Climate change will bring more rainstorms, flooding

Wednesday, November 4, 2009

Climate change is having its effect, and residents of western Ontario can expect that last year's sewage bypasses and flooding in London and in rural areas to the north will be repeated, says Steve Jackson, water resources engineer for the Maitland Valley Conservation Authority.

Jackson says that rainfall patterns are changing. In some areas, the rainstorm that struck in western Ontario after Christmas last year was a 100-year storm. But that doesn't mean that such a storm will happen only once every century, notes Jackson; it really means it has a "one per cent chance" of occurring. And drains and ditches designed to contain "100-year storms" are aimed at summer rainfall and don't take snow melts into account. "We had more lake-effect snow than we've had looking over 30 years of data," he says.

Water temperatures are also higher, making for more winter storm events, and rains are coming in a much shorter period than before. A rainfall that typically fell in eight to 10 hours now falls in three to four hours.

This will become more important for the design of municipal drains, Jackson says. Many are typically designed to hold a six-hour rainfall. Now, the same volume of rain comes down in a couple of hours. That changes the peak flows in ditches considerably.

He says the trend towards more violent storms is likely to continue. BF