Boulder County, Colorado, gained a new understanding of infrastructure and citizen vulnerabilities from Atkins' City Simulator.

The costliest natural disaster in Boulder County, Colorado, began with a clash of meteorological titans.

In September 2013, a warm front moving in from the south slammed into a lingering cold front.

The collision opened the skies, triggering five days of torrential rains and catastrophic flooding in the state's Front Range region, from Fort Collins to Colorado Springs. More than 17 inches of rain fell over Boulder County. Nine people died, nearly two thousand homes were destroyed, and roads were washed away, cutting off access to mountain communities.

Over just 48 hours, the county received the same amount of rainfall it usually sees in a year. "We get a lot of localized flash flooding—that's normal around here," said Stacey Proctor, a project manager for Boulder County. "But this storm affected the entire county."

The storm indelibly altered the landscape of the region. In Jamestown, situated in the center of the county, cascading water from the mountains overflowed James Creek with enough force to tear in half a home situated on its banks.

In the aftermath, county officials launched a resiliency study of the area, which was completed in November 2019. "We were looking at things that we could do from the perspectives of floodplain management and public infrastructure, which for the county is mostly roads," Proctor said. "And we wanted to take into account that due to climate change, the past is not necessarily predictive of the future."

This is the conundrum. Climate change increases the likelihood of extreme weather events in some locations, but the unprecedented nature of the climate crisis also makes it difficult to predict the details of these events.

Anyone who's played the game Sim City is familiar with the concept of modeling urban and regional development. Reflected in practice as geodesign, it provides a framework for testing alternatives, understanding their impacts, and visualizing their outcomes. This framework, coupled with City Simulator, an analytics software platform developed by the multinational engineering and design consultancy (and SNC-Lavalin Group member) Atkins using Esri technology, takes the concept to a new level.

Among the findings for Boulder County, the data suggested that more 2013-level floods in the Front Range were possible in the coming decades and that even infrastructure originally constructed to withstand once-per-century weather events may need upgrades.

"I think people have been surprised at how many things that have been built to a hundred-year flood level, like bridges, the model shows being flooded," Proctor said. "The question becomes, should we build above 100 years? Because that's not necessarily something we'd do on our own. That's where engineering guidelines may need to catch up to climate change."

As Bourne sees it, modeling and visualization make these questions easier to confront, if not answer. "If we provide the kind of information that moves the needle," he said, "we have the power to take action."

Learn more about how GIS helps governments and businesses analyze weather data to model the impact of and adapt to climate change.

Although the original impetus for creating Atkins' City Simulator was to give governments a tool to understand the effects of climate change, the software is flexible enough to consider other calamities. That includes the epidemiological crisis currently gripping the planet.

"Atkins has a long heritage of flood modeling, which is why we started there," said Bourne "But we've always planned to move on to include other things on our disaster road map, including landslides, wildfires, earthquakes, and pandemics. COVID-19 has pushed pandemics to the front of the line."

At the root, City Simulator simulates residents. To better model how disasters affect lives, the program considers an area's population size and dispersal. Each person is an individual dynamic agent within the program.

This emphasis on movement allowed Bourne's team to model the cumulative effects of disasters. Flooding, for instance, damages roads—yielding direct economic costs—but also makes it difficult for people to commute to work on those roads.

"Our model looks at remoteness. For people in the mountains, if their road is out, they're not going to work that day. Whereas if you're in the urban environment, you can find another path, and maybe you're a half-hour late. We model all of that," Bourne said.

Movement implies contact, so it's no stretch to imagine how human interactions can spread an infectious disease—or how various mitigation strategies can help limit the spread. Bourne's team adapted the Susceptible-Infected-Recovered (SIR) model—used by the World Health Organization and Centers for Disease Control and Prevention—which divides populations into susceptible, infected, and recovered communities. Key to the model is an understanding of how an individual's SIR categorization changes over time, a dynamism City Simulator emulates.

"We were able to build a prototype of that in two weeks," Bourne said. "We're finding that because we chose to simulate the most basic activities first - like human interaction - the subjects we can model are boundless."