Skip to main content

The Rainfall Every Hundred Years

RainfallEarlier this year, the Fort Calhoun nuclear facility in Nebraska was surrounded by the Missouri River, which jumped its banks due to a strong winter runoff and heavy spring rains. That flood was characterized as a 100-year event. 

Is a 100-year event like the cicadas that swarm the Washington area every 17 years? No, not at all. The cicadas arrive on a predictable schedule. Seventeen years elapse and there they are again.

This is a better description of a 100-year event:

Of course, return period doesn’t mean that we won’t see that kind of rain in those locations for several decades (or centuries). A 1 in 100 year rain means that there is a 1% chance of seeing that amount of rain in any given year. A 0.1% chance is true for a 1 in 1000 year event.

I assume that the 1 in 100 number changes every time something similar takes place – obviously, the odds of it happening in a given year drop if it happens more frequently. In any event, what is being discussed here is the rainfall in the Washington area last week.

On Thursday, September 8, Ft. Belvoir [in Virginia] received an astounding 7.03” of rain in three hours. According to the National Weather Service (NWS), that amount of rain in that amount of time was an “off the charts above a 1000-year rainfall (based on precip frequency from Quantico).”

The rain every thousand years – good title for a novel. There’s more (a bit edited – see the link for more):

  • The Bowie IFLOWS gauge recorded 4.57 inches in 3 hours, which is about a 200-year rainfall.
  • For Upper Marlboro and near Ellicott City, Wednesday’s rains were a roughly one in 50-100 year event.
  • For Westview , Wednesday’s rains were a roughly one in 10-25 year event.
  • The Kingstowne IFLOWS gauge in Fairfax County recorded 5.47 inches in 3 hours, which is approximately a 500-year rainfall for that timeframe.
  • The Reston IFLOWS gauge in Fairfax County recorded 6.57 inches in 6 hours, which is also approximately a 500-year rainfall.

These places are all in Virginia and Maryland.

One might be tempted to ask: Global warming?

Although the ties between climate change and extreme weather events often elicit absolute statements from advocates on various sides of the climate change issue, the reality is that while much can be said, much remains unknown. The challenge for reporters as well as scientists is to accurately convey both the scientific findings and the uncertainties surrounding them.

So perhaps, perhaps not. But:

The physical mechanism behind the link between warming global average land and ocean temperatures and more frequent heavy precipitation events is rather simple to understand - as air warms, it can hold more water vapor, which means that more water can then be squeezed out of the atmosphere as liquid or frozen precipitation.

So, um,maybe more perhaps – in intensity if not frequency – so it may be that a strong rainfall previously thought a 100 year event becomes a 50 year event because the intensity of rainfall generally increases. Or the floods along the Missouri become at least somewhat more frequent. (Tornadoes need not apply – different dynamics.)

A report published by the Bush administration in 2008 (based in part on the work of the U.N. IPCC, but focusing specifically on North America) had already concluded that human activities are associated with changing characteristics of certain kinds of extreme weather events, and the evidence keeps on accumulating.

And keeps on accumulating. The world has not stopped working on this issue, and the United States – industry and government and plain old folks – are still working on mitigating the effects of climate change. While there are countervailing forces, certainly, there is also a strong forward momentum.

Nuclear energy has different parts to play in different issues, but it plays its part in this one just by existing and expanding its share of U.S. electricity generation – if not quite yet, soon. So do solar, wind, hydro and other energy sources.

In the meantime, the river will rise and the rain will fall.

Comments

It doesn't affect the article, but it is worth noting what the weather bureau means when they talk about a 1000 year rainfall, or for that matter when they say that there is a 50% chance of rain tomorrow.

Weather forecasts, including those of extremes, cover areas, not a single geographic point. So on average there will be one thousand year rainfall event per year, per every thousand locations covered. Similarly if the weather forecast for your area is a 50% chance of rain tomorrow, the expectation is that half the area buildings will get rained on. (Those people who move around a lot will tend to get rained on part of the time.)

Are there more than one thousand areas in the US that will have significantly different weather over the course of a year? Probably, although a lot of them will be in Alaska. So a couple of extreme (local) weather events per year are not surprising.

Popular posts from this blog

Sneak Peek

There's an invisible force powering and propelling our way of life.
It's all around us. You can't feel it. Smell it. Or taste it.
But it's there all the same. And if you look close enough, you can see all the amazing and wondrous things it does.
It not only powers our cities and towns.
And all the high-tech things we love.
It gives us the power to invent.
To explore.
To discover.
To create advanced technologies.
This invisible force creates jobs out of thin air.
It adds billions to our economy.
It's on even when we're not.
And stays on no matter what Mother Nature throws at it.
This invisible force takes us to the outer reaches of outer space.
And to the very depths of our oceans.
It brings us together. And it makes us better.
And most importantly, it has the power to do all this in our lifetime while barely leaving a trace.
Some people might say it's kind of unbelievable.
They wonder, what is this new power that does all these extraordinary things?

A Design Team Pictures the Future of Nuclear Energy

For more than 100 years, the shape and location of human settlements has been defined in large part by energy and water. Cities grew up near natural resources like hydropower, and near water for agricultural, industrial and household use.

So what would the world look like with a new generation of small nuclear reactors that could provide abundant, clean energy for electricity, water pumping and desalination and industrial processes?

Hard to say with precision, but Third Way, the non-partisan think tank, asked the design team at the Washington, D.C. office of Gensler & Associates, an architecture and interior design firm that specializes in sustainable projects like a complex that houses the NFL’s Dallas Cowboys. The talented designers saw a blooming desert and a cozy arctic village, an old urban mill re-purposed as an energy producer, a data center that integrates solar panels on its sprawling flat roofs, a naval base and a humming transit hub.

In the converted mill, high temperat…

Seeing the Light on Nuclear Energy

If you think that there is plenty of electricity, that the air is clean enough and that nuclear power is a just one among many options for meeting human needs, then you are probably over-focused on the United States or Western Europe. Even then, you’d be wrong.

That’s the idea at the heart of a new book, “Seeing the Light: The Case for Nuclear Power in the 21st Century,” by Scott L. Montgomery, a geoscientist and energy expert, and Thomas Graham Jr., a retired ambassador and arms control expert.


Billions of people live in energy poverty, they write, and even those who don’t, those who live in places where there is always an electric outlet or a light switch handy, we need to unmake the last 200 years of energy history, and move to non-carbon sources. Energy is integral to our lives but the authors cite a World Health Organization estimate that more than 6.5 million people die each year from air pollution.  In addition, they say, the global climate is heading for ruinous instability. E…