“Après moi, le déluge” – King Louis XV (1710-1774)
Northeast Ohio has a flooding problem, as anyone affected by the severe storms last evening can attest. The region has experienced at least four major flooding events in the past few months, the most serious of which occurred five months ago on May 12, when torrential rains caused widespread flooding in several communities.
As the hydrographs below demonstrate, this severe deluge caused several rivers and streams to overflow their banks throughout the western and southern portions of Greater Cleveland. Flash floods also occurred in several areas; one raging flash flood nearly washed away a vehicle containing legendary meteorologist Dick Goddard, who apparently did not heed that famous National Weather Service saying: “turn around, don’t drown.”
Who is to blame?
Since these floods occurred, people have been looking for answers or, in many cases, someone to blame. Those individuals whose property and piece of mind were damaged by the floodwaters have, in many cases, been understandably and justifiably upset, even angry. Many of these people have turned their anger at their municipal governments for failing, for one reason or another, to prevent the floods from occurring. This anger bubbled over in some instances, leading to highly contentious public meetings, such as the one in North Olmsted during which a resident got on stage to publicly rebuke officials and call for citizens to sue the city. Residents of other municipalities, including Olmsted Township and Strongsville, are also considering class action lawsuits, accusing their cities of negligence for not investing in adequate infrastructure upgrades.
City officials, for their part, have found a different scapegoat – the rain itself. And there can be no question that the rain in some areas in the past few months has been downright biblical. North Olmsted endured 4.44 inches of rain – more rain than it receives, on average, for the entire month of May – in a couple of hours on the 12th. Put another way, that amount of rain would be equivalent to roughly 44 inches of snow. Strongsville, in turn, saw 3.58 inches of rain that evening, just under its monthly average rainfall of 3.66 inches for May.* The following month, Cleveland suffered a similar fate. The 3.54 inches that fell on June 24 made it the fourth rainiest day for the city in the past century.
Yet, major rainfall events are not uncommon for Northeast Ohio during the summer months; in fact, they are the norm. On average, roughly 40% of the total precipitation in the Midwest each year falls during just 10 days; almost all of these days occur during the summer months, when high heat and humidity can lead to major convective storms. But, what is different is the frequency with which these types of flooding events are occurring. Residents in many of the affected communities have testified that they have experienced floods on a semi-regular basis over the past 10-15 years.
Don’t blame it on the rain…or the sewers
While it may be convenient to blame these floods on the rain, it’s not that simple. As the (handful of) people who have perused this blog in the past have no doubt grown tired of reading, there’s no such thing as a “natural” disaster. Rather, disaster risk is the combination of a natural hazard, our physical and economic exposure to the hazard, and our socioeconomic vulnerability. If 4 inches of rain falls in the middle of an uninhabited tract of some national park in Montana, it does not constitute a disaster. In a sense, for disasters, if a tree falls in the forest, and no one is there to see it, it really doesn’t make a sound.
So, while it may make sense for people to blame inaction by public officials or the heavens for floods, these simply represent the proximate causes of the disaster. We cannot hope to address the real issue at hand by focusing simply on these; that is the equivalent of treating the symptoms of the illness. Rather, we need to focus on the root causes, which one can identify through this disaster risk lens.
Since I cannot readily or adequately examine the various facets of disaster vulnerability for every community affected by this summer’s floods, I want to focus instead on the other two components of the disaster risk triad – natural hazards and exposure. Increases in extreme precipitation events due to climate change and Northeast Ohio’s ongoing sprawl problem, respectively, account for much of the apparent spike in flooding events throughout the region over the past several years. I explore each of these below.
Natural hazard: Climate change and precipitation in Northeast Ohio
Logically, the more rain that falls over an area, particularly within a limited period of time, the higher the likelihood that a flood will occur. We already know that, based on simple physics, as global temperatures increase, the amount of moisture in the air should also rise. According to the Clausius-Clapeyron equation, the atmosphere’s capacity to hold water vapor increases roughly 7% for each 1ºC increase in atmospheric temperatures. This should lead to two general outcomes. First, it will take the atmosphere longer to reach its point of saturation, which may lengthen the periods between rain events for many areas, contributing to droughts. Conversely, because the amount of water vapor available for precipitation also rises, rainfall events should become more extreme in nature. As Dr. Kevin Trenberth put it in a 2007 study (PDF),
Hence, storms, whether individual thunderstorms, extratropical rain or snow storms, or tropical cyclones, supplied with increased moisture, produce more intense precipitation events. Such events are observed to be widely occurring, even where total precipitation is decreasing: ‘it never rains but it pours!’ This increases the risk of flooding.
We are already witnessing this intensification of rainfall in the US, particularly in the Midwest. According to the latest National Climate Assessment (NCA), total precipitation has increased in the Midwest by 9% since 1991. Over the past century, certain parts of the region have seen precipitation totals climb by up to 20%. This increase is due largely to a spike in the frequency of extreme precipitation events. From 1958-2012, the amount of precipitation falling in very heavy downpour events jumped by 37% in the Midwest. This statistic helps to explain why, of the 12 instances in which Cleveland received more than 3 inches of rain in a day during the last century, 7 have occurred since 1994.
