Many events are measured in terms of probability of 5 year, 10 year, 100 year etc. My parents homestead went thru that tropical storm Irene 4 years ago and that was more than a 50 year event, but not a 100 year event as I recall.
Regarding the recent rains in North and South Carolina. is that really a 1,000 year event ?
It being a media report, things like “100-year storm” and so forth are probably exaggerated or based on some limited factor - e.g., it’s been 100 years since more than 2 inches of rain fell on that date.
But fact is we’re getting 100-1,000 year events with regularity, all over the continent, and records for heat and precipitation (both ways) are falling nearly every year. I think California is around the 1,200-year mark for the current drought.
Welcome to the new normal, the result of a planetary atmosphere that’s been pissed in too long.
Not just a media event reporting but science based facts and statistics on probability.
Explained decently in an L. A. Times story
I wasn’t questioning that there was some fact or stat underlying the claim (and most such claims). The reach for superlatives and hyperbole seem to drive such categorizations, though, and I suspect that in many cases the long span of time includes more than a few near-misses… e.g. 1.9 inches of rain on that date a few times during the interval.
But no question we’re in a wild time, and it’s going to get wilder. The media may as well flog this XXXX-year stuff while they can. 
Strictly speaking, a “1,000 year event” is defined as an event that has a probability of occurring in any given year as 0.1%. This means that, on average, out of every 1,000 weather stations, one will have a thousand year event every year. This could be as mundane as a very high overnight low temperature or it could be catastrophic rainfall.
We only have weather records for the past … say … 150 years. Any event in the 1,000 year or 10,000 year probabilities will seem to be an ‘extreme’ event, but alas it would be perfectly normal and expected. The recent rainfall in South Carolina is usual and normal, it just doesn’t happen all that often.
Citation: 100-Year Flood–It’s All About Chance
I wonder if there is an upper limit on this scale: Are there “5,000 years events”, “10,000 years events” or maybe “100,000 years events”?
Estimating what a 1000-year event would be is non-trivial, if you have much less than 1000 years of data. A novel “power-law” approach developed by Harry Hurst to plan water containment on the Nile River was made famous by Benoit Mandelbrot.
You can get as silly as you want. Just now I Googled Harry Hurst while eating popcorn. That’s probably a 1000-year event.
Of course, weather events are judged based on the past. A flood as bad as the recent one might be expected several times in Charleston during the next 1000 years if you [del]swallow the doom-saying of Al Gore[/del] accept climate science.
The limit is how difficult it is to assign probabilities to extremely rare events given our limited knowledge of how this stuff works.
Yeah, there is such a thing as a “10,000 year event”; it’s just that we don’t really know what it is.
Well FEMA goes by 100 year flood events to determine if you are in a flood plain so there are some “real” effects of living in such an area such as increased mandatory insurance on property mortgages and a decrease in property value. A 1000 year event may be something like a earthquake or volcanic eruption and there may very well be some basis for making such an assumption. And then there are mass extinction asteroid hits, of which we are due any time now.
Our newspapers keep telling us that the weather is getting worse. They back this up by saying that yesterdays rain/flood/snow/wind was the worst since 19xx. This seems to me that back in 19xx it was at least as bad as now…
Moderator Note
Let’s avoid political jabs in General Questions, even intended as a joke. No warning issued.
Colibri
General Questions Moderator
Weather is chaotic and subject to dozens of cycles from hourly to millennial or longer. The fact that there was a storm, or tide, or flood of the same magnitude once before does not mean that another one is normal. It is that the incidence of such record-breaking occurrences is increasing, and growing more widespread. Look at the last couple of years: it was not a case of a 100-year flood here, a 50-year storm there… it was such things on an almost continuous basis all across the US.
Two 100-year events in a single year?
That’s not how that works at all. It’s independent of the number of monitoring stations.
For any given area, rain falls in a particular distribution over time. “X-year flood events” are merely the way that the meteorologists describe the probability of a given amount of rainfall is to happen.
So for example, a 3 year flood event (what most residential streets in Texas are engineered to handle) happens, on average, every 3 years. It may happen more or less often than that. Same thing for a 25 year flood event- on average, one happens every 25 years or so. And it’s the same on up- a 1000 year flood event happens on average every 1000 years, so it’s pretty rare.
Past about 100 years, it’s probably a combination of statistics and geological record; I’d imagine that a 1000 year flood event could be seen in the fossil record, as could a 10,000 and a 100,000 year record.
At the family homestead which recently suffered a 90, or so, year flood event the local town wants to implement ordinances that require new construction in that part of town to be able to withstand a 500 year flood event. Not sure if it will pass, but that is the proposal.
Given we don’t have temperature records for much over 100 years and that’s spotty at best around the world I’m inclined to ask you for a cite.
Make it “what are considered 100-year or more events,” if you like. I don’t have nor claim to have the ability to judge the veracity of such claims, but many are made by more reliable entities than local media.
Do you disagree that the US is seeing far more anomalous weather events in recent years, of greater frequency, severity and duration?
It’s always difficult to know whether there is a real increase or just and increase in reported events. Communications have improved dramatically in the last couple of decades and even trivial events get reported now.