room on New Year鈥檚 Eve.

Both teared up when a man entered the shop and joked aloud that he鈥檇 lost his coffee mugs聽鈥� and everything else聽鈥� in the fire. The man was in good spirits, laughing at the irony of the situation.

鈥淚 have a space heater and a house to put it in. I don鈥檛 even know what to say to them,鈥� Hilary said, wiping away a tear.

Superior resident Jeff Markley arrived in his truck to pick up a heater. He said he felt lucky to be 鈥渏ust displaced鈥� since his home is intact.

鈥淲e鈥檙e making do, staying with friends, and upbeat for the new year. Gotta be better than this last one,鈥� Mr. Markley said.

The cause of the blaze that broke out Thursday is still under investigation, but experts say it鈥檚 clear what allowed it to spread so fast.

鈥淲ith any snow on the ground, this absolutely would not have happened in the way that it did,鈥� said Keith Musselman, a snow hydrologist in Boulder. 鈥淚t was really the grass and the dry landscape that allowed this fire to jump long distances in a short period of time.鈥�

Three ingredients were needed to start this fire聽鈥� fuels, a warm climate, and an ignition source, said Jennifer Balch, a fire scientist with the University of Colorado, Boulder. 鈥淎nd then you add a fourth ingredient, wind, and that鈥檚 when it became a disaster.鈥�

Temperatures in Colorado between June and December were the warmest on record, Ms. Balch said. The grasses grew thick because they had a wet spring, but saw no moisture until snow flurries arrived Friday night.

鈥淎ll of Colorado is flammable, our grasses are flammable, our shrubs are flammable, our trees are flammable,鈥� Ms. Balch said. 鈥淭his is a dry landscape that is flammable for good chunks of the year, and those chunks of time are getting longer with climate change.鈥�

The lesson learned throughout this event is that the 鈥渨ildland-urban interface is way bigger than we thought it was,鈥� Ms. Balch said. That means a wider area is under threat of wildfire.

That border area聽鈥� where structures built by people meet undeveloped wildland prone to fire聽鈥� has always been the foothills, she said. Fire-fighters in Boulder consider the interface west of Broadway聽鈥� a busy road that passes through the center of town. But Thursday鈥檚 fire sparked east of that line, next to thousands of houses that have sprouted up on the east side of the Rockies since the 1990s, Ms. Balch said.

鈥淭here were stretches between Denver and Fort Collins that had no development, but now it鈥檚 just like one long continuous development track,鈥� Ms. Balch said. 鈥淎nd those homes are built with materials that are very flammable聽鈥� wood siding, asphalt roofing.

鈥淲e need to completely rethink how we鈥檙e building homes.鈥�

The other important change is understanding how these fires start in the first place, she said.

鈥淭here鈥檚 no natural source of ignition at this time of year. There鈥檚 no lightning,鈥� she said. 鈥淚t鈥檚 either going to be infrastructure-related or it鈥檚 going to be human caused.鈥�

鈥淭he way we live in the landscape and our daily activities make us vulnerable,鈥� she said.

Over the last two decades, 97% of wildfires were started by people, according to a recent聽study聽by the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder. Causes have ranged from accidents at construction sites, to a car with a hot tailpipe, to tossed cigarettes.

鈥淚 like to say, we need Smokey Bear in the suburbs,鈥� she said. 鈥淲e need to be thinking about how our daily activities can contribute ignitions or sparks that start wildfires.鈥�

Unless people stop climate change by cutting back on fossil fuels, wildfires will threaten communities, Mr. Overpeck said.

鈥淭here鈥檚 little doubt in my mind that the conditions conducive to really bad wildfire, whether it鈥檚 grass or forest, are only going to get worse,鈥� he said.

As more people move to areas where wildfires occur, the threat goes up.

鈥淲e鈥檙e building towns and cities and infrastructure and so it鈥檚 just a matter of time before we have whole towns burning down like we had in California and events like this in Colorado.鈥�

This story was reported by The Associated Press. AP reporter Brittany Peterson contributed to this report.