A relatively narrow peninsula with the Atlantic Ocean on one side and the Gulf of Mexico on the other, projecting out in the direction most hurricanes approach from, full of rivers and lakes, and composed largely of highly porous limestone -- Florida is like a sponge soaking in a full sink. A superabundance of water falls from the sky and rises from the ground. The probability of flooding in many areas, especially those near both large and small bodies of water, is anticipated the way people prepare for winter storms in the American Midwest, or droughts and further west. It's not a question of if, but when it'll happen again, and how bad it'll be.
The likelihood of flood events makes it important to prepare by understanding which areas are likely to flood, and what people should do when that happens. It's also good to realize that flood events don't affect everyone equally, and can create different problems for people in various locations and socioeconomic situations. In a series of maps, we'll consider how environmental factors meet with certain human factors by superimposing demographic data over the areas prone to flooding in the low-lying Jacksonville area. Click to enlarge.
This map shows flood risk zones in shades of blue, with locations of interest signified by X shaped symbols. The scope is a little north and south of greater Jacksonville, which is encircled by freeways shown as white lines. The map has a portrait orientation so it can show a greater portion of the ocean shoreline and the banks of the St. Johns River.
The legend indicates three types of important locations, the first two being storm shelters inside and outside of Duval County. According to First Coast News 2019, these were the shelters that people were instructed to use during Hurricane Dorian, most of which are schools. The third type of location is correctional facilities, juvenile and adult, because when extreme weather threatens an area it's important to remember, but easy to forget, the individuals who don't choose whether they will evacuate; that decision is made by those responsible for the facilities.
Below these, the legend shows the dashed line indicating county boundaries. Flood zone data from FEMA is broken down into three categories. Regulatory floodways, in a dark turquoise color, are areas along the channels of water bodies, like rivers or streams, that are reserved to give excess water a place to go without increasing the flood elevation. Very little is to be built in these areas, to avoid local flooding problems. The 1% Annual Chance Flood Hazard, in a medium blue, is the same as the "100 Year Flood," and refers to the areas that have a 1% chance of flooding in a given year. The 0.2% Annual Chance Flood Hazard is the area beyond which has a 0.2% chance of flooding in a given year. Taken together, we get a picture of how water encroachment tends to happen in and around Jacksonville, in other words, the places where water is expected to accumulate in excess. This means the city can plan for it.
Unsurprisingly, flood zones are frequent along the Atlantic coast, which is just a 30 - 40 minute drive from Jacksonville. Most of the inland flood zones appear near streams and creeks that are offshoots of the St. Johns and Ortega Rivers and smaller bodies of water. Along some of these we see the regulatory floodways that help control water. Notice that there is relatively little flood zone area along the main part of the St. Johns River, compared to the thinner streams. The large part of the river is less likely to overflow its banks because its edges are well fortified in the urbanized areas along it, and the further you get from the river, the more ground the water can pool in before finding a place to drain. We also see significant flood zones along the north edge of the map, around the Timucuan Ecological and Historical Preserve right before the St. Johns River meets the Atlantic, and at the Nassau Valley Outstanding Water areas. These are examples of Florida's lowest-lying landscapes, where fewer people live; the ecosystem is prepared to handle flood events naturally.
This next map can help us compare these flood zones to the places where people live. Click to enlarge.
This map presents the flood zones consolidated into one color, with population density superimposed in glowing orange. Now we can see where the people are, and where they're not. As I write this discussion, I'm sitting somewhere a little left of the middle of this map, not far from the river, affecting population density with my mere presence. Wherever you are, you're doing it too! I'm on the porch of a bungalow, which has survived plenty of flood events over the past century because, like many houses in the area, it is elevated several feet off the ground. A lot of residential architecture is like this in Florida, with houses along the beach often being elevated a full story above the ground. Consider it an architectural adaptation, like how houses further north have steep pitched roofs so the snow can slide off.
