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It Rains, It Pours (and a lot more)

Writer's picture: Jun ParkJun Park

Cities need to be redesigned to handle our changing climate


Toronto recently experienced record rainfall this month that wreaked havoc on the city. With nearly 100 mm of rain pouring down, parts of the city became submerged and knocked out power to more than 170,000 residents. The city estimates that the damages from the floods exceeded one billion dollars, with full damage assessments still being conducted from the time of writing. This year has already been one of the wettest years in Canadian history, and experts warn that these “anomalies'' will become more of a regular occurrence.


In Canada alone, weather-related disasters have ballooned from a mere $8.5 billion in the 1970s to an average of $112 billion between 2010-2019, a 1250% increase. This year also marked the first time global warming exceeded 1.5 degrees Celsius above the pre-industrial benchmark over 12 months. It is no surprise that heat records are being broken every single month so far in 2024 and is slated to be the hottest year on record


Source: Carbonbrief

Some impacts of global warming are more obvious, such as hotter temperatures, more intense droughts, and water shortages—while this is true for certain regions, other regions have the opposite problem of inheriting a wetter and more humid climate. Today’s article will focus solely on extreme rainfall exacerbated by climate change as trying to cover all the ill effects of the phenomena will be an endeavor saved for another time (maybe soon to be found here).


Why does it rain more?

Here we take a quick trip back to middle school(?) science class; rain occurs as the water gets evaporated from bodies of water which then condense in the atmosphere. Once condensation occurs, the water then falls back to earth creating rain. Traditionally, rainfall has been relatively consistent with a few anomalies here and there; however, with a warming climate, rainfalls have become more sporadic and harder to predict. It is estimated that for every degree rise in average temperature, the atmosphere holds roughly 7% more moisture, resulting in heavier rainfall and amplifying the effects of greenhouse warming, creating a positive feedback loop, causing even heavier rainfall as time goes on. 


Source: DW

It has been a wet year so far (and it will continue to be so)

Just this past April, the Brazilian state of Rio Grande do Sul experienced one of its worst flooding events resulting in over 100 deaths, 695,000 people being displaced, and over $2.2 Billion in damages. The region received a staggering 150 to 500mm of rain, which experts say has been exacerbated by higher-than-average temperatures and humidity levels. Not only in Brazil, but around the world many countries are experiencing their wettest year in decades, with major floods occurring in Germany, Switzerland, the United States, the United Arab Emirates, England, China, and Canada. This is becoming a widespread phenomenon all over the world with the number of people living in areas with high flood risk increasing 122% since 1985. 2024 has also been a particularly wet year due to the El Niño weather cycle that has warmed the oceans since May of 2023, amplifying the effects of the weather cycle and resulting in more extreme weather patterns. Despite being an El Niño year, many scientists agree that even with El Niño subsiding, human-induced climate change will continue to amplify the effects of extreme weather patterns. With “extreme weather patterns” becoming more of a regular occurrence, many cities around the world should be particularly concerned as a vast majority of large cities reside on flood plains or high-flooding areas. A study conducted by the World Bank shows that, since 1985, urban settlements in “very high risk” flooding areas have increased by 160%, exposing more than 1.8 billion people or 23% of the entire world’s population to flood risks


Source: Worldbank
Source: World Bank

Living with Water

Given that floods are amongst the most destructive natural disasters, more people are living in flood-prone areas, and with the likelihood of flooding events increasing every passing year, there is a very clear need for us to drastically (and rapidly) improve our urban centres in order to make them more resilient to floods. As seen from Toronto recently along with floods in various other cities, urban centres currently are not designed to handle such intense rainfall. One of the predominant factors that worsen flooding effects in cities is pavement. Unlike natural soil, pavement prevents the water from being absorbed and quickly runs off into the nearest body of water, creating flash floods and worsening flooding in urban areas. This rapid runoff of water quickly overwhelms the city's water infrastructure which many are now considered outdated. For example, Detroit’s infrastructure has been designed to handle “10-year” storms—meaning heavier than usual rainfall that is expected every 10 years or so, amounting to the infrastructure roughly being able to handle 1.7 inches of rainfall per hour. However, in June of 2021, Detroit experienced one of its heaviest rainfalls where more than 3.7 inches of rainfall poured down on the city, quickly overwhelming the city’s infrastructure and resulting in heavy flooding throughout the city.


