Flash flooding in Maryland: freak event? climate change symptom? urban runoff problem? Or all of the above?

On Saturday night, as many people were enjoying an evening out in Maryland, and I was enjoying an evening in in Ohio, a tweet from Johns Hopkins professor and Baltimore resident, Dr. Sarah Horst caught my eye:

She followed up with a video and an offer for people to come whitewater rafting on her driveway. After those tweets, I found a virtual deluge (pardon the pun) of tweets from Baltimore and surrounding residents describing unbelievable rainfall and swiftly rising waters. Soon, reports of people trapped in cars and swiftwater rescues underway began to pour in, from parts of the Jones Falls stream valley in Baltimore and from Ellicott City, 10 miles to Baltimore’s West.

Red metal bridge with words Ellicott City on it, street under bridge has cyclists, stone buildings in background.

Downtown Ellicott City, in drier times. Photo by Scott Sagihirian used under a Creative Commons license. Sourced from Wikimedia.

Ellicott City is well-known in the Baltimore-Washington area for its historic downtown with a wide selection of shops and restaurants, which would likely have been quite popular on Saturday evening. I remember a fun evening out there a few years after college, when I had a mini-reunion with my roommates.

But this Saturday evening it started to rain. And then it began to rain really really hard. And then the floodwaters began to rise:

By the light of day, the extent of the damage became clear.

Cars washed away and stacked on top of each other (imbricated in the flow direction). First floors of stores and restaurants covered in mud, with 200 buildings damaged, some probably beyond repair. Sidewalks buckled, ripped away, and collapsed. Harrowing tails of escapes upstairs, up ladders, and uphill. Rescued people via human chains and via emergency responders. Two dead. Washed away in the torrents.

Ellicott City had received 4.5 inches of rain between 7:30 and 8:30 pm and more than 6.5 inches of rain over the course of the evening. Some estimates of the rainfall amounts are even higher, but all show Ellicott City as the bullseye of the downpour:

This amount of rain in such a short time blows our precipitation records out of the water. (Sorry, the puns just write themselves.) No official records are kept in Ellicott City, but based on nearby records, the rain event has a probability of something like 0.1% in any given year. We often call this a 1000-year storm, but just because it happened in 2016 tells us nothing about whether it will happen again in 2017, so probability is a better way of expressing that. Of course, precipitation records are nowhere near long enough to tell us about 0.1% probabilities, so what can really be said is that this rain event was unprecedented in the 100-200 or so years of records we have for the site.

Being caught in a record-breaking deluge is enough to put a damper on a Saturday evening out, but being caught in that sort of rain storm on Main Street of Ellicott City is a disaster. Ellicott City has the hydrologic misfortune of being located where three streams come together in a narrow valley. The combined stream runs right along the back of Main Street businesses, before funneling into the Patapsco River.

Topography draining to Ellicott City's Main Street, via Google Maps.

Topography draining to Ellicott City’s Main Street, via Google Maps.

I’ll have another post, later, that puts Saturday night’s flooding into the historical context of flooding in Ellicott City and the surrounding area. For now, let’s just say that this is hardly the first time Main Street has seen raging waters pass through the business district. What made Ellicott City a good location for water-based transportation and milling in the 1700s makes a risky location for a town ever since.

As resdients and business owners begin to clean up from yet another flood, they might be asking themselves a few questions: “Does it make sense to rebuild in a place with such a history of flooding?” That’s a question whose answer depends on economic decisions about acceptable losses in the insurance world and personal and societal decisions about acceptable risks.

Residents, business owners, and insurers might also be asking themselves a science question: “Does our changing climate make events like this more likely?” The short answer is, yes, although attributing the increased chances of any single event to climate change is a complicated business. But there is good evidence that extreme precipitation has increased in intensity over the past few decades, and our climate models suggest that intense rain events will continue to get more intense in the future. That’s because a warmer atmosphere can hold more water vapor, making available more water in the sky when it all comes pouring down on a place like Ellicott City. While the details of exactly where and how much precipitation extremes will increase are still an area of debate, some writers are beginning to describe climate change as weaponizing our atmosphere. Maybe that’s a bit hyperbolic, but people trapped in the floodwaters Saturday night might not think so.

