Tag Archives: flooding

Trulia’s mapping tool goes far beyond real estate

You may quibble with how Trulia values your home, but the real estate website provides an impressive interactive map with detailed views of social and environmental variables.

In addition to offering a treasure trove of information on real estate down to the parcel level, Trulia’s mapping engine also visualizes high-resolution data on things like commute times and the risk of wildfires, flooding, and earthquakes.

Below I describe some of my favorite features and share some screenshots. This mapping tool is not without its issues, but it’s generally well-designed and easy to use.

Commute times: driving and transit

One of Trulia’s most interesting features is a layer that maps commuting times. Below are the heat maps for San Francisco, first for driving and then for transit. The two maps are pretty close. Putting aside transit strikes, the Bay Area has a solid system of trains, buses, ferries, and other alternatives to driving, so commuting long distances by transit is feasible, even mandatory, for many residents in the region. These maps don’t account for traffic delays, which is a big caveat. Click on images to enlarge.

San Francisco commute time driving
Source: Trulia
San Francisco commute time transit
Source: Trulia

Compare the pair of images above to the ones below for Las Vegas, where there’s a huge disparity between driving and public transit commuting times. If you give yourself an hour to commute to the city center, being able to drive opens up many more places to live around Las Vegas.

Las Vegas commute driving
Source: Trulia
Las Vegas commute transit
Source: Trulia

Natural hazards mapped

Another useful aspect of Trulia’s map is a collection of natural hazard maps, including depictions of the risks of flooding, wildfires, tornadoes, earthquakes, and hurricanes. One criticism is that the mapping engine doesn’t let you export your views, so you’ll have to rely on screenshots. It’s also difficult to zoom out and see the entire country. You can get around this by zooming out on your browser (press control and the minus sign), which is what I’ve done for the national maps below, but then the text is microscopic. Trulia works best when zoomed in to a region or metro area.


The map below shows wildfire potential across the country and illustrates the inherent risk of an area experiencing a severe blaze under the right conditions.

Trulia wildfire
Source: Trulia

Trulia does a good job explaining its data sources. For the wildland fire potential (WFP) layer, here’s the definition they’re using:

Areas with high WFP values represent fuels with a higher probability of experiencing a high-intensity fire under conducive weather conditions. Areas with low WFP values, therefore, represent a low probability of experiencing a wildfire. The WFP map is maintained by the USDA Forest Service, Fire Modeling Institute, and is intended to be used in analyses of wildfire risk at regional or national scales. The WFP is not intended to be a forecast or wildfire outlook, as it does not include information on current or forecasted weather or fuel moisture conditions.

If you zoom in close enough, the wildfire data also includes perimeters of previous fires. Below is the fire potential around Los Angeles, including the outlines of fires during 2007, a particularly active year. At least in this part of the country, extremely high fire danger areas lie in close proximity to places where the risk is virtually nil.

Trulia wildfire LA
Source: Trulia

If you zoom in to some other regions, the data may get a little funky. Below is a close-up of the Denver area. In the city, the pixelated data suggests that some city blocks have a greater wildfire risk than others, but in reality you’re not going to see a wildfire within the Denver city limits. The map is basically right: as you move west, into the foothills of the Front Range, wildfire potential definitely increases, but at this resolution the map is somewhat misleading.

Trulia wildfire Denver
Source: Trulia


Another limitation is that Trulia is missing data for some parts of the country. In the screenshot below, flood risks suddenly disappear north of Denver. That’s because there’s no data for Weld County. Trulia cautions that even counties with flood data from FEMA don’t necessarily have full coverage.

Trulia flood Boulder
Source: Trulia

Here’s how Trulia describes the high (100-year flood zone ) and moderate (500-year flood zone) risk categories:

In high risk areas, there is at least a 1 in 4 chance of flooding during a 30-year mortgage. All home and business owners in these areas with mortgages from federally regulated or insured lenders are required to buy flood insurance. In moderate risk areas, the risk of being flooded is reduced but not completely removed. These areas submit over 20% of NFIP claims and receive one-third of disaster assistance for flooding. Flood insurance isn’t federally required in moderate-to-low areas, but it is recommended for all property owners and renters.

Although Trulia’s flood risk data may be spotty, covered areas are mapped in great detail, as shown in the map below of Boulder, Colorado, which recently experienced epic flooding.

Trulia flood Boulder zoom
Source: Trulia


Trulia’s tornado hazard map, based on data from the National Weather Service’s Storm Prediction Center, shows that this weather phenomenon is largely absent from the American West. Drill down to the local level and the map shows the tracks of previous tornadoes. Below the national map is the area around Oklahoma City. I chose the month of May, when disasters such as the Moore Tornado of 2013 have occurred. This map uses a technique known as hexagonal binning, which employs a honeycomb grid to aggregate and visualize the data.

Trulia tornado
Source: Trulia
Trulia tornado OKC
Source: Trulia


Trulia’s earthquake hazard map shows potential shaking intensity and the system of faults. Here’s how Trulia summarizes the USGS data:

The data represent a model showing a 10% probability that ground motion will reach a specified level within 50 years. Shaking potential is calculated considering historic earthquakes, slip rates on major faults and deformation throughout the region, and the potential for amplification of seismic waves by near-surface geologic materials … Faults are represented as black lines on the map. Darker lines signify a larger slip rate, which is a measurement of how fast one side of the fault slides past the other side.

Everyone knows California and the West Coast is earthquake country, but I hadn’t realized how many other, inland areas are also susceptible to shaking. Below the national map is a close-up of central California.

Trulia earthquake
Source: Trulia
Trulia earthquake SF
Source: Trulia

Telling stories with Trulia

I was pleasantly surprised by the richness of data in Trulia’s maps. Its main competitor, Zillow, doesn’t have anything that comes close. Even if you’re not in the market for a house or thinking of selling, the website is a useful resource for learning more about your community.

