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Chapter 2: Climate and Weather Impacts on Flood Risk

Are Floods Becoming More Common and Dangerous?

After the Delaware River experienced three damaging floods in less than a two-year period (September 2004, April 2005 and June 2006 – see this description of recent flood events in the basin), some residents began asking if floods were getting worse, and whether something was causing them to get worse. This chapter covers the regional climate and weather that can affect flood risk.

To make an important distinction up front, weather is a subset of climate. For example, it has been said that weather is what sweater you might wear on a cool day, but climate is how many sweaters you have in your closet. Climate studies cover the bigger trends and help us understand what current scientific data shows us about the risk of floods in the Delaware Watershed region.

More information about regional and local flood frequency can be found in Chapter 3 of this Understanding Flood Risk series.

In the video that follows below, we will meet the Pennsylvania State Climatologist, to see what observable trends imply about local/regional flood risk. But first, a brief glimpse into the subject:

The public understanding of global climate change includes a lack of clarity on three primary questions:

1. Is global climate change really happening?
2. Is mankind a major factor?
3. Is the burning of carbon-based fossil fuels the major culprit?

The answers to these questions are being studied heavily by academic researchers, scientists, government agencies and others, and predictions about the impacts of flooding suggest that in the Northeastern region of the United States, more extreme weather events – including floods and droughts – may be more common.

But even without a full understanding of the factors affecting climate change, we do know this: Climate changes. Whether it’s as dramatic as an ice age or as subtle as a wet or dry year you might experience locally, climate does change and we have, even in our small amount of time collecting records, solid evidence that it does. In this piece, we will focus not on predictions for future, but on the generally observable trends that we have data to support about changes at the local/regional level and what that means for flood risk.

The most important questions are:

Is the amount of annual precipitation in our region changing?

And the all important question for flood risk: Is the annual rainfall coming in smaller amounts over time (what we might consider normal), or, for example, are things trending toward the region getting a lot of rain in larger, but less frequent, storm events with dryer spells in between?

See below for an interview with Paul Knight, Pennsylvania State Climatologist with Penn State Meteorology and Atmospheric Sciences.

Click here for the data sheet that shows how PA is getting more rain now than previously in recorded history.

Click here for a report about monitoring trends in weather extremes.

Answer: The data indicates that Pennsylvania is getting more annual precipitation, so we might expect floods may occur more frequently in a general sense. It is simply too early to say if climate change is causing more floods right now. But the more extreme weather patterns we are seeing are consistent with climate change models. And more extreme weather is expected to lead to more floods with longer drought cycles in between. There is more input on this in the next chapter.

Note: There are some limits to just focusing on local patterns because we know that warmer ocean temperatures in the Tropics can produce more hurricanes. And more hurricanes increase the likelihood that one might make it all the way up the Eastern Seaboard and turn inland – the recipe for some of the big flood events we’ve seen on the Delaware.

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