![]() ![]() Having read the articles, some questions came to mind.ĭid Dr Yaacob have the statistics at hand, when he described the first, 16 June storm as being "once in 50 years", when the statistics clearly show that it wouldn't even have made the top 10 over the past 5 years? And yet, the recent areas flooded, such as Orchard Road, Opera Estate and Jalan Boon Lay, are not on that list. Presumably, these make up the 66 hectares of flood-prone areas today (yes yes, down from 3,178 hectares in the 1970s, as PUB, Dr Yaacob and others have reminded us). PUB lists 52 low-lying, flood-prone zones.On the other hand, the more recent storm on 17 July brought down 114mm at Lower Pierce Reservoir, but 194mm at Poole Road in Tanjong Katong.Averaged over 2 hours, that was about half the rainfall of the top 10 recorded rainfalls from 2006 to 2009. By comparison, the 16 June storm that flooded Orchard Road saw 101.6mm in 2 hours.The last 10 such occasions highlighted in the article (which seemed to exclude the recent floods) ranged from 101mm to 137mm.The highest one-hour rainfall ever recorded was 148mm in November 1995.If that is the case, then based on the USGS explanation of a 50-year flood, we probably need to re-define what a 50-year flood means in our context. In other words, we've been getting the so-called 50-year flood two or three times a year. Out of those 10 occasions, 8 resulted in floods.Flooding can be expected when more than 100mm of rain falls in an hour. ![]() ![]() Here are my key takeaways from the piece: So that made for a really good segue to a full-page article on page A8 of today's ST (July 22, 2010), headlined " 100mm: Expect floods if this much rain falls in an hour". A reader recently pointed out that a "50-year flood" is not literally a once-in-50-years flood. ![]()
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