Streamflow Changes


Annual mean streamflow has increased over the last seven decades in the Susquehanna, Potomac, and James Rivers.

It is obvious that streamflow is a very important to the Chesapeake Bay. In fact, the input of fresh water from major rivers, such as the Susquehanna, is what makes Chesapeake Bay an estuary!

Streamflow changes can affect the Chesapeake from swings in salinity to altered deliveries of water soluble nutrients like nitrate. So of course we wanted to look at the historical changes to streamflow (today!) and how that is connected to our precipitation-based climate indices (next week!).

One of the purposes of this blog is to show you the reader what the researchers on this project are doing in real time. The data and images you are about to see are “freshly made” just a few minutes from this post’s scheduling!


The Potomac and James Rivers have increased in the spring season but the Susquehanna has decreased!

In this week’s post, we will looks at the historical changes to streamflow in the Susquehanna, Potomac, and James Rivers.

The Susquehanna

The Susquehanna is the greatest freshwater contributor to Chesapeake Bay with its watershed including large parts of Pennsylvania and New York.

So have there been any significant changes in streamflow? The answer is yes!

Winter, summer, and fall all have observed discharge increases since 1937, with the greatest increase being in the fall. Interestingly, there was a decrease in the spring flow. This is very important since the spring pulse of freshwater from melting snow can be an important factor in Bay-wide productivity.


Summer discharge; that huge spike is from hurricane Agnes in 1972!

Another interesting note: look at that huge spike in the summer mean discharge! That’s from Hurricane Agnes!

The Potomac and James Rivers

The Potomac and James Rivers saw streamflow increases across the board! All seasons have observed discharge increases, with the exception of summer in the James River which had an insignificant trend. While the summer trend in the Potomac was significant, it was the smallest decadal rate of change observed in these three time series.

Again, the fall observed the greatest increases…which is likely related to increases in autumnal precipitation (more on this next week!)


Final Thoughts

 The arguably three greatest inputs of freshwater into Chesapeake Bay have all observed changes in the past few decades. You will see next week how this observation is related to our climate extreme indices!

Kari Pohl

About Kari Pohl

I am a post-doctoral researcher at NOAA and the University of Maryland (Center for Environmental Science at Horn Point Laboratory). My work investigates how climate variability and extremes affect the diverse ecosystems in Chesapeake Bay. I received a Ph.D. in oceanography from the University of Rhode Island (2014) and received a B.S. in Environmental Science and a B.A. in Chemistry from Roger Williams University (2009). When I am not busy being a scientist, my hobbies include running, watching (and often yelling at) the Boston Bruins, and taking photos of my cat.
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