The geography of crime, shown below for the Bay Area, is a bit beyond our bailiwick here at EcoWest, but it’s certainly a key driver of growth and land-use patterns that have major environmental consequences (see this Trulia post for more on these crime maps).

Using Trulia, journalists, NGOs, researchers, and local policymakers can piece together a compelling portrait of a city or region by visualizing geographic patterns in crime, housing, transportation, education, and environmental hazards.

Trulia crime San Francisco Oakland
Source: Trulia

EcoWest’s mission is to analyze, visualize, and share data on environmental trends in the North American West. Please subscribe to our RSS feed, opt-in for email updates, follow us on Twitter, or like us on Facebook.

Climate context for Colorado floods: heavy precipitation, wildfires are on the rise

The heavy rains and flooding here in Colorado have been off the charts, even prompting the National Weather Service to describe the precipitation as “biblical” in its proportions.

At Discover Magazine, Tom Yulsman reports that areas with the highest rainfall totals have experienced a 1,000-year event–a storm that’s expected to occur once a millennium. Check out this graphic from Climate Central:

Climate Central Boulder rainfall
Source: Climate Central

Because the flooding in Colorado is so extreme and generating so much attention, I wanted to offer some context by sharing some graphics and thoughts. Rain and snow totals jump around from year to year, but there seems to be an increasing trend of very heavy precipitation events in the United States.

What’s more troubling is that scientists are projecting even more deluges (and droughts) in the years and decades to come. Warmer air can hold more moisture, and higher temperatures will be increasing evaporation rates, so researchers are expecting extreme storms like the one in Colorado to become increasingly common as climate change manifests itself in the hydrological cycle.

Add the growing intensity of wildfires in the West, which in recent years have charred many of the watersheds that are now flooding along Colorado’s Front Range, and you have recipe for more costly, deadly disasters. I’ll leave it to scientists to sort out whether there’s any climate change fingerprint in this event, but the projections for the future are worrisome because warming is also expected to intensify wildfire behavior in the West.

Trend toward more deluges

The graphic below, from the U.S. Global Change Research Program, shows the percentage increases from 1958 to 2007 in the number of days with very heavy precipitation, which is defined as the wettest 1 percent of events (the original study is here). The trend has been especially pronounced in the Northeast.

Days with very heavy precipitation increasing

The U.S. Environmental Protection Agency has two interesting charts on heavy rainfall trends. The first one shows that extreme one-day precipitation events have been rising in recent years, but there’s a ton of year-to-year variability. The orange line is a nine-year weighted average. EPA notes that “in recent years, a larger percentage of precipitation has come in the form of intense single-day events.”

Extreme one-day precipitation events

The second graphic shows what percentage of the contiguous 48 has experienced much higher-than-normal precipitation in any given year. The trend is more ambiguous in this chart, but there’s definitely been a spike in recent years.

Unusually high annual precipitationColorado in drought

Paradoxically, the torrential rains that we’ve been experiencing in Colorado have come while nearly all of the state is in drought. Below is the latest U.S. Drought Monitor for Colorado. It was released yesterday but based on data through Tuesday. It’ll be interesting to see what this map looks like next week.

Colorado drought monitor

Warming to worsen problem

Looking ahead, we can expect deluges like the one in Colorado to increase in frequency. “Global warming is expected to lead to a large increase in atmospheric water vapor content and to changes in the hydrological cycle, which include an intensification of precipitation extremes,” wrote researchers in this 2009 paper in the Proceedings of the National Academy of Sciences.

Overall, the Southwest and places like the Colorado River Basin are expected to get drier, while the Pacific Northwest is projected to get wetter. Our climate deck , as well as posts on water risk/stress maps and the Colorado River Basin Study, have more on this.

The EPA and Union of Concerned Scientists provide good discussions of the impact of climate change on extreme precipitation events. Flooding causes billions of dollars in damage in the United States annually–in a typical year, it’s the most costly form of extreme weather–so the economic implications of this trend are significant.

In Colorado, the rains are finally letting up in most places and the worst appears to be over. We’ve only received about 3 inches here in Northwest Denver, but that’s actually a whopping total for us. Settlers used to call the western Great Plains the Great American Desert.

The American West has always been a region where residents must navigate between the Scylla and Charybdis of drought and flood, but climate change is making those monsters more menacing. Thankfully, this once-in-a-lifetime storm for parts of the Front Range has only killed a handful of people, but that number could rise. The roar of the Black Hawk helicopter that just buzzed overhead and the stunning images of the flooding are stark reminders that this major disaster will be felt locally for years to come.

Post-fire flooding

There’s also a powerful connection between the worsening wildfire problem in places like Colorado and subsequent flooding, especially during summer, when the North American monsoon taps subtropical moisture and pumps it over the Southwest’s mountainous terrain. Wildfires can incinerate the vegetation that tempers the rainfall and keeps soil in place, thereby dramatically increasing the volume of runoff, sometimes with deadly results downstream. Along the Colorado Front Range, this threat has become a regular feature of the hazardous weather outlook that the National Weather Service publishes.

Climate change is expected to dramatically increase the amount of acres burned in the West, as shown in the graphic below from a recent Harvard study, so if business as usual continues with global greenhouse gas emissions, it looks like the ingredients will be in place for many more calamities like the one we’re now witnessing in Colorado.

Percentage increase in area burned
Source: Xu Yue, Harvard School of Engineering and Applied Sciences


EcoWest’s mission is to analyze, visualize, and share data on environmental trends in the North American West. Please subscribe to our RSS feed, opt-in for email updates, follow us on Twitter, or like us on Facebook.