There’s one more thing that likely contribute to Saturday night’s disaster and makes matters worse for Ellicott City now and in the future.

Satellite view of the landscape upstream of Main Street Ellicott City, via Google Maps.

Satellite view of the landscape upstream of Main Street Ellicott City, via Google Maps.

Water flowing into a curbside stormdrain

Storm drain receiving urban runoff. Photo by Robert Lawton, used under a Creative Commons license from Wikimedia.

Zooming out on the map shows that the streams flowing downhill to Ellicott City are draining increasingly urbanized areas, where precipitation has no chance of infiltrating if it falls on pavement or rooftops. Instead, rain on these impervious surfaces will be quickly routed to the stream via pipes or drains. Hopefully it makes a stop in some sort of stormwater management structure along the way, but those structures aren’t typically designed for anywhere near this intensity of rainfall. Older developments usually lack stormwater management features entirely. How effectively stormwater management structures can reduce the effects of urbanization on runoff is my area of active research, and to sum the literature up succinctly, what I can say is this: There is not a lot of strong evidence that stormwater management as it has been practiced is very good at reducing peak streamflow at the watershed scale. Instead what we see is that as urbanization intensity increases, so does the size of the flood peak. Bad news for Ellicott City.

So was Saturday night’s flash flood a freak event with a 1-in-a-1000 probability? Was it a symptom of an increasingly extreme climate system? Or was it manufactured by urban land use and inadequate stormwater management upstream? It’s quite possible that it was all three. Further, given the geography of Ellicott City and all of the above factors, a flood like this was an eventual inevitability. It’s just too bad for those who set out to enjoy a night out that it happened to be this particular Saturday night.

Categories: by Anne, climate science, geohazards, hydrology

A week in the life of a scientist – Anne’s first week of summer

Spring semester 2016 is over! Grades were submitted Saturday night, and my research group was eager to get started with our summer research. Since I’m semi-participating in the #365scienceselfies project, I have some fun documentation of our adventures this week.

Categories: by Anne, fieldwork, in the lab, photos

Environmental Earth Science in the News – Spring semester 2016 compilation

Students in GEOL 21062, Spring 2016, at Kent State University have been sharing interesting news stories with me all semester long. Here’s our complilation. Hopefully these are interesting things for other people too!

Categories: climate science, environment, links, society, teaching

Snapshots of the Middle Cuyahoga River on World Water Day

Categories: by Anne, fieldwork, hydrology, photos

A year of Anne’s reading – looking back

A post by Anne Jefferson For the last year, I’ve tweeted every paper I read. Inspired by Jacquelyn Gill’s resolution and hashtag #365papers, I wanted to spur myself to read more and to see how well I did. I never thought I’d read 365 papers, but I really didn’t have a sense of exactly how much I was reading, other than “far fewer than I download and put in my ‘to read’ folder.” Now, as the year draws to a close, I know how many papers I have read (78) and quite a bit more about my reading patterns. Plus, I know lots more cool science than I did this time last year.

In addition to tweeting all of my papers, I compiled a storify in order to keep track of my reading. In addition to letting me check what number paper I was on, I also found myself using the storify as a way to quickly recall the title of a paper I’d read. And today, I decided to data mine the tweets and quantify my 2015 reading.

What types of things did I read?
56 journal articles
4 journal articles that I co-authored that appeared in press in 2015
14 grant proposals as a reviewer
3 manuscripts as a reviewer
1 government technical report “cover to cover”
uncounted student thesis drafts and homework assignments
a gazillion really informative blog posts and on-line articles from which I learned a lot of science

I read and reviewed a lot more proposals this year than ever before. I also reviewed a lot fewer manuscripts than I had the past several years (in part because of all the proposals, but also because I declined reviews while on maternity leave). While I absolutely learn a ton of science reviewing proposals, I want to make sure that I don’t forsake reading papers that are directly useful (and citable) in my own work because I’m spending so much time on proposals. Something to watch for next year!