Unless we take action quickly to reduce our carbon emissions, this situation will only get worse in the coming decades. The NCA projects that, under a business as usual scenario (RCP 8.5), Ohio will see such extreme precipitation events four times more frequently by the end of the century.
Exposure: Sprawl and flooding in Northeast Ohio
Northeast Ohio has suffered from decades of sprawl and uncoordinated development patterns, leading to waves of suburbanization followed by exurbanization. In 1948, Cuyahoga County’s population stood at 1,389,532; just 26% of land in the county was developed at the time. Yet, by 2002, although the county’s population had grown by a mere .32% to 1,393,978, sprawl ensured that roughly 95% of the county’s land area had been developed.
We’ve come a long way since 2002. The heyday of sprawl appears to be on its last legs, as the combined effects of the Great Recession, the rise of the Millennial generation, and the gradual retirement of the Baby Boomers has led to a resurgence in the number of people living in walkable urban areas. Multiple sources have proclaimed the end of sprawl; this trend even appears to be taking root in Atlanta.
Cleveland has tried to position itself to follow this emerging trend. The city was recently ranked 10th most walkable among the largest 30 metro areas, enjoys a 98.3% residential occupancy rate downtown, has unveiled a plan to double the amount of bike routes in the city by the end 2017, and has seen a rise in transit-oriented development.
Given all of these positive indicators, why would I suggest that sprawl has increased the frequency and intensity of floods over the past decade-plus? Well, simply put, because it has. While it’s impossible for one to deny all of these positive indicators, one also cannot ignore the facts.
In its Measuring Sprawl 2014 report, Smart Growth American ranked Cleveland 153 of 221 metros on its sprawl index. The median score was 100; cities with scores over 100 were more compact, while those with scores less than 100 were more sprawling. Cleveland scored an 85.62 (PDF), placing it below other regional metros, including Detroit (12th), Milwaukee (15th), Chicago (26th), Akron (111th), Dayton (116th), Toledo (117th), Pittsburgh (132nd), and Columbus (138). Cleveland does outperform some other nearby metros, including Indianapolis (158th), Cincinnati (166th), and Youngstown (175th).
Moreover, a recent study out of the University of Utah suggests that from 2000-2010, the Cleveland metro area became even more sprawling (PDF). Using Smart Growth America’s sprawl index, the authors examined the rate of change for the 162 largest metro areas (paywalled) during this period. While Akron actually became 2.7% more compact, Cleveland sprawled by another 13.3%, the 10th worst change of any metro area. Though the city’s number improved since 2010, our 85.62 in 2014 is still lower than the 86.01 that we had 14 years ago.
So why does this all matter for flooding? Well, simply put, areas that follow sprawl-based development models are more likely to suffer from flooding problems. Sprawl increases the percentage of land area that is covered with impervious surfaces, such as parking lots, roads, and driveways. As the extent of impervious surfaces rises, so too does the amount of precipitation that winds up as surface runoff during storms. Forested areas are excellent at controlling stormwater (PDF); trees enable 50% of precipitation to infiltrate the soil and allow another 40% to return to the atmosphere through evapotranspiration. Urbanized areas, in contrast, drastically reduce the amount of water that can infiltrate into the soil, guaranteeing that 35-55% of precipitation ends up as runoff.
As Hollis (1975) has shown, urbanization increases the incidence of small flooding events 10-fold (paywalled). Additionally, if 30% of the roads in an urban area are paved, major flood events with return periods of 100 years or more tend to double in magnitude. Northeast Ohio has more than 48,000 acres of impervious surfaces, equivalent to approximately one-third of the region’s land area. Accordingly, we fall directly into that danger zone for major flood events due, in large part, to our development patterns.
Secondly, because so much of the county is already developed, many new developments are being built in existing flood zones. In December 2010, FEMA released its first comprehensive flood zone maps for Northeast Ohio since the 1960s. Unsurprisingly, these maps show a dramatic increase in the number of people living in flood zone areas, due to the outward expansion of development. Thousands of people woke up one day to find out that they had been living in a flood zone, and they were none too happy to learn that they would now have to shoulder some of the cost of that decision by purchasing federal flood insurance. Interestingly, the gentleman who filed the class action lawsuit against Strongsville over the flooding lives in a housing development in one of these flood plains.
Lastly, sprawl directly contributes to climate change by leading to additional greenhouse gas emissions. Suburban areas account of 50% of the US’s total emissions, despite being home to less than half of the population. While households in downtown Cleveland produce just 26.5 tons of GHGs annually, that number skyrockets to 85.6 tons for Gates Mills residents. Because transportation accounts for such a high portion of the average family’s carbon footprint in this region, our sprawl problem has directly resulted in additional carbon pollution.
There is no question that flooding represents a real threat to the quality of life of people living in Northeast Ohio. Those individuals who have been directly affected by it have every right to be upset and to demand answers. Unfortunately, however, it appears that we are losing sight of the forest for the trees. Focusing exclusively on the proximate drivers of these floods may seem like a good idea, but it allows us to escape examining the real, underlying root causes. Until we step up and begin to shift our regional development patterns away from those centered on sprawl and rampant fossil fuel use, this flooding problem will only get worse.