What Is a Sponge City?

From Grist:

"China’s plan for spongifying its water systems is starting with 16 pilot cities, which will each receive up to 63 million dollars per year over three years for water-related initiatives. According to the Guardian, these projects will likely include developing ponds, filtration pools, and wetlands; building permeable roads and public spaces where rain can soak into the ground; and creating rooftop gardens."