How did I get access to things I read?

  • Of the 61 journal articles, 15 (24%) were available open access on the publisher’s website, either because the whole journal is open access (e.g., Plos One, HESS), older articles are now available open access (e.g., AGU journals older than 2 years), or the authors paid for open access.
  • Many more articles are available via ResearchGate, author websites, university archives, or various uploads, so the actual proportion of articles I had to use my university access to get was lower.
  • Even with good university access, there were articles I wanted to read that I had a hard time getting. And there are articles I haven’t been able to read that I really wish I could.
  • A lot of my reading was done on my tablet while holding a baby, and I found that I gravitated towards articles that were OA because I didn’t want to deal with the hassle of figuring out how to get the VPN working and download a PDF. In a somewhat surprising development, I found that I really appreciated that journals that had nice HTML versions of they articles available OA because they were more screen friendly than the PDFs I usually read.

Who wrote the things I read?

  • Inspired by a discussion with Jacquelyn Gill and Meghan Duffy, I quickly counted the proportion of woman first authors among the journal articles I read, and I was pleasantly surprised. Of the 61 articles, 20 had woman first authors (33%).
    33% is actually better than the 20% of US earth science faculty positions filled by women, though lower than the 40+% of geoscience PhDs awarded to women.
  • However, the number of unique woman first authors is somewhat lower (as is the number of man first authors).
  • And, my own papers turn out to bias the statistics. Of the four papers, I’m an author on this year, three have woman first authors (all different!). Removing my papers from the list, we find 30% of the papers I read had woman first authors.

When were the papers written?

Graph of number of papers versus year with huge peak in 2015.

My 2015 article consumption has a decidedly non-normal distribution, and this is probably perfectly “normal” for someone who has been reading the literature for several years.

I love this result, because it’s pretty much what I think “keeping up with the literature” should look like for someone who has been working in the same field for at least a few years. I’m reading a lot of new papers that come across my radar by email alerts. I’m finding plenty of papers out in the past few years that slipped past my detectors at first but are showing up in the citations of new papers. And I’m revisiting some old favorites and classics that have stood the test of time. My paper age distribution would have looked much different in graduate school or when I first started working in urban hydrology, as I frantically tried to “catch up” with the state of the science.

median publication date for things I read this year: 2014
weighted average publication date: 2010

What were the top journals I read this year?
Journal of Hydrology (7)
Water Resources Research (5)
Environmental Science and Technology (3)
Geophysical Research Letters (3) (even though we don’t have an institutional subscription and I can’t get new papers)
Hydrological Processes (3)
Journal of Environmental Engineering (3) (even though I have difficulty accessing new papers from ASCE journals)
Plos One (3) (yay open access)

In total, I read from 38 journals. I’m impressed by that.

When did I read and review?

Line graph showing peak reading in January and lowest reading in June.

Interesting. Very interesting.

I read the most papers in January. I also gave birth in early January. Newborns don’t do very much, but they like to be held. In this case, correlation is evidence of causation. Note that my reading rate declines as the baby becomes more active. It’s lowest in June, as it should be, since we were on vacation for several weeks. I’m mostly troubled by the October slump, for which I have no excuses other than mid-semester busy-ness. Even with classes and grants and conferences and grading, I’d like to feed my brain a bit better throughout the semester.

Any favorite papers?
There are so many good papers out there, but if I had to pick just one to rave about it, it would definitely be:

Lundquist, J. D., N. E. Wayand, A. Massmann, M. P. Clark, F. Lott, and N. C. Cristea (2015), Diagnosis of insidious data disasters, Water Resour. Res., 51, 3815–3827, doi:10.1002/2014WR016585.

It’s even open access, and so, so good for anyone who takes in and makes use of field data.

Categories: academic life, by Anne