Katelyn Weisbrod | May 31, 2018

A Maryland city endured a devastating 1,000-year rainstorm this week, leading to a second flash flood of this severity to hit the town in less than two years.

On July 30, 2016, nearly six inches of rain fell in about an hour and a half in Ellicott City, Maryland, leading to a flood that devastated buildings and killed two people. On May 27, an arguably worse flood ravaged the same area.

An analysis done by The Washington Post attributed the 2018 flood to the area’s funnel-like geography, nearly 10 inches of rain, meteorological forces, and possibly climate change.

However, the analysis pointed out, climate change cannot be a simple explanation for the event that was all too familiar for the people of Ellicott City. This was a single event in a relatively small area, and climate entails long-term trends in often large areas. But increased rainfall is a side effect of climate change, and that may have exacerbated this event.

A 1,000-year rainstorm does not necessarily mean that it only happens once every 1,000 years, but rather the likelihood of it happening in a given year is one in 1,000. For this to happen in Ellicott City twice in two years is incredibly unlikely, but possible.

With climate change and limited historical data, however, it is difficult for experts to accurately determine how frequent these events may be in the future. Iowa has also had its share of devastating floods in recent years — the floods of 1993 and 2008. In some locations, the 1993 flood was considered a 100-year flood, and the 2008 flood was in some places an even more severe 500-year flood, yet they happened within just 15 years of one another.