Climate change is often talked about in terms of heat, but one of its most immediate impacts is water in the atmosphere.
As the atmosphere warms, it can hold more moisture. In fact, for every degree Celsius increase in temperature, the air can hold about 7% more water vapor. That extra moisture has to go somewhere. When conditions are right, it falls as rain, often quickly, intensely, and in concentrated bursts. Add to that warmer oceans (which fuel storms) and shifting weather patterns that can cause storms to stall over one area, and you get a new reality: heavier, more unpredictable rainfall.
The challenge is that our cities were not built for this version of the climate.
Most urban drainage systems (storm sewers, culverts, retention basins, etc.) were sized using historical rainfall data. Engineers planned for what used to be considered “extreme” events, like a once-in-100-year storm.