The article talks about Tokyo being designed to handle 5 cm/hr of rain. That's extreme but not record breaking. The rate given for the Edo Discharge Channel pu

The article talks about Tokyo being designed to handle 5 cm/hr of rain. That's extreme but not record breaking. The rate given for the Edo Discharge Channel pumps in the article is 200 tons per second. At 5cm/hr, that's enough to drain a region 150km x 100 km, or the whole Tokyo metropolitan area. There are other drains (like the Edo River itself) and other sources of rainfall, but based on that calculation 200 tons per second is a huge contributor to draining even a megacity.