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Because streets, parking lots, and buildings are impermeable, city centers are more prone to flooding than other areas, meaning water cannot seep into the ground as in a forest or grassland. Instead, it flows.

Detroit, like many old cities, struggles by combining run-off rainwater with sewage. This mixture is then pumped to treatment plants. During the last storm, power outages and mechanical problems disabled four of the 12 pumps at the two major pumping stations.

Over the past few years, the agency has spent $10 million just to upgrade these two pumping stations and hundreds of millions of dollars for other improvements. However, fully modernizing the sewer system would require building a separate stormwater network at a cost of over $17 billion.

Rainwater infrastructure across the country is aging, and many governments have turned to Band-Aid solutions instead of creating more flexible systems, he says. Michael ChesterA researcher in infrastructure and policy at Arizona State University, Dr. Chester adds that mechanical and electrical systems must occasionally fail during major storms.

But even if the pumping stations were working perfectly, they might not be able to prevent catastrophic flooding.

outdated models

Similar to Detroit’s many stormwater infrastructures, its pumping stations are designed to withstand a 10-year storm, which means precipitation in an hour is about one in 10 in any given year. A 10-year storm in the Detroit area would mean about 1.7 inches of precipitation in one hour, according to National Weather Service data.

During the June storm, parts of Detroit saw heavy rainfall levels that would be more characteristic of a 1,000-year storm (more than 3.7 inches of rain in an hour), well beyond the capacity of the pumping stations, according to the water authority.

However, precipitation forecasts are based on historical data that may not represent the true probabilities of major storms. Anne Jefferson, a hydrologist at Kent State University. Storms, which are assumed to have a one in 10 chance of occurring in any given year, are now more frequent due to climate change. And he says very few institutions take climate change into account in their infrastructure designs.

“We lock ourselves into a past climate,” Jefferson says.

Governments hoping to take climate change into account when designing infrastructure face uncertainty – should they plan for best-case emissions scenarios or worst-case scenarios? And exactly how emissions will affect precipitation is difficult to predict.

Planning larger storms is an admirable goal, but it’s also costly. Chester says larger pumps and pipes are more expensive to build and more difficult to install. And the price increases are not linear, he adds – a pump or pipe with twice the capacity will in most cases be more than double the price.

fast forward

Coastal cities face even more severe climate threats, and some are investing aggressively to fend them off. Tampa, Florida, spent $27 million improving pumping stations and other infrastructure after major flooding in 2015 and 2016. Tampa Bay Times. Some improvements seem to be working – at least this year the city avoided flooding during major storms like Hurricane Elsa.

However, rising seas along Tampa’s coastline may soon shut off the pumps’ outlets. If sea levels reach the point where water needs to come out of storm pipes, the system cannot draw water from the city.

Some cities want to install other features, such as storm ponds and rain gardens, to help manage urban flooding. Grassy areas such as rain gardens can reduce the volume and velocity of excess water, Jefferson says. If enough of these facilities are built in the right places, they can help prevent smaller floods, he adds, but like other stormwater infrastructure, they’re generally not designed to stop flooding during larger storms.