After leaving a path of destruction in Louisiana, Hurricane Ida rocked the Northeast United States. The Philadelphia region experienced record-breaking flooding, leaving roads underwater, power outages, SEPTA service suspended, basements flooded, more than $100 million in damage for Pennsylvania alone, and at least 43 dead across Pennsylvania, New Jersey, New York, and Connecticut.

This wasn’t the first time this summer that extreme weather made headlines. In mid-August Hurricane Henri set rainfall records in New York, left thousands without power from New Jersey to Maine, and caused $12 billion in damage in a region that faces rising hurricane threats.

» READ MORE: After Ida destroyed hundreds of Pa. homes and caused more than $100 million in damage, residents await disaster relief

While water has been a major destructive force this summer, it has driven urban growth, commerce, and globalization for much longer. It is no coincidence that many of the world’s greatest cities, from New York to Tokyo, are adjacent to bodies of water. However, climate change has made this asset a growing liability. Philadelphia and many other of the world’s coastal cities must adapt, or fall to waters that made them great.

Water has always played a substantial role in shaping the urban form. The invention of agriculture paired with the efficient means of transportation that rivers and oceans provided allowed cities to supply enough food to meet the demands of growing populations. Water-based trade routes allowed ancient cities, like those found in the Greek and Roman empires, to grow from small settlements to centers of commerce, culture, and power.

The ability to provide clean water and dispose of contaminated water also proved critical in supporting urban life. The supply of clean drinking water and the construction of sewer systems allowed urban populations to grow and minimize disease caused by unsanitary conditions and polluted water. While ancient Rome constructed aqueducts and sewers more than a thousand years ago, many modern cities could not provide these systems at a large scale until the 19th century. London’s sewer system was not completed until the 1860s, after multiple cholera epidemics and unbearable smells forced Parliament to take action. Despite much of the world’s urbanization being driven by access to these resources and continued access being essential to sustainable urban growth, 700 million urban residents still live without improved sanitation and 156 million live without clean water sources.

“Coastal and riverine cities will continue to face frequent and large hurricanes, flash floods, and sea level rise.”

Jonah Garnick

As climate change threatens to drastically impact the world’s water, these shifts will have profound impacts on cities.

Coastal and riverine cities will continue to face frequent and large hurricanes, flash floods, and sea-level rise. Infrastructure in these cities will be pushed to the brink of collapse, often with catastrophic consequences, as outlined in the latest report released by the Intergovernmental Panel on Climate Change (IPCC). Warming by 1.5 degrees Celsius (2.7 degrees Fahrenheit) is now expected within the next two decades as a realistic best-case scenario, even if emissions substantially decrease. We are already experiencing a taste of what the IPCC predicts: The extreme weather intensified by warming seen this summer will continue to grow in frequency and magnitude, including flash floods, droughts, and hurricanes — all changing and potentially redefining our coexistence with and dependence on water.

We’ve already seen previews of system failures: In Zhengzhou, China, flash flooding along the Yellow River overwhelmed the subway system, trapping more than 500 riders in a subway car, killing at least 12 in July. Philadelphia-area drivers were left stranded as a 100-year flood inundated roadways. Climate change threatens the drinking-water supply in coastal and riverine areas, as flooding can contaminate or destroy treatment facilities and reservoirs, and rising seas can salinize fresh water supplies, making them undrinkable.

While water-adjacent cities are arguably most at risk, cities in arid environments will be transformed by water scarcity. As droughts — and the more frequent, intense wildfires they fuel — become common, life in cities across dry regions like California will become harder. Beyond Los Angeles, cities throughout California from the Silicon Valley to San Diego will continue to face perpetual water shortages, possibly driving large-scale migration.

The areas most safe from the changing relationship between cities and water will absorb the changes. Soon-to-be “climate havens” like Duluth, Minn., may be transformed from small cities into global metropolises within decades as world cities decline and climate migrants flee to higher, cooler, and safer ground.

In broad strokes, these changes are likely if not inevitable. But there are actions cities can take now to redesign and adapt to mitigate the worst effects — and even use water to build a better civilization, as we have done before.

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First, we must invest in infrastructure interventions to flood-proof our cities. In some cases this will be large gray infrastructure, like the seawalls used in the Dutch approach, but we must also prioritize cost-effective nature-based solutions that lessen flood impacts.

Second, we — officials, scientists, and civilians — must improve how we communicate risk. People have to understand the new hazards that may disrupt their lives and be provided with tools and information to protect themselves.

And finally, in some instances, we must not be afraid to retreat. Although this may be the hardest solution to accept, we must eventually come to terms with the fact that a changed climate has transformed areas that we once deemed desirable into places that may now be considered dangerous. We can recover, but we will have to adjust.

Jonah Garnick is a Master of City Planning candidate at the University of Pennsylvania concentrating in land use and environmental planning, and urban resilience.