SIERRA NEVADA REGION, Calif./Nev. – Nearly 30 years ago, unseasonably warm rains melted the snowpack in the Truckee, Carson, and Walker Rivers, bursting over their banks and eventually covering almost 64,000 acres of land over the course of three days. While agencies disagree about how often floods of that size will occur in the area, one thing is for certain—climate change will only make it worse. Now, scientists at the University of Nevada, Reno are developing computer modeling to help cities on the Sierra Nevada front deal with these worsening flood impacts.

Using computer modeling to understand flood impacts isn’t new. In 2011 the United States Geological Survey (USGS) developed a scenario called the ARkStorm, which covered much of California. This scenario spliced together data from historical storms to create an extreme winter storm triggered by atmospheric rivers, hence, AR. The sudden and intense precipitation from such an event is unlikely, but presents a very real possibility that everyone from residents to emergency management services to scientists should consider.

In 2014, the Desert Research Institute (DRI), sister institute of the University of Nevada, Reno scaled down the ARkStorm scenario to the Lake Tahoe Basin, exploring and addressing area-specific needs and concerns. After more severe weather impacts seen in 2017 and 2023, the 2.0 version of this project, called ARkStorm@Sierra Front, aims to use new datasets and models to inform stakeholders of potential flood risks and impacts. Unlike the previous model, ARkStorm@Sierra Front also takes into account new climate data that shows expected effects of climate change on storms in the area.

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Dr. Christine Albano, an associate research professor in hydrology at DRI, is one of the leads of the project. She, along with other scientists and stakeholders, use computer modeling to look at how the new ARkStorm scenario could impact both people and property. They can see where and who might be most affected, what infrastructure and preparations could fail if not updated, and potential paths towards building resiliency in the area.

“The impacts of the ARkStorm in the Tahoe region are very different from other parts of California—there’s tourism and rural areas with limited access, as well as the elevation and snow to consider,” said Albano. Lake Tahoe is at roughly 7,000 feet elevation, which is where precipitation often transitions from rain to snow. But as the climate has been warming, it also leads to warmer storms and changes in snow and rain proportions at high elevations. “Those impacts then accumulate downstream, which is why our 2.0 version of this considers the Sierra Front.”

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But where does the information for computer models like ARkStorm come from? Concrete, current data goes a long way. Having long-standing, historical gauges that measure how high the water goes in a river each season, knowing the temperature of the air and precipitation, and historical records help. And as technology advances, it can make better predictions with more complex calculations.

Other scientific agencies, such as the National Oceanic and Atmospheric Administration (NOAA), collect and provide data for models like ARkStorm, as well as their own predictive weather models for weekly forecasts. Chris Smallcomb, meteorologist in charge at the Reno branch of NOAA, says that computers now do much more to predict weather changes. Now, meteorologists like him can work on the human side of things, providing “decision support services.”

Keeping people informed during storms and floods is no easy task. From the first reports rolling in from weather services, to infrastructural decisions made at key points like dams and floodplains, to emergency services responding to new variables, to the people living in the affected areas—everyone needs accurate information as fast as possible. One of the key things the ARkStorm project did was conduct exercises and scenarios to help unify all these stakeholders.

While conducting these scenarios is standard, ARkStorm@Tahoe brought together over 300 people to work on them. The project then produced a report that enhanced awareness of potential storm risks, improved emergency services responses and communication among stakeholders, and helped scientists better understand how to predict the likelihood of such events.

“The magnitude is hard to fathom and fully prepare for,” said Tim Bardsley, senior services hydrologist at the Reno NOAA branch. “One of the most beneficial parts of an exercise like this is that it generates awareness, especially because the literature supports it being more probable, given the warming climate.”

There’s another issue with flood preparedness that’s psychological. George Robison, executive director of the Truckee River Flood Management Authority (TRFMA), calls flood amnesia. Major storms don’t happen every year, let alone floods on the scale that ARkStorm predicts. “ARkStorm is important for people to understand potential impacts of climate—it gives people awareness of what nature is capable of doing. This river in the desert doesn’t always stay small.”

The TRFMA uses maps to help people understand where floods can reach, which in turn helps determine both emergency actions, such as where to put evacuation centers, and long-term decisions, like what places are appropriate to build structures in. Communication tools like maps can help people understand their risk level for where they live and prepare appropriately.

But for marginalized communities, who often live in high-risk areas, organizations are making active efforts to reach them. Mari Webb, a PhD student working with Dr. Albano on the ARkStorm project, has been funded by the USGS Hazards office to look at the effects on vulnerable and marginalized people in the area.

“The preliminary results of these studies—which look at things like socioeconomic vulnerability based on census data, including poverty levels, income, race, ethnicity, and insurance overlain with flood extents—is that the more frequent, smaller floods affect historically marginalized populations disproportionately, while major floods affect all populations more equally” said Webb. “These more frequent, smaller events accumulate inequity and erode the resources of more vulnerable populations.”

Robison noted that state and federal policies now focus on these groups, providing grants that help support programs and emergency services for them. One of their current target groups is unhoused populations, who often set up near the river. Both the TRFMA and NOAA emphasized that they care about communicating to these populations and ensuring they have the information needed to stay safe during storms. “These communities don’t have the means to do as much, so grants and communication do help. And these factors that put underprivileged communities at risk do matter to us and impact our work.” said Robison.

And as these organizations continue to collaborate with each other, Albano and Robison both talked about pulling in other stakeholders to improve the outcomes of flood preparation. Robison said, “We’re really interested in working with tribal populations around Pyramid Lake because they’re very geared and connected to the lake.”

While the massive flood may not be coming right away, preparing for a real possibility of one can improve how people prepare for them, making smaller floods more manageable. Albano says she hopes that the ARkStorm scenario will continue to unite organizations to help serve and protect communities from these natural hazards, that will worsen as climate change progresses. “We’ve had success with engaging with people in the area in the past, and we want to continue to work with people in our community and demonstrate this as a model for other areas where flood risks are high.”

Eli Ramos is a reporter for Tahoe Daily Tribune. They are part of the 2024–26 cohort of California Local News Fellows through UC Berkeley.