它是确定几百年洪水有限方差吗?- 江南体育网页版- - - - -地球科学堆江南电子竞技平台栈交换 最近30从www.hoelymoley.com 2023 - 04 - 12 - t17:16:03z //www.hoelymoley.com/feeds/question/15815 https://creativecommons.org/licenses/by-sa/4.0/rdf //www.hoelymoley.com/q/15815 3 它是确定几百年洪水有限方差吗? J•托马斯 //www.hoelymoley.com/users/12787 2018 - 12 - 22 - t17:53:25z 2018 - 12 - 24 - t02:23:59z < p >我就想到问这个。< / p >

It's easy to get a statistical distribution that does not have finite variance. For example, you can sometimes get that when the thing that is measured comes from two random variables, one divided by the other. Sometimes you can't measure a variance. Sometimes you can get a statistical distribution that doesn't even have a mean.

When that happens, if you don't notice, you can get a mean and standard distribution from the data. And when you collect more data it will seem to mostly fit. But you get big outliers more often than you'd expect. As you recompute your mean and standard deviation, with more data the standard deviation keeps increasing. Because the longer you keep measuring, the more unexpected events you will have that go outside the predicted range.

Without knowing much at all about floods, they seem to fit this pattern. The news keeps announcing floods that were supposed to be unlikely, unexpected.

Of course, for all I know this is just the news reporting things that should have been expected. Of all the thousands of places we calculate hundred-year-flood levels for, every year we should expect floods that high at one percent of them. Maybe what's happening is really exactly what should be expected.

But it's testable. With enough data you can check whether flooding ought to fit a finite-variance distribution or not.

How well has it been tested?

//www.hoelymoley.com/questions/15815/-/15821 # 15821 4 rivercfd的回答是肯定,几百年洪水有限方差吗? rivercfd //www.hoelymoley.com/users/14598 2018 - 12 - 24 - t02:23:59z 2018 - 12 - 24 - t02:23:59z < p >我相信统计大师在< a href = " https://stats.stackexchange.com/ " >旨在< / >可以回答这个你最好,但这里有一些一般信息估计洪水频率仅供参考。< / p > < p > < a href = " https://water.usgs.gov/edu/100yearflood-basic.html " rel = " nofollow noreferrer " > < / > 100年洪水的概率有1%发生在任何一年。它通常由拟合估计一些类型的一个极端值分布与额外的倾斜调整观察洪水峰值占上游地区影响或监管。在美国,标准的方法是适合一个< a href = " https://en.wikipedia.org/wiki/Pearson_distribution # The_Pearson_type_III_distribution”rel = " nofollow noreferrer " >日志皮尔逊类型III < / >分布对数转换观察洪水峰值。直到最近,< a href = " https://water.usgs.gov/osw/bulletin17b/dl_flow.pdf " rel = " nofollow noreferrer " >公告# 17 b < / >是联邦应急管理局批准方法洪水水文风险足够记录的洪水峰值时可用。取代了2018年3月,< a href = " https://acwi.gov/hydrology/Frequency/b17c/ " rel = " nofollow noreferrer " >公告# 17 c < / >,有一些改进的统计方法。< / p >

As far as your question regarding finite variance, my understanding is that the LP III distribution asymptotically approaches unity and thus remains unbounded without finite variance since from a risk perspective there could always be a larger flood that has not yet been measured. There are also methods for estimating a Probable Maximum Flood (PMF) that is meant to represent the most extreme combination of meteorological and hydrologic conditions that are reasonably possible in a catchment.

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