Due to these flooding events happening more often, cities around the world are racing to update their outdated infrastructure and redesign their cities to be more sustainable. One of the most innovative concepts in recent years has been “sponge cities.” Sponge cities or the “sponginess” of a city refers to how much water a city is capable of absorbing and how quickly it can dispense that water to prevent flooding events. The sponginess of cities can be determined by balancing three different factors: blue (ponds and lakes), green (grass, trees, vegetation), and grey (buildings and hard surfaces). Cities that are more prone to floods are usually lacking in either blue or green factors and are dominated by grey ones, which leaves little to no room for water to be absorbed or dispersed, and results in the flooding of urban centres. Auckland, New Zealand, has been crowned the most spongy city in the world; despite being the most populous city in New Zealand, Auckland is rich with various blue and green spaces that help absorb and dispense water quickly resulting in the city being resilient to flooding events. It is important to note that Auckland’s soil is also much more “sandy” compared to cities like Sydney which have much more “dense” soil making it less absorbent. However, Auckland has made an effort to preserve and maintain its green spaces which further help mitigate flooding risks. Various other cities around the world continue to expand their green space, for example, Bangkok finished constructing “Monkey Cheek” parks, a collection of parks designed to increase green space and help the city become more resilient to flooding. The most notable is Chulalongkorn University’s Centennial Park, an 11-acre or 45,000 square metre park that has been designed to capture roughly one million gallons of water (3.7 million litres) in addition to underground tanks capable of storing 160,00 gallons (606k litres) of water to prevent extreme flooding. 


While some cities like Auckland are blessed with vast amounts of green space, most cities do not have that luxury. Cities like New York City (NYC) which is known as the “concrete jungle” have limited green space and are dominated by grey infrastructure; despite this, NYC is among one of the spongiest cities in the world. NYC is often prone to flooding as it is surrounded by water and has very limited green space. As a result of Hurricane Sandy which cost the city more than $19 billion in damages, the city has embarked on one of the most ambitious urban resiliency projects named the “Big U,” a 2.5 billion dollar project that aims to drastically reduce the impact of flooding in the city. The Big U consists of various flood resiliency projects that will create 5.5 miles of new park space that is specifically designed to protect over 60,000 residents and billions of dollars of real estate from sea level rises and storm surges. One of the notable projects is the East Side Coastal Resiliency (ESCR), which is currently underway to raise the elevation of parks in conjunction with the installation of floodgates, floodwalls, and improved drainage infrastructure to protect the most vulnerable part of the city. 


Surprisingly during my research, I found that Toronto is one of the spongiest cities in the world, characterized by its vast green space and numerous channels of water flowing into Lake Ontario. However, unlike NYC, Toronto’s soil profile is way less sandy, which increases runoff. The problem with Toronto is similar to NYC with its old infrastructure; just like Detroit, the city’s sewage and water infrastructure is in dire need of upgrades and is simply not designed to handle the influx of water we have been receiving in recent years. Thankfully, the city is already working on upgrading its infrastructure with a $3 billion investment that is “the largest stormwater management program in the city’s history.” The city is developing 22 km of tunnel systems that will store stormwater and redirect it to a new pumping station that is set to be completed in 2034. In addition to this major project, the city is also working on retrofitting the various sewers and underground storage tanks throughout the city. Toronto is also working on expanding green space throughout the city which will not only provide additional protection from floods but also help reduce air pollution and improve the overall livability within the city. 


As we have seen in previous years, floods are becoming a norm in many parts of the world and will have the most impact in dense urban areas situated in flood plains. Unfortunately, there is no “one-size-fits-all” solution; however, as we can see above, cities can become more resilient through various infrastructure upgrades and by expanding green space. The efforts seen around the world are very encouraging and a lot of progress has been made; despite this however, if we continue to let climate change take its course unmitigated, no matter how much money and effort we throw into upgrades and resiliency projects, the force of nature will always come out on top. 

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