For a big city, Jacksonville doesn't have an extremely dense population or an incredibly high total population. While it is the most populous city in Florida, it is partly able to achieve that because of its great size. According to the Jacksonville Historical Society, in 1968 Jacksonville annexed several communities and the city and county governments were consolidated for administrative and economic reasons, greatly increasing the size of the city.
Population density per square km is shown by census tract with the most recent data from the American Community Survey. Opacity increases where population density is greater. The most populous parts of Jacksonville do not greatly exceed 2,500 per square km. The map shows population density instead of total population, because the wide variation in the size of the census tracts can give a misleading idea of how populated an area is. Population density gives us a more informative picture of how the people are distributed. We can see sporadic flood zones marbled throughout the most densely population regions. Gaps in the density near certain streams shows how regulatory floodways help keep the distance between the places where people live and work, and the places where flooding happens most consistently, by acting as a designated place for excess water to accumulate. But for the most part, a major storm event will result in some flooding in most of the densely population areas of the city.
People tend to gravitate to bodies of water, big and small, and when the little stream running deep into your neighborhood begins to overflow, chances are that the low-lying roadways have already starting to flood -- the main reason much of the residential architecture has historically been elevated. The ground, very low-lying to begin with, is also highly porous in this part of the country. So building up infrastructure on top of problem areas doesn't tend to fix the problem, because the water collects below with nowhere to go but up and around.
Because water encroachment is an understood part of the terrain, comparatively few people are trying to live in and around the nature reserves on the northern end of the map, where the land is so saturated and so flat that a flood event will easily overflow the network of creeks and streams, and more easily impact a larger area. When all that's being affected is a natural environment prepared to deal with it, flooding is less of a problem.
Sometimes, a storm is severe enough that evacuation can be advised or mandated by the city government. How easily a household is able to comply with this directive will depend on their access to a vehicle and their housing situation, which this next map explores. Click to Enlarge.
This iteration of the map compares the consolidated flood zones to the number of mobile homes and the percentage of households without a vehicle in each census tract. A major storm event is likely to differently affect the people represented by each factor.
Consider the two color bars on the legend. Note that they shouldn't be compared apples to apples, because we are looking at the total number of mobile homes in each tract, and the percentage of households who don't have a vehicle in each tract. In other words, we are using two methods to tell two parts of the story. The total numbers of mobile homes are low enough they get the point across more effectively than percentages would. Both sets of information are the most recent data from the American Community Survey.
The first thing this map can tell us is that most people who live in mobile homes live further from the urban core, and that most households that have no vehicle are closer to the urban core. In lavender, we see that the total number of mobile homes tends to be greater in the more rural areas which the previous map indicated to have lower population density. There are pockets with higher counts of mobile homes between the river and the sea, and in certain medium-sized tracts on the fringes of greater Jacksonville. Note the extensive potential flood zones extending through the broad rural areas at and beyond the Duval County border.
Mobile homes can be a relatively affordable and convenient housing option and, as the name suggests, they come with the advantage of being portable. Given enough time to prepare, mobile home residents can conceivably evacuate with their houses to a safer location. However, if they cannot or do not evacuate, this form of housing is among the most vulnerable to being destroyed by storms. Evacuation will be somewhat easier for people to the north and west of Duval County, where they are already further inland and can make it out of Florida pretty quickly, provided they use US State Roads and Interstates, which are unlikely to be as affected by flooding as the alternative 'backways' will be. So it's important that people who live in mobile homes closer to the ocean are given plenty of notice, so they can get ready and get out before they get stuck behind too much traffic or flooded roadways.
In yellow, we see the percentage of households without a vehicle by census tract. Percentages below 10% have no yellow opacity, and the brightest indicates 50% or more. The brightest yellow spots are downtown and to the north and west of downtown, with relatively high percentages in tracts extending outward from the center. The more populous and urban areas are more likely to be walkable and to have ready access to public transportation compared to rural areas. So living without a vehicle is more feasible than it is in the more sparsely populated areas where a vehicle is a necessity to avoid being stranded. Nevertheless, while it may be more feasible to be without a car in the big city, it's still a major disadvantage, especially to people who have children, who attend higher education, who are seeking employment, or who are trying to evacuate from a storm event.
