Rainfall intensities for stormwater design in Ontario have been changing over the past 30 years. Data from 13 rain gauges in Ontario show that storm intensities for urban stormwater have increased, with a 1-3% annual increase. For example, a storm that used to occur every 5 years now happens more frequently, and a storm that used to occur every 2 years has also increased. This means that stormwater infrastructure may need to be modified to handle the higher rainfall intensities. In a case study, it was found that 5 out of 12 storm sewer pipes in a subdivision would need to be enlarged to maintain the same level of stormwater performance.