We can see sporadic flood zones winding indiscriminately throughout the areas where people are relatively likely to be without a car. These people need not only early notice, but also a lot of help to get out of town if necessary to avoid being stuck in their home, where they might experience limited supplies, damage to their home from the storm, loss of power, and the inability to get medical care. Homeless people, who usually do not have a car, fall under this category but should be considered even more vulnerable. It is necessary for provisions to be made to shuttle people who cannot easily transport themselves, either to safe shelters in the city or to be evacuated. Since we live together in a society, we should help each other meet our needs and stay safe.
Let's consider the flood data from one more perspective: the relative income of people in and around Duval County. Click to enlarge.
This map shows the average household income in each census tract, compared to the median, which is currently $66,529. This is the most recent data from the American Community Survey.
Here we have a different type of color bar that's split down the middle. Green indicates an average income anywhere below the median, and pink is above it. Instead of equal intervals, the data is broken into fractions of the median, with the lowest under a quarter of the median, and the greater over twice the median. Lower opacities indicate that the average in a given area is closer to the median, and brighter color indicates greater deviation from it; in other words, the poorest and richest people.
Interestingly, almost every census tract in the greater Jacksonville area, which we've also observed to be the most densely populated, has an average income somewhere under the median, with only a few areas a little bit above it. There is some variation in the more rural areas, most being a little above or a little below the median. On average, the poorest people are in certain segments of the downtown area, and the richest are in certain areas south and east of Jacksonville, especially outside of Duval County and close to the river and the ocean. Waterfront property tends to be sought after, and poorer people tend to gather downtown.
Why does this matter? After all, rain falls on the good and the evil. In theory, when storms affect an entire area, it'll be sink or swim and everybody will experience nature as an equalizing force. But in fact, the same storm will mean very different things for people in different socioeconomic circumstances. We touched on this before when we discussed what a storm event might mean for a person facing transportation limitations. This map indicates that in much of the same area where a higher percentage of households are without a vehicle, there are also lower average incomes. This isn't surprising, and it's reasonable to suspect that those two factors are related. But even with a car, people with lower incomes will have more trouble recovering if their property is damaged or destroyed by a major flood. If they are experiencing housing insecurity, they will be more dependent on the availability and quality of available shelters, and will probably need help getting to one. They are more likely to be uninsured, making them more medically vulnerable to the effects of losing power or of having mold in their homes after a flood. In some areas inferior funding may result in infrastructure being ill-prepared to direct excess water, relative to better-maintained places.
People with a more substantial income are unlikely to experience any of these problems, but a storm will create different kinds of problems for them. Security in transportation, housing, healthcare, and finances means their life and livelihood is less vulnerable to the threat of a storm, although caution and foresight are still as necessary as for anyone else. However, people with higher incomes tend to own the most valuable properties, so even though they are more prepared to repair or replace damaged property, they also stand to lose financially in the event of property damage. Long-term sea level rise could make these 'sometimes' flood zones into a more permanent problem. They are also the most likely to own their property. As indicated by the map, wealthier households tend to be closer to the water, and will face the storm head-on either by rainfall, flooding, or both. The softness of the earth in Florida means that a lot of trees are blown over if there is too much water in the soil, and they often fall on houses or rip up part of the ground with them; this problem can be more severe nearer to the shoreline. It can be a really monstrous scene closer to the beach during a severe storm, and it's important for even the wealthier population to evacuate in a timely manner.
While there's nothing we can do to make cities like Jacksonville impervious to severe storms, or to change the earth in this region so that it's less prone to flooding, it helps to consider the data in order to prepare to help the people who need it the most, to understand the risks we all face, and to have a plan in place. Every storm will create an opportunity to evaluate how well the infrastructural and social measures in place held up under the challenge, and the city will have a responsibility to make improvements where possible. In future maps, we will consider factors like these in other cities where flood events take place, and areas where other kinds of extreme